Bai Giang Hoa Phan Tich - Smith.N

8/7/2019 Bai Giang Hoa Phan Tich - Smith.N

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Hoa phan tch

CHNG 1. AI CNG VE HOA PHAN TCHI. NOI DUNG VA YEU CAU CUA HOA PHAN TCH

Hoa hoc phan tch, hieu theo ngha rong, khong nhng ch la khoa hoc

ve cac phng phap phan tch nh tnh va nh lng cac chat ma con la khoahoc ve cac phng phap kiem tra nhng qua trnh hoa ly va ky thuat hoa hoc.

Phan tch nh tnh (PTT) nham xac nh s hien dien cua cac cau t(ion, nguyen to hay nhom nguyen to) trong mau phan tch va ong thi anhgia s bo ham lng cua chung: a lng, vi lng, vet, PTT phan ln davao s chuyen chat phan tch thanh mot chat mi nao o co nhng tnh chatac trng nh co mau, co cau truc tinh the hoac vo nh hnh, co trang thai vatly nhat nh

Phan tch nh lng (PTL) co nhiem vu xac nh chnh xac ham lng

cua nhng cau t trong mau. Phng phap PTL da tren phep o cac thuoctnh hoa hoc, vat ly hoac hoa ly cua cac chat hoac cua cac phan ng hoa hoc.Cac phng phap PTL bao gom PPHH, PPVL, PPHL.

Vai tro chu yeu cua hoa phan tch la PTL. Tuy nhien trong thc temuon xac nh ham lng mot mau cha biet thanh phan rat phc tap, v s comat cua ion hay nguyen to nay thng can tr viec xac nh cau t khac. Doo, du co yeu cau hay khong, vi mot mau cha biet thanh phan phai tienhanh phan tch nh tnh trc e co the chon c phng phap PTL thchhp va cho ket qua chnh xac. Cac phng phap phan tch nh tnh va nh

lng cho phep xac nh ham lng cac nguyen to rieng re trong cac chat phantch c goi la phng phap phan tch nguyen to, e xac nh cac nhom chcc goi la phan tch nhom chc.

Da vao cac PPPT, ngi ta a tm ra nhng nh luat hoa hoc quantrong nh nh luat thanh phan khong oi, nh luat t le boi, nh luat tac dungng lng, xac nh cac nguyen t khoi cua mot so nguyen to, thanh lapc cong thc hoa hoc cua rat nhieu hp chat . Hoa hoc phan tch tao ieukien thuan li cho viec phat trien cac mon khoa hoc t nhien nh a hoa hoc,a chat hoc, khoang vat hoc, vat ly hoc, sinh vat hoc, y hoc, hoa ky thuat,cong nghiep luyen kim, va hoa hoc phan tch con la c s cho viec kiemnghiem hoa hoc trong nghien cu, san xuat (kiem tra nguyen lieu, ban thanhpham, thanh pham), xay dng cac phng phap kiem tra t ong cac qua trnhky thuat.

Vai tro cua hoa phan tch ngay cang cao cung co ngha la cac yeu cauoi vi nganh va ngi lam cong tac phan tch ngay cang khat khe hn. Vinganh phan tch, phai luon luon phat trien hau theo kp a phat trien cua cacnganh khac. Vi ngi phan tch, do co s tng quan gia cac nganh khoa hoc

t nhien nen ngi phan tch phai co kien thc ve cac mon toan, ly, hoa aicng, hoa vo c, hoa ly va tin hoc e co the nam vng nguyen tac cua cac

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phng phap va co the i sau vao cac phng phap mi da tren cac can bansan co. Ngoai ra, trong phan thc nghiem, ngi phan tch can co nhng aoc nh can than, kien nhan, chnh xac, sach se, trung thc va co kha nangphan oan ket qua phan tch.

II. PHAN LOAI CAC PHNG PHAP PHAN TCH (PPPT)Co nhieu cach phan loai cac phng phap phan tch, trong o pho bien

nhat la cach phan loai da vao ban chat (hay ac iem) cua phng phap hoacda vao ham lng cua cau t trong mau phan tch.II.1. Phan loai theo ban chat cua phng phap

Khi phan loai theo ban chat cua phng phap, hoa phan tch bao gomcac phng phap sau:Phng phap hoa hoc (PPHH)

Dung phan ng hoa hoc e chuyen cau t khao sat thanh hp chat mima vi tnh chat ac trng nao o cua hp chat mi, ta co the xac nh c shien dien va ham lng cua cau t khao sat.

V du: trong moi trng ammoniac, vi ham lng thch hp Ni2+ thamgia phan ng hoa hoc vi dimetyl glyoxim (DMG) cho xuat hien ket tua mauo son. Nh vay, khi cho dung dch DMG tac dung vi dung dch phan tch:

- Neu dung dch (DD) co xuat hien tua o son, ket luan co Ni2+ trongDD phan tch (nh tnh).- Tach va can tua ta xac nh c ham lng Ni2+ trong mau (nh

lng).Phng phap vat ly (PPVL)Phng phap vat ly la cac PPPT dung e phat hien hoac xac nh thanh

phan cua chat can nghien cu ma khong can phai s dung cac phan ng hoahoc. Cac phng phap nay co the la cac phng phap da tren viec nghien cucac tnh chat quang, ien, t, nhiet hoac cac tnh chat vat ly khac. PPVL co 1so u iem so vi cac PPHH nh co the tach c cac nguyen to kho b tachbi PPHH, de ap dung cho cac qua trnh t ong hoa.Phng phap hoa ly (PPHL)

Phng phap hoa ly la PPPT d tren s ket hp gia PPVL va PPHH:sau khi thc hien phan ng hoa hoc gia cau t khao sat va thuoc th, da vaoviec khao sat ly tnh cua hp chat thu c hay DD tao ra e nh tnh hoacnh lng mau.

Mac du xuat hien kha lau sau PPPT hoa hoc, cac phng phap hoa lylai c phat trien va hien ai hoa vi toc o rat nhanh, c s dung ngaycang rong rai trong cac phong th nghiem nghien cu khoa hoc va trong caphong th nghiem nha may, x nghiep. Nguyen tac chung cua phng phap ladung bien phap thch hp tac ong len oi tng nghien cu va ghi nhan s

thay oi cac tham so hoa ly cua oi tng nghien cu sau khi tac ong. equan sat va ghi nhan cac tham so hoa ly oi hoi phai s dung cac dung cu va

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thiet b kha tinh vi, phc tap. V ly do nay, cac PPPT vat ly va hoa ly thngc goi la PPPT dung cu hoac goi theo thoi quen la PPPT hoa ly. Cac PPPTdung cu thng c chia thanh cac nhom sau ay: (1) PPPT pho nghiem; (2)PPPT ien hoa; (3) PPPT sac ky va (4) la cac PPPT khac.

Cac phng phap pho nghiem (PPPN)Cac PPPN la cac PPPT ma ket qua khao sat co the bieu dien di dangpho. Thuoc nhom phng phap nay gom co cac phng phap quang pho(quang hoc) da tren s nghien cu cua cac pho phat xa, hap thu va tan xa anhsang. Phng phap nay con bao gom phng phap khoi pho (phng phapnghien cu cac chat bang cach o chnh xac khoi lng phan t cua chat o)va phng phap pho cong hng t da tren s tng tac cua nguyen t, phant chat khao sat vi t trng.

Ngoai cac phng phap tren, nhom cac phng phap phan tch pho con

bao gom PPPT da tren viec o chiet suat khuc xa cua vat chat; PPPT hamlng cac chat da tren s o lng anh sang va phng phap hap uc laphng phap da tren s o lng anh sang do mot huyen phu khong mau hapthu.Cac phng phap ien hoa (PPH)

Ngay nay a co ti khoang ba mi PPPT ien hoa khac nhau ma c scua phng phap da tren cac quy luat, hien tng co lien quan en phan ngien hoa xay ra tren ranh gii tiep xuc gia cac cc va DD phan tch, hoac davao tnh chat ien hoa cua DD tao nen moi trng gia cac ien cc, hoac da

tren cac ng dung cua phan ng ien hoa. Nhieu tac gia e ngh chia cacPPPT ien hoa thanh 2 nhom ln: (1) nhom cac phng phap da tren cac quatrnh ien cc va (2) nhom cac phng phap khong dung cac phan ng iencc.Cac phng phap thuoc nhom mot c chia thanh hai phan nhom:- Phan nhom gom cac phng phap trong o cac phan ng ien cc

trang thai can bang bao gom phng phap o the va chuan o ien thevi dong bang khong.

- Phan nhom da tren s ien phan (dong khac khong), bao gom phngphap volt amper, chuan o ien the vi dong khong oi, phng ienkhoi lng dong khong oi hoac the khong oi, phng phap cc pho coien, cc pho dong xoay chieu, phng phap ien hoa hoa tan.

Cac phng phap khong dung phan ng ien cc bao gom cac phng phapien dan va chuan o ien dan, phng phap xac nh hang so ien moi tngoi, phng phap ien dan cao tan va chuan o ien dan cao tanCac phng phap sac ky (PPSK)

Sac ky la qua trnh tach da tren s chuyen dch cua hon hp phan tchqua lp chat bat ong trang thai ran hoac trang thai long tam tren chat mangran (c goi la pha tnh) va s chuyen dch o c thc hien bang mot chat

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long hoac chat kh co kha nang di chuyen (goi la pha ong). Cac PPPT sac kycu the bao gom nhom sac ky hap phu (ran-kh, ran-long); nhom sac ky phanbo (long - long; long - kh), sac ky trao oi ion va sac ky ray phan t. Qua trnhtach sac ky co the xay ra tren cot hoac tren mat phang nh giay, ban mong.

Phng phap sac ky c s dung rong rai e tach nhng chat vo c vahu c giong nhau ve thanh phan va tnh chat, ac biet la co the tach c cacnguyen to at hiem va nhng nguyen to phong xa vi hieu qua kha cao. Ngoaikha nang tach, PPSK con c dung e nh tnh va nh lng rat nhieu loaimau thuoc lnh vc khoa hoc va lnh vc cong nghiep khac.Cac PPPT hoa ly khacNgoai cac nhom phng phap tren, thuoc nhom PPPT dung cu con co PPPTphong xa da tren s o bc xa cua cac nguyen to co hoat tnh phong xa, cacPPPT nhiet, PPPT nhiet ien, PP o o dan nhiet, PP chuan o nhiet lng va

mot so PPPT khac.u iem cua cac PPPT dung cu la o nhay cao, toc o phan tch nhanh,

lng mau phan tch be khi so sanh no vi PPPT hoa hoc:

Ch tieu so sanh Phng phap hoa hoc Phng phap dung cuLng mauTnh chon locThi giano chnh xac

Dung cuNgi phan tch

Ln (kem nhay)Khong caoChamChnh xac (*)

n gian, re tien

Nho (nhay)CaoNhanhChnh xac (*)

Toi tan, at tienTrnh o ky thuat cao

(*) Neu ham lng cau t trong mau khao sat khong qua be, o chnh xac cuabat ky PPPT nao cung khong the vt qua o chnh xac cua PPPT hoa hoc.Phng phap vi sinh

Dung e nh lng vet cau t da tren hieu ng cua chung vi toc ophat trien cua vi sinh vat.

Phng phap phan tch ong hocPhng phap nh tnh va nh lng cac nguyen to da vao viec s

dung cac phan ng xuc tac. V toc o cua cac phan ng hoa hoc phu thuoc vaonong o cua cac chat phan ng nen o toc o phan ng co the xac nh nongo cua chat phan ng. PPPT ong hoc co o nhay ac biet cao, gap nhieu lano nhay so vi cac PPPT khac (10-5 10-6 g/ml).Cac phng phap khac

Ngoai cac phng phap ke tren con mot so phng phap khac chu yeudung cho PPL.

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Phng phap nghienMau phan tch va thuoc th ran c nghien trong coi s, nguyen to can

tm c phat hien da vao s tao thanh cac hp chat ac trng co mau sachay co mui khac nhau. V du, nghien mau ban au vi KSCN, neu thay xuat

hien mau o mau tc mau cha cac hp chat cua Fe3+

.Phng phap nho giotPPPT da tren s mao dan va hap phu. Cac phan ng c thc hien

tren cac tam s, thuy tinh hoac giay loc. Khi s dung giay loc, chat long thamvao giay con hp chat mau c tao thanh b hap phu mot phan nho cuagiay loc lam tang o nhay cua phan ng. V du, e xac nh ion Mn2+, ngi tacham 1 giot DD phan tch len t giay loc va cho vet am bao hoa vi hiammoniac. Them 1 giot DD benzidine trong acid acetic. Mn(OH)2 tao thanhc oxy hoa thanh Mn(OH)3 va Mn(OH)4 nh oxy cua khong kh. pH = 5,

cac hp chat nay oxy hoa benzidine va tao thanh mau xanh cua xanhbenzidine.

Phng phap th nghiem ngon laMot so kim loai phat ra t bc xa co mau ac trng khi c ot tren

ngon la xanh cua en kh. V du:Na: la vang Ca: la o gachK: la o tm Ba: la o lucPhng phap soi tinh the di knh hien viDung knh hien vi co the phan biet c cac dang tinh the cua cac hp

chat sau nh:Phan biet SrCrO4 vi BaCrO4Phan biet CuSO4 vi BaSO4

nh tinh the cua chung co cau truc khac nhau ac trng.Phng phap ieu che ngoc borax hay phosphateMot so oxyt kim loai co the tao hp chat vi borax hay phosphate co

mau ac trng di ngon la tnh oxy hoa/kh hay trang thai nong/nguoi.V du:

Cu-Borax dang ngoc mau xanh am khi nguoiMn-Borax mau tm ngon la oxy hoaII.2. Phan loai theo lng mau phan tch hay ky thuat phan tchTuy ham lng cua cau t trong mau va PPPT, lng mau phan tch

cung khac nhau. Ta phan biet:Phan tch thoDung dung cu c 50-500ml va tach chat ran khoi chat long bang cach

loc. Lng mau s dung t 1-10g hay 1-10ml.Phan tch ban vi lngDung dung cu


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Phan tch sieu vi lngPhan tch di knh hien vi ien t va moi trng ac biet vi lng

mau s dung


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Phan ng acid-baz: Phan ng trao oi H+ gia oi acid/baz dung trong hoaphan tch e:1. Xac nh tnh acid hay baz cua DD bang cach o pH2. Hoa tan mau:

CaCO3 + 2 HCl CaCl2 + CO2 + H2O3. nh lng:HCl + NaOH NaCl + H2OPhan ng tao tua: Phan ng trao oi ion e tao thanh hp chat t tan, c s

dung e:1. nh tnh:

Ag+ + I- AgI vang2. Tach nhom:

Ag+, Pb2+, Hg22+ + HCl AgCl , PbCl 2 , Hg2Cl2

3. nh lng:SO4

2- + Ba2+ BaSO4 Phan ng tao phc: Phan ng ket hp ion e tao phc chat de tan, c sdung e:1. nh tnh:

Fe3+ + n SCN- [Fe(SCN)n](3-n)+ o mau

2. nh lng:Ca2+ + H2Y

2- CaY2- + 2 H+

3. Hoa tan:

AgCl + 2 NH4OH [Ag(NH3)2]+ + Cl- + 2 H2O4. Che cau t di dang phc ben:- Loai Ni2+: Ni2+ + 4 CN- [Ni(CN)4]

2-

- e tranh tao tua CuS v:[Cu(NH3)2]

2+ + H2S CuS5. Giai che (tra cac ion b che ve trang thai t do):

2 Ag+ + [Ni(CN)4]2- 2 [Ag(CN)2]

- + Ni2+

Ngoai cac acid va baz, DD cua nhieu muoi cung co tnh acid hoac kiem. Neudung moi la nc, gia nhng ion cua muoi vi nhng ion cua nc se xay raphan ng tng tac goi la thuy phan. Qua trnh thuy phan thng la qua trnhthuan nghch. V du:

Ba(CH3COO)2 + 2 H2O CH3COOH + Ba2+ + 2 OH-

NH4Cl + H2O NH4OH + H+ + Cl-

Al2S3 + 6 H2O 2 Al(OH)3 + 3 H2STheo ngha rong, s thuy phan la phan ng tng tac gia nhng chat

khac nhau (muoi, hydrua, hp chat cha oxy,...) vi nhng ion cua nc, kemtheo s pha huy can bang ien ly cua nc va lam thay oi pH cua DD. Trong

hoa phan tch, cac phan ng thuy phan c s dung e:

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1. Tao tua hidroxid: mot so thuoc th nh (NH4)2CO3, (NH4)2S, CH3COONa deb thuy phan tao thanh ion hidroxyl t do, tao cho DD co cac gia tr pH xacnh. Ngi ta s dung cac hidroxyl t do sinh ra e tao tua hidroxid nhieucation bang DD nc cua cac muoi thuy phan ke tren.

2. Tach cac chat ra khoi nhau da vao mc o thuy phan khac nhau cua cacchat khac nhau.3. Phat hien cac muoi anion b thuy phan tao thanh ammoniac t do.4. Phat hien cac ion ma muoi cua chung khi thuy phan tao thanh cac hp chatkhong tan. V du: BeCl2 khi thuy phan tao thanh BeO2Cl2 III.2. Yeu cau oi vi thuoc th dung trong hoa phan tcho tinh khieto tinh khiet la khai niem dung bieu dien ham lng hp chat X trong thuocth. Tuy vao ham lng nay, ngi ta phan biet:

1. Hoa chat ky thuat vi X 99.0%2. Hoa chat tinh khiet (P) vi 99.0% X 99.9%3. Hoa chat tinh khiet phan tch (PA) vi 99.90% X 99.99%4. Hoa chat tinh khiet hoa hoc vi 99.990% X 99.999%5. Hoa chat tinh khiet quang hoc hay ac biet vi

99.999% X 99.9999%Tnh chon locThuoc th phai co tnh chon loc (hay ac hieu) cao oi vi cau t khao sat X,ngha la thuoc th ch tac dung vi cau t X ma khong tac dung vi cac cau t

khac ong hien dien trong mau. V du, ho tinh bot la thuoc th co tnh chon locoi vi Iod.Tnh nhayThuoc th phai nhay, ngha la co kha nang phat hien cau t khao sat X khi Xhien dien trong mau vi ham lng thap. Tnh nhay cua thuoc th co the cbieu dien theo mot trong hai khai niem la gii han phat hien hoac o loanggii han.Gii han phat hien: la lng toi thieu cua X ( g/ml) ma thuoc th phat hienc. V du, gii han phat hien Cu2+ bang NH4OH la 4 g/ml, gii han phathien Fe3+ bang SCN- la 0.25 g/ml, Gii han phat hien con co the c bieudien bang nong o gii han hay nong o toi thieu.o loang gii han: la the tch dung moi toi a (ml) dung e hoa tan 1g cau tX ma co the phat hien c X.Ngoai cac ieu kien chung ke tren, thuoc th dung e pha DD co o ung cao(goi la DD chuan) con phai am bao them cac ieu kien sau:1. Tr oi vi moi trng2. dang vun, bot co the can c lng chnh xac en 1mg hay 0.1mg

3. Co phan t lng ln e giam sai so khi can.

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Cac hoa chat thoa man c ong thi cac ieu kien tren c goi la hoa chatchuan goc. Cac hoa chat chuan goc thong dung nh la: K2Cr2O7,(COOH)2.2H2O, AgNO3, Na2H2C10H12O8N2.2H2O (EDTA), Mac du co motso han che, oi khi ngi ta cung dung Na2CO3 khan, NaCl, vi vai tro chat

chuan goc.III.3. Yeu cau oi vi cac phan ng trong hoa phan tchPhan ng gia cau t X can xac nh vi DD thuoc th C phai hoi u cac ieukien sau ay:

1. Xay ra tc thi;2. Xay ra hoan toan theo chieu mong muon;3. Co he so xac nh va cho san pham co thanh phan xac nh;4. Co dau hieu ac trng e nhan biet luc phan ng cham dt.IV. CAC GIAI OAN CUA MOT PPPT

Mot qua trnh phan tch thng bao gom cac giai oan sau ay:IV.1. Giai oan chon mauMau phan tch co the la nguyen lieu, nhien lieu, ban thanh pham hoac thanhpham, co the ong goi hoac khong ong goi. dang nguyen lieu co quangmo, at a; nhien lieu co than, dau mo; ban thanh pham hay thanh phanrat a dang bao gom hoa chat (NaOH, Na2CO3, Na2SO4, NH4Cl,); san phamhoa hoc (xa phong, kem anh rang, DD xi ma,); thc pham (ru, bot ngot,ng, nc cham, dc pham, dc lieu (dch truyen, vitamin).

Giai oan chon mau rat quan trong v t ket qua phan tch mot lng

mau gii han, ta phai ket luan ve chat lng cua lo mau ln. Do o, lng mauphan tch phai c chon ung cach mi am bao tnh ai dien cua lo hang.Neu khong, viec phan tch ch gay hao ton vo ch, oi khi vi ket luan sai lechdan en nhng nguy hai tram trong.

Mau phan tch c chon t lo ong goi hay khong ong goi theo trnht sau:1. Chon mau rieng: mau rieng c chon ngau nhien mot so n v bao goi(neu lo ong goi) hay t mot so v tr khac nhau trong lo khong ong goi (ac tron kha ong nhat).2. Chon mau ban au: la mau ai dien c chon t cac n v ong goi haycac v tr khac nhau cua mau rieng (khong ong goi). Tong lng mau ban auc goi la mau chung.3. Chon mau trung bnh th nghiem: mau chung c nghien nho, ray vi chat phu hp vi PPPT va tron eu.

Mau trung bnh th nghiem c chia lam ba phan bang nhau: ni giaohang gi 1 phan, ni nhan hang gi mot phan va phan con lai ni phan tchgi. Moi phan u tien hanh tat ca cac th nghiem can thiet vi moi th nghiemlam ba lan.

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Neu mau chung khong u ln e tao mau trung bnh th tang o ln cuamau ban au hoac tang so mau rieng. Neu mau chung qua ln co the giammau i bang cach loai bt nhieu lan, moi lan giam phan na theo nguyen tacxen ke (trai mau chung len khay tron hoac vuong thanh lp mong, chia lam 4,

8 hoac 16 phan. Lay cac phan trong cac o co cung so chan hoac cung so le,chuyen sang khay khac va tiep tuc thc hien viec loai bt mau chung bang

phng phap tren).IV.2. Giai oan chuyen mau thanh DDDang mau thch hp cho a so PPPT la dang DD. Co hai cach chuyen

mau hoan toan thanh dang DD phan tch.Phng phap tMau c hoa tan trong dung moi thch hp. Dung moi co the la nc cat, DDacid hay baz vi nong o thch hp:

- Nc cat hoa tan cac muoi NaCl, KNO3,- DD HCl: c s dung hoa tan mau CO32-, PO43-, SO32-, S2-,- DD HNO3: hoa tan PbS, CuS, As2S3, Hg2SO4, cac loai hp kim- DD H2SO4 2000C co the hoa tan c thep khong g. - DD HF: hoa tan SiO32-, SiO2, H2SiO3.Phng phap kho

Nhieu hp chat cua Al2O3, Fe2O3, TiO2, Cr2O3, ZrO2 kho tan trong cac dungmoi tren. Ta co the chuyen chung sang dang DD bang cach nung kho chungvi hoa chat ran nh: NaOH, Na2CO3, K2S2O7, Na2O2, Na4BB4O7 500 1000 C

trong lo nung. Mau va chat nung c cha trong chen bang Pt hay Ni. Cau tc chuyen thanh muoi de tan, sau o c hoa tan bang dung moi thch hp.

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Du chuyen mau thanh DD theo phng phap nao cung phai am baocac yeu cau nh khong c lam mat mau trong qua trnh hoa tan; khong lamban mau (a them cau t la) khi hoa tan.IV.3. Chon phng phap thch hp va thc hien phan ng

Phng phap thch hp la phng phap co o nhay, o chon loc, toc ophan tch cao va cho ket qua gan vi ket qua thc. Sau khi chon c phngphap thch hp, thc hien phan ng gia DD mau phan tch va thuoc th theonhng ieu kien xac nh. Quan sat cac dau hieu ac trng xuat hien khi phanng xay ra (nh tnh) hoac o the tch hoac can khoi lng hp chat tao ra(nh lng).IV.4. Kiem chng ket qua va x ly ket qua phan tch

oi vi PPT, ngi ta co the kiem chng lai ket qua bang nhng phanng ac hieu khac. Neu la PTL, ngi ta tnh ket qua phan tch da vao cacd kien ghi nhan c va bieu dien ket qua phan tch theo cac yeu cau cuaphng phap thong ke.

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CHNG 2. KHAI NIEM VA NH LUAT C BAN DUNG TRONGHOA PHAN TCHI. DUNG DCH NONG O DUNG DCHI.1. Dung dch: la he ong the do s phan tan cua phan t hay ion, bao gom haihay nhieu chat ma thanh phan cua chung co the thay oi trong mot gii hanrong. He gom chat phan tan (chat tan) dang ran, long, kh (R, L, K) va moitrng phan tan (dung moi) cung co the dang R, L, K.

Tuy trang thai tap hp cua chat tan va dung moi, ta co cac loai DD R/Rnh hp kim, DD R/L nh ng trong nc, DD L/L nh ru trong nc, DDR/K nh bui trong khong kh va DD L/K nh sng mu Trong hoa phan tch,hai loai DD thng gap pho bien nhat la R/L hoac L/L.I.2. Nong o cua DD

Cach bieu dien nong o cua DDNong o DD phu thuoc vao chat tan co trong mot lng dung moi xac

nh. Ngi ta phan biet:- DD loang: lng chat tan chiem t le nho- DD am ac: lng chat tan chiem t le ln- DD bao hoa: DD cha chat tan toi a ( t0C, P xac nh)- DD qua bao hoa: c tao thanh khi un nong DD bao hoa trong s

hien dien cua chat tan va lam nguoi t t DD thu c. Trang thaibao hoa la trang thai kem ben, ch can lac, khuay hay them mot ttinh the chat tan, lng chat tan d trong DD se lap tc tach ra tra vetrang thai bao hoa ben vng.

Nong o cua DD thng c bieu dien thong qua cac ai lng:m(g): khoi lng chat tan (co phan t khoi M)q (g): khoi lng dung moiVx (ml): the tch chat tanV (ml): the tch DD nhan c khi hoa tan m(g) chat tan hay Vx (ml)chat tan vao q (g) dung moi

d (g/ml): khoi lng rieng cua DD tao bi m (g) chat tan va q (g) dungmoi.Cac loai nong o c s dung trong hoa phan tch thng la cac

nong o sau ay:o tan la lng chat tan trong DD bao hoa t0C va ap suat nhat nh,

thng bieu dien bang so gam chat tan /100g dung moi:

S= 100xq

m

Nong o khoi lng hay nong o g/l: bieu dien so gam chat tan co trong

1 lt DD

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Hoa phan tch

Nong o ng lng: e bieu dien so ng lng chat tan trong 1 lt DD,ngi ta s dung nong o ng lng CN. ay la nong o c s dung nhieunhat trong hoa phan tch e tnh toan vi :

CN =(mx1000)/(xV)

Vi la ng lng gam cua chat tan.ng lng: ng lng cua mot nguyen to hay mot hp chat la sophan khoi lng cua nguyen to hay hp chat ket hp hay thay the va u vimot n v ng lng (co gia tr bang 1.008 phan khoi lng cua H 2 hay 8phan khoi lng cua O2), hoac mot ng lng cua mot nguyen to hay hpchat khac.ng lng cua mot nguyen to: Nguyen to X (nguyen t khoi MX) trong cachp chat se co ng lng gam X = MX/n; vi n la so hoa tr cua X trong hpchat.

V du : nguyen to N co ng lng N bang 14/1 trong N2O, bang 14/2 trongNO, bang 14/3 trong N2O3, bang 14/4 trong NO2 va bang 14/5 trong N2O5.

ng lng cua mot hp chat: Hp chat AB (phan t kho MAB) cong lng gam AB = MAB /n vi n la so n v ng lng tham gia phanng, thay oi theo tng phan ng ma AB tham gia.1. AB la chat oxy hoa hay chat kh: ng lng cua AB la lng AB co khanang cho hay nhan 1 mol ien t. Do vay, n la so ien t trao oi ng vi 1mol.V du:

2 KMnO4 + 10 FeSO4 + 8 H2SO4 2 MnSO4+ K2SO4 + 5 Fe2(SO4)3 + 8 H2OKMnO4 = MKMnO4/52. AB la acid hay baz : ng lng cua AB co kha nang cho 1 mol H+ hay 1

mol OH-. Nh vay, n la so ion H+ hay OH- co trong 1 mol chat (thc s thamgia phan ng). Vi cac phan ng trung hoa hoan toan:

HCl = M/1; H2SO4 = M/2; H3PO4 = M/3NaOH = M/1; Ca(OH)2 = M/2; NH3 = M/13. AB la hp chat ion hay muoi: ng lng cua AB la lng AB co kha nang

trao oi vi mot mol ion mang ien tch 1+ hay 1-:BaCl2 = M/2; NaCl = M/1; FeSO4 = M/2; Fe2(SO4)3_= M/64. AB la phc chat: Neu AB la phc chat [MLX]n+ tao thanh bi ion kim loai

Mn+ (thng la nguyen to kim loai chuyen tiep, tc co phu tang d cha lap ayien t) vi cac ligand L (nguyen to hoac nhom nguyen to co cac electron tdo) theo phan ng:

Mn+ + x L [MLX]n+

ng lng cua phc hoac cac thanh phan cua phc c xac nh giongng lng cua muoi hoac hp chat ion.V du: Cu2+ + 4 NH3 [Cu(NH3)4]

2+

Cu2+ = M/2; [Cu(NH3)4]2+ = M/2

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Hoa phan tch

Nong o cua DD sau khi pha tronTron DD a% vi DD b% (cua cung mot chat) se c DD c% vi a>c>b neua>b.Ty le pha tron c xac nh bang quy tac ng cheo:

a (c-b) = ma

c tc ma/mb =ca

bc

b (a-c) = mb

Lien he gia cac nong o thong dung

T CM =V

x

M

m 1000 ; CN =(mx1000)/(xV) ; C% = 100xmq

m

+

, ta co:

Cg/l = CM*M = CN*Cac nong o con lai da tren nh ngha, co the chuyen oi rat de dang tnong o nay sang nong o kia va ngc lai:

CM =M

dxC 10% ; CN = (C%*10d)/

CN = n*CM

M =1000

xMxVCM = (CN**V)/1000 =

100

)%( mqC +

II. NH LUAT TAC DUNG KHOI LNGKhi cho cac chat tac dung vi nhau, co nhng phan ng hoa hoc xay ra

hoan toan, ngha la toan bo cac tac chat phan ng het vi nhau e tao thanhsan pham.V du: 2 H2 + O2 2 H2O

Trong thc te, a so cac phan ng thng gap lai la thuan nghch, ngha la cacphan ng dien ra khong en cung ma ch dien ra en trang thai can bang, trongo co s ton tai song song gia san pham va tac chat.

V du: H2 + I2 2 HITheo nh luat tac dung khoi lng, ty so gia tch hoat o san pham tren tchhoat o tac chat la mot hang so, c goi la hang so can bang K.nh luat tac dung khoi lng ap dung cho phan ng thuan nghch tong quat:

aA + bB cC + dD

K =ba

dc

BxA

DxC

)()(

)()(

Neu DD loang:

K= badc

BxADxC

][][][][

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Hang so can bang K cho biet phan ng a chon dien ra vi mc o nao:K cang ln, phan ng thuan (1) cang chiem u the va ngc lai K cang nho,phan ng nghch (2) cang chiem u the. Tuy nhien, can bang at c la can

bang ong nen khi co s thay oi mot trong cac yeu to nh: nong o, ap suat,nhiet o th can bang se thay oi goi la s dch chuyen can bang. S dchchuyen nay c xac nh theo nguyen ly Le chatelier (khi cac yeu to benngoai nh nhiet o, ap suat, tac ong len he, can bang se dch chuyen theochieu hng chong lai s thay oi).

Phng trnh K=ba

dc

BxA

DxC

][][

][][ ch hoan toan nghiem ung oi vi DD ly

tng. Vi cac DD thc, phng trnh nay co the ap dung kha ung vi cacchat khong ien ly hoac cac chat ien ly yeu trong cac DD nc loang va hoan

toan khong the ap dung oi vi chat ien ly manh (kiem, acid manh, muoi)hoac cac chat ien ly yeu trong cac DD am ac co dung moi la nc.

III. NH LUAT TAC DUNG NG LNGnh luat tac dung ng lng c Daton phat bieu nh sau:

Trong mot phan ng hoa hoc, so ng lng gam cua cac chat tham gia phanng phai bang nhau. Noi cach khac, trong mot phan ng hoa hoc, mot nglng gam cua chat nay ch thay the hay ket hp vi mot ng lng gamchat khac ma thoi.

Xet phan ng: A + B C + DGoi mA, mB: khoi lng cua A,B nguyen chat tac dung va u vi nhau (g)BA, B: ng lng gam cua A, BBVA, VB: the tch cua A, B tac dung va u vi nhau (ml)CA, CB : nong o ng lng gam cua DD A, BAp dung nh luat tac dung ng lng oi vi tac chat A, B (so ng lngcua A bang so ng lng cua B), ta co:

B

B

A

A

D

m

D

m= hay

B

A

B

A

D

D

m

m=

va VAxCAx10-3

= VBxCB

Bx10-3

hay VAxCA = VBxCB B

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CHNG 3. PHNG PHAP PHAN TCH KHOI LNGPhng phap phan tch khoi lng la mot trong nhng phng phap nh

lng co o chnh xac rat cao (co kha nang at ti 0.01%) nen thng c sdung lam phng phap trong tai. Tuy nhien, cac nhc iem cua phng phap(thao tac phc tap, ton nhieu thi gian,) a lam cho phng phap nay hanche khi a vao s dung trong thc te, neu chon c phng phap khac thchhp hn.I. NGUYEN TAC:

Phan tch khoi lng la phng phap nh lng cau t X da tren phepo khoi lng. Viec thc hien co the tien hanh theo nhieu phng phap khacnhau:

Phng phap trc tiepX c tach di dang n chat hay hp chat ben, t tan khoi mau va em can:

AX A + XV du 1: nh o tro cua mot chat: nung chat can xac nh o tro nhiet othch hp cho en khi lng tro con lai at khoi lng khong oi. Can lng trose xac nh c o tro.V du 2: nh lng vang trong mau hp kim: hoa tan hp kim co cha vang

bang nc cng thuy, thu c DD cha ion vang va cac ion khac. ThemH2O2 vao DD, ion vang c kh thanh vang nguyen to trong khi cac ion con

lai khong b anh hng. Vang c tach khoi DD, ra sach va can.Phng phap gian tiepX c tach di dang hp chat de bay hi ra khoi mau, can mau trc va saukhi tach: AX A + X Phng phap nay dung e xac nh o am hoac nc ket tinh cua mau, hoacham lng chat kh trong mau nao o (v du ham lng CO2 trong mau a voi).Phng phap gian tiep con co the la phng phap xac nh cac kh nh CO2,O2, CO, bang cach hap thu chat can xac nh vao mot hoa chat thch hp ;can chat nay trc va sau khi hap thu se suy ra lng chat can xac nh.Phng phap ket tuaHoa tan mau e chuyen X thanh ion trong DD; dung thuoc th C ket tua va

tach X di dang hp chat t tan CX roi can CX:AX A+ + X-

X- + C+ CX V du: muon xac nh ham lng Ba2+ trong mau BaCl2.2H2O, hoa tan mau vadung DD H2SO4 ket tua thanh tinh the BaSO4, ra sach tua, say (nung) va canBaSO4.

Trong cac phng phap phan tch khoi lng, PPPT ket tua ong vai tro quantrong va c ng dung rong rai nhat. Du bang phng phap nao trong cac

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phng phap, t lng mau ban au xac nh va t khoi lng can c co thetnh ham lng cua X trong mau mot cach de dang.II. CAC GIAI OAN CUA PPPT KHOI LNG KET TUAPhng phap dung nhieu nhat la chuyen X thanh hp chat t tan. Ngoai cac

giai oan bat buoc oi vi 1 qua trnh PPL bao gom viec chon mau ai dien,can lng mau thch hp va chuyen mau thanh DD phan tch, can phai tienhanh cac giai oan sau:

- Ket tua cau t can xac nh di dang hp chat thch hp- Loc va ra tua- Chuyen dang tua sang dang can- Can

Can phai lu y khong che lng mau ban au e nhan c lng can thchhp:

- Tua tinh the 0.200 0.500g- Tua vo nh hnh 0.100 0.300gII.1. Tao tua:Chon dang tua va thuoc th thch hp

Chon thuoc th C thch hp e tao tua vi X:C + X CX

Yeu cau oi vi dang tua va dang canDang tua va dang can phai ap ng cac yeu cau sau ay:

1. Ben, t tan e tao tua c hoan toan. Phan ng ket tua c xem lahoan toan neu sau khi ket thuc phan ng o tan cua tua trong DD xap xo chnh xac cua can.

2. Dang tua phai co tinh the ln e t tan, de loc va ra.3. Tua co o tinh khiet cao, t hap phu hay nhiem ban. Thuan li nhat la

nen chon ket tua tinh the cang to cang tot.4. Tua co dang hp chat xac nh, co the chuyen hoan toan sang dang can

mot cach de dang.5. Dang can phai co s tng ng gia thanh phan va cong thc hoa hoc;

phai ben vi moi trng (khong hap thu CO2, khong b oxy hoa bi O2cua khong kh, khong b phan huy nhiet o cao).

Yeu cau oi vi thuoc thThuoc th c chon phai hoi u cac ieu kien sau:

1. Co tnh chon loc cao (ch tao tua vi cau t can xac nh).2. e phan ng hoan toan, thuoc th c dung tha t 10 50% hoac 200

-300% neu thuoc th de bay hi. Can lu y khi s dung cac thuoc thma lng tha co the lam tan tua.

V du: Al3+ + 3 OH- Al(OH)3 + OH- AlO2

- (tan) + H2OHoac HgI2 + 2 KI K2[HgI4] (tan)

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3. Lng thuoc th dung tha phai c loai bo de dang trong qua trnhloc, ra, nung tua.

4. Thuoc th co kha nang tao thanh dang can co ham lng cua nguyen tocan xac nh chiem ty le cang nho cang tot, bi ieu nay se giup giam

sai so do can.Chon ieu kien tao tua thch hpieu kien tao tua thch hp la ieu kien thc hien phan ng gia thuoc th Cva cau t X sao cho viec tao tua hoan toan; tua thu c tinh khiet va de locra. Muon c vay, ngoai viec phai quan tam en dang tua thu c, cacnguyen nhan co the gay ban tua, con can phai quan tam en cac yeu to co khanang anh hng en o ben cua tua nh pH cua moi trng, nhiet o cua DD,cac can bang phu co the lam tan tuaAnh hng do dang tuaKhi cho thuoc th vao DD cha ion cau t cho en khi DD qua bao hoa (tchnong o cac ion ln hn tch so tan cua tua) th bat au xay ra s ket tua. Giaioan au tien la mam ket tinh, c hnh thanh ch ch gom bon phan t nenkch thc rat be. Mam ket tinh ong vai tro trung tam tao ieu kien cho caccation va anion trong DD tiep tuc ket tua tren be mat, lam cho mam ket tinhphat trien thanh hat ket tua co mang li tinh the ba chieu, co hnh dang xacnh, c goi la ket tua tinh the. Mam c sinh ra nhieu hay t va ket tua taothanh co hat to hay nho phu thuoc vao o qua bao hoa cua DD:

o qua bao hoa =S

SQ

Trong o: Q: nong o cua cac thuoc th sau khi tron vao nhau, trcluc taomam (mol/l)

S: o hoa tan cua ket tua sau khi at can bang (mol/l)Nh vay, khi o qua bao hoa cang nho, toc o tao mam cang cham va

do o, cac hat ket tua de phat trien thanh hat to thanh. Cac ion c sap xeptren mang li tinh the tao nen cac hat ket tua co hnh dang xac nh, goi laket tua tinh the. Nhng ket tua co o hoa tan ln thng de tao tua tinh the.

Ngc lai, o qua bao hoa cua DD cang cao th toc o tao mam cang

ln. Neu o qua bao hoa ln, cac mam sinh ra mot cach o at, cha kp phattrien bao nhieu a lien ket vi nhau bang lc lien ket yeu, tap hp ngay thanhket tua. Cho them thuoc th va DD, qua trnh lai tiep tuc nh tren. Cac ionc sap xep hon on, khong nh hng nen c goi la ket tua vo nh hnh.Loai tua nay thng c tao thanh khi ket tua co o tan qua nho (lam cho obat bao hoa cua DD qua ln), v du nh cac ket tua sunfua va hidroxyt cua cackim loai nang. Tham ch, o qua bao hoa cua DD qua cao con co kha nang taothanh DD keo, cha cac hat rat be (la cac phan t khuyech tan bao gom 103 -104 nguyen t co kch thc 10A0 1000A0) va mang ien tch cung dau. Cachat nay khong b lang khi ly tam va b lot qua giay loc thng mot cach dedang. Neu them vao DD keo chat ien ly manh e trung hoa ien tch cua hat

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Hoa phan tch

keo, cac hat keo co ieu kien va cham vi nhau manh hn, nhieu hn se conhieu kha nang ket hp vi nhau thanh cac hat ln hn. Cac hat nay langxuong va tao thanh tua vo nh hnh. V vay ma co the noi rang tua vo nhhnh c tao thanh do s ong tu cua DD keo.

Tuy nhien trong thc te, khong co ranh gii ro rang gia ket tua tinh thevi ket tua vo nh hnh. Ngoai yeu to phu thuoc vao ban chat cua ket tua, stao thanh ket tua dang nay hay dang kia phu thuoc rat nhieu vao ieu kientien hanh tua. V du, BaSO4 c tao thanh t dung moi nc de tao thanh kettua tinh the nhng trong hon hp dung moi nc etanol (30-60% etanol) thlai de dang tao tua vo nh hnh.

Trong PPPT khoi lng, neu tua thu c la tua tinh the cang to cang deloc, ra va giam nhiem ban, tao ieu kien cho qua trnh xac nh cang thuanli. e at c ieu nay, ngoai cac bien phap c s dung e lam tang S va

giam Q nham muc ch lam giam o bat bao hoa cua DD trong ieu kien cothe, mot so bien phap khac cung c s dung e co the nhan c tua tinhthe co kch thc ln bao gom:

1. Tien hanh ket tua t DD loang, nong, rot them t t thuoc th vao DD,khuay eu e lam giam o bao hoa cuc bo cua DD. DD nong con giupgiam hien tng hap phu cac ion la gay ban tua va giup cho tua khongb tao thanh trang thai keo.

2. Tien hanh ket tua pH thap ( ieu kien nay, ket tua se tan nhieu). Saukhi tao tua xong, a DD ve pH thch hp co o tan cua tua thap nhat.

3. Sau khi tao tua, e yen mot thi gian nham tao ieu kien cho tua lnlen goi la lam muoi tua (20-30 phut hoac co the keo dai t 1-6 gi).Viec lam muoi tua thng c tien hanh nhiet o kha cao nhngtranh e DD soi bung. Trong thi gian nay, cac tinh the nho se tan ra,bam tr lai vao cac tinh the ln va lam tua ln len. Tuy nhien, can xemxet tng trng hp cu the e tranh cac sai so co the mac phai. V du,qua trnh hau tua co the xay ra khi keo dai thi gian lam muoi tua.

4. e tranh hien tng qua bao hoa, con co the dung phng phap ket tuaong the (hay con goi la ket tua trong moi trng ong tng) bangcach tao thuoc th t t trong DD phan tch qua mot hoa chat trung gianthay v cho thang thuoc th vao DD. V du, e ket tua cac hydroxyt kimloai, ngi ta s dung phan ng thuy phan ure (NH2)2CO khi un soiDD:

(NH2)2CO + H2O 2 NH3 + CO2NH3 sinh ra lam tang pH cua DD len t t tao tua hydroxyt kim loai

khong tan . Qua trnh ket tua ong the tao cho DD co o qua bao hoa rat thap,giup thu c ket tua tinh the co kien truc tinh the hoan chnh, tham ch oivi mot so ket tua von la ket tua vo nh hnh nh ket tua hydroxyt chang han.

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Neu trong ieu kien tao tua chac chan thu c tua vo nh hnh, egiam tap chat do tua vo nh hnh co dien tch be mat rat ln nen de hap phuchat ban, can tao tua trong ieu kien sau ay:

1. DD mau va thuoc th can nong va kha am ac e giam hap phu, tua txop, de lang.2. Thuoc th c them nhanh va khuay au e chat ban khong bam lentua.

3. Ngay sau khi tao tua, them ngay DD ien ly manh e pha lp ien tchkep tren be mat hat keo, lam tua de ong tu.

4. Them vao DD mot lng nc nong trc khi loc e tach tua ra khoiDD va lam giam nong o cau t la trong DD.

5. Tua c loc ngay e tranh phan ng phu. Neu tua de tan nhiet ocao th lam nguoi tua trc khi loc.

S nhiem ban ket tuaTrong thc te, ket tua luon luon co kha nang b nhiem ban do keo theo motso chat co mat trong DD. Hien tng nay goi la s cong ket (ket tua theo).Cac loai cong ket gay tac dung nhiem ban co the ke nh sau:1. Hap phu be mat: Hap phu la hien tng cac cau t la dang ion (do

thuoc th dung tha hoac do s co mat cua mot so chat ien ly khac)bam vao cau t chnh, xay ra manh khi cau t chnh dang keo haydang tinh the mn. Neu hap phu cac anion, ket tua se mang ien tch amva co kha nang hap phu tiep cac cation khac lam cho ket tua b nhiem

ban bi cac tua khac. Qua trnh hap phu be mat co tnh chon loc (utien hap phu cac ion co trong thanh phan ket tua hoac nhng ion cocung ban knh ion vi ket tua). V du, trong DD co cac ion I -, Cl-, K+,NO3

-, ket tua AgI se hap phu I- trc, sau o ti Cl- va hau nh khonghap phu NO3

-.Co the lam giam hien tng hap phu be mat bang cac bien phap:

a) Tao tua tinh the to hay giam dien tch be mat cua tuab) Tao tua nhiet o cao (v hap phu la qua trnh toa nhiet).c) Pha loang DD mau va thuoc th e lam giam nong o tap chat.d) Ra ket tua sau khi loc bang DD thch hp. Trong DD ra co mat

mot so chat ien ly co the hap phu canh tranh vi cac ion gaynhiem ban, va cac ion canh tranh nay se c tach ra khoi kettua mot cach de dang trong qua trnh x ly tiep theo. Cac chatien ly con co tac dung chong hien tng peptit hoa (tua vo nhhnh tr lai trang thai keo).

2. Noi cong ket: la hien gay nhiem ban ben trong hat ket tua, do mot sotua phu tua theo cung vi tua chnh. Hien tng noi cong ket bao gomba loai chnh.

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Hoa phan tch

a) Cong ket ong hnh: Cac v tr cua ion la thanh phan cua ket tua trong mang li tinh the b thay the bi ion khac, thng xay ravi cac ion co ien tch va ban knh giong nhau hoac gan giongnhau. V du, khi tao tua BaSO4 co mat Pb

2+, mot so ion Ba2+ trong

mang li tinh the cua BaSO4 b thay the bi mot so ion Pb2+

theocan bang:Ba2+(tt) + Pb

2+ Ba2+(dd) + Pb2+(dd)

Ch co the khac phuc hien tng cong ket ong hnh bang viec tienhanh ket tua lai.

b) Cong ket do s tao tua phu t mam tinh the cua tua chnh:Mot so hp chat khong tua trong ieu kien rieng le nhng lai tua khicung hien dien vi mot chat khac.V du: Fe2(SO4)3 tan nhng khi them thuoc th SO4

2- vao DD Ba2+ co

lan Fe3+, ta co hai phan ng tao tua:Ba2+ + SO4

2- BaSO4 2 Fe3+ + 3SO4

2- Fe2(SO4)3

Giam hien tng nay bang bien phap chuyen ion anh hng sang dangkhac, v du: Fe3+ Fe2+

(cong ket) (khong cong ket)Cung co the che Fe3+ di dang phc ben, v du nh [FeF6]

3+

c) Cong ket do tao thanh hp chat hoa hoc:Trong DD co Fe2(SO4)3, khi thc hien phan ng tao tua Ba

2+ bang

SO42-, ngoai phan ng tao tua:Ba2+ + SO4

2- BaSO4 Fe3+ co the tao phc vi SO4

2- thanh [Fe(SO4)2]-. Ion phc nay tac dung

vi Ba2+ tao thanh hp chat ben:Ba2+ + 2 [Fe(SO4)2]

- Ba[Fe(SO4)2]2 3. Cong ket do s hap lu: la hien tng ban b gi lai trong tua trong qua

trnh ln len cua tinh the ket tua. Tap chat b cong ket vao ket tua phanbo khong ong eu ma tap trung chu yeu nhng cho khuyet tat cuatinh the ket tua. V du khi cho DD BaCl2 vao DD H2SO4, ket tua BaSO4tao thanh hap phu ion SO42- len be mat cua no tao thanh lp hap phu.Do lp hap phu mang ien tch am, cac ion dng (ion oi) lai b happhu tiep theo. Khi cho tiep thuoc th Ba2+ vao, cac ion Ba2+ se ay cacion oi ra va tiep tuc tao thanh ket tua mi. Tuy nhien, neu cho nhanhBaCl2 vao th ket tua mi c tao thanh nhng cac ion oi lai cha bay ra het, ket qua la con mot so ion oi nam xen ke gia cac o mangtinh the cua ket tua. Bien phap giam hien tng hap lu la tao tua tDD loang, rot them t t thuoc th, khuay eu hoac ket tua t moitrng ong the.

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4. Cong ket hau tua: la hien tng cau t phu tua theo cau t chnh neutua chnh e lau trong DD. V du ZnS tua theo CuS , HgSneu trongDD co Zn2+. Giam hien tng nay bang cach loc, ra tua ngay.Cac anh hng khac

Khi ket tua trong DD co mat nhieu ion khac, o tan cua ket tua b tang lendo cac nguyen nhan:1. Cac ion H+, OH- hoac ion khac) tham gia can bang phu vi cac ion

thanh phan cua ket tua.2. Ngay ca khi khong tham gia can bang phu vi cac ion thanh phan cua

ket tua, o tan cua tua van co the tang len khi ket tua trong DD co matnhieu ion khac, do s hien dien cua nhieu ion lam tang lc ion trongDD, lam cho he so hoat o cua cac ion giam xuong va v vay lam tango hoa tan cua ket tua:

AB An+ + Bn-S S

TAB = [An+][Bn-].fAfB = S

2 S = )/( BAAB xffT

3. Theo bieu thc tch so tan, khi tang nong o cua thuoc th trong DD selam cho nong o cua ion trong ket tua giam xuong, tc la lam cho otan cua tua giam xuong. Tuy nhien, tang lng thuoc th cung ong thitang nong o cac ion trong DD va t o lai lam tang o hoa tan cua kettua. Trong nhieu trng hp, lng thuoc th dung tha lai con co khanang tao thanh phc vi ion ket tua va cang lam cho o tan cua tua btang len. Do o, lng thuoc th s dung phai c khong che sao choviec tao tua c thc hien hoan toan nhat.

4. Cac ket tua vo c (thng la hp chat ion) de tan trong dung moi phancc, con cac chat khong phan cc se de tan trong dung moi khong phancc. e lam giam o hoa tan cua cac ket tua trong nc (CaSO4,PbSO4), ngi ta thng them ru etylic vao nc.

5. o hoa tan cua ket tua ty le nghch vi ban knh cua hat ket tua, acbiet oi vi cac hat ket tua co sc cang be mat ln.

6. o tan cua ket tua phu thuoc kha ln vao nhiet o. a so qua trnh hoatan chat ran vao nc la qua trnh thu nhiet, do o, khi tang nhiet o selam cho ket tua tan nhieu hn.II.2. Loc va ra tua

Loc la bien phap nham tach tua ra khoi DD. Chon dung cu loc phu hplng tua va cach chuyen t dang tua sang dang can:1. Neu tua c nung nhiet o cao: dung phieu thuy tinh va giay loc hau

nh khong tro (lng tro sau khi nung t 3x10-5 5x10-5g). Giay loc cokch thc lo xop thay oi, thng gom 3 loai: lo xop mn, lo xop trung

bnh va lo xop kha ln, vo hop co mau khac nhau c qui c tuy theonha san xuat va c la chon sao cho tua khong chui c qua giay loc

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Hoa phan tch

ma thi gian loc khong qua cham. V du: c, giay loc bang xanhc s dung cho cac ket tua hat mn, giay loc bang vang dung cho kettua hat trung bnh va giay loc bang o dung cho ket tua hat ln hoac kettua vo nh hnh.

2. oi vi ket tua de b kh trong qua trnh ot chay giay loc hoac nung(do carbon cua giay) hoac neu tua c say di 2500C dung phieu thuytinh ca hoac hay chung loc gut. Mang loc la lp thuy tinh ca nho hay lpbot amiang. o mn cua mang loc cung c la chon phu thuoc vaokch thc tua.

Ra tua: la dung DD ra e lam sach tua. DD ra thng co cac ac iem:1. Nong (e tang qua trnh giai hap)2. Cha ion chung so vi tua chnh (e lam giam o tan tua)3. Co the cha lng nho acid hay baz e lam giam s thuy phan4. Can them chat ien ly thch hp e giam hien tng peptit hoa (tua

vo nh hnh sau khi ong tu tr lai dang keo). Thng dungNH4NO3 hay cac acid de bay hi khi chuyen sang dang can.

Thc ra, qua trnh loc va ra tua thng c tien hanh song song. Viecra tua c thc hien nhieu lan bang cach loc gan tua vi cac lngnho DD ra sao cho lng DD ra dung va u e lam sach tua nhngkhong lam tan tua va ton thi gian. Sau khi c tao tua va lammuoi trong coc, ket tua se lang xuong ay coc. au tien, gan phan DDtrong cho chay theo ua thuy tinh vao phieu loc. Khi phan ln chat long

a c loc qua phieu, lai ra tiep ket tua bang phng phap gan (rotmot t nc ra vao coc, khuay hon hp bang ua thuy tinh, e ket tualang xuong ay coc, gan phan nc trong vao phieu). Khi tua tngoi sach, tron tua vi nc ra va chuyen huyen phu vao phieu loc.Dung bnh tia nc cat xt that manh e keo phan tua a bam tren thanhvao coc. Neu cn, lau mat trong cua coc bang cac mau giay loc khongtro. Tiep tuc ra tua tren giay loc bang bnh tia. Nhap cac mau giay lauvao giay loc cha tua. Xep va chuyen toan bo giay loc vao vat cha tua(chen s, niken, thach anh hoac platin) em chuyen sang dang can.II.3. Chuyen sang dang can

Dang can la dang trc tiep c can, viec chuyen dang tua sang dang canc thc hien bang cach say hay nung, vi muc ch loai het nc happhu hoac nc ket tinh, hoac e chuyen hoan toan hon hp thanh hp chatxac nh:1. Say nhiet o di 2500C (neu ch can loai nc hap phu hay ket tinh).

AgCl: say 100 1300C2. Nung nhiet o 600 12000C tuy theo dang tua:

BaSO4 BaSO4 : 700 8000C (u chay giay loc)

Fe(OH)3 Fe2O3 : 9000C

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Al(OH)3 Al2O3 : 1000 11000C

CaC2O4 CaCO3 : (6000C) CaO (1000 12000C)

Thi gian say hay nung c la chon sao cho khi can, tua co khoilng khong thay oi. Sau khi say hay nung, e nguoi vat cha tua trong

bnh hut am roi mi can.II.4. CanCan dung e xac nh khoi lng dang can thu c la can phan tch (chnhxac 0.0001g hay hn na). Luon luon phai s dung phep can lap e xacnh khoi lng cua tua: b (vat cha tua) c say hay nung trc cungnhiet o se say va nung tua. e nguoi trong bnh hut am va can, c khoilng m0 (g). B cung tua c say (nung) e nguoi va can, co khoi lngm1 (g);

m1 = m0 + m Suy ra m = m1 m0

II.5. Tnh ket quaMau dang ran1. Can a(g) mau, bang PPPT khoi lng thu c m(g) cau t di dang

n chat hoac hp chat:a) Neu dang can cung la dang can tnh ham lng:X% = 100x

a

m

g

V du 1:T 0.3200g at, bang PPPT khoi lng th c 0.1200 g SiO2:

% SiO2 = 1003200.0

1200.0x = 37.50%

b) Neu dang can khac dang can tinh ham lng, s dung he sochuyen F e chuyen t khoi lng dang can sang khoi lngdang can tnh.:

F = xM

M

dangcan

dangtinh he so thch hp

V du 2: nh ham lng Si trong mau at v du 1 vi dang can

SiO2 la 0.1200g.Ta co: mSi = 22

SiO

SiO

Si xmM

M

= 1200.008.60

08.28x = 0.0561 g

Hay % Si = 10008.60

08.28

3200.0

1200.0xx = 17.53%

2. Can a (g) mau, hoa tan thanh V(ml) DD. T VX (ml) DD mau bang PPPTkhoi lng thu c m(g) cau t di dang n chat hoac hp chat:

% X = xFVV

xxa

m

xg100

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Hoa phan tch

Mau dang DD1. T Vx (ml) mau, bang PPPT khoi lng, thu c m(g) dang can:Cx(g/l) = m x F x

xV

1000

2. Lay V(ml) DD mau empha loang thanh V1(ml) DD (loang), lay Vx (ml)DD loang em phan tch khoi lng, thu c m(g) dang can:Cx (g/l) = m x F x

xVx

V

V 10001

III. NG DUNGIII.1. nh o am nc ket tinh chat de bay hi o tro va mat khi nungXac nh o am hoac nc ket tinhNguyen tac xac nh o am hoac nc ket tinh la say mau nhiet o thch hp(100 1100C e xac nh o am; 120 2000C neu muon xac nh nc ket

tinh) e uoi nc ra khoi mau cho en khi phan con lai cua mau co khoilng khong oi. Cach thc hien nh sau:

1. Say chen nhiet o thch hp en khoi lng khong oi, can c tronglng m0(g)

2. Cho mau vao chen vi lng mau t 1 - 10g, can c khoi lng m1(g)m1 = m0 + mmau

3. Say chen va mau en khoi lng khong oi, can c khoi lng m2(g)m2 = m0 + m (m: khoi lng mau kho, g)

% am = 100100)'(

01

21 xmm

mmx

m

mm

mau

mau

=

Xac nh chat bay hiThc hien tng t nh cach xac nh o am nhng nhiet o cao. V du exac nh ham lng CO2 trong mau a voi, nung mau 500 600

0C e uoiCO2 en khoi lng khong oi:Khoi lng b: m0(g)Khoi lng b + mau: m1(g) = m0 + mmauSau khi uoi CO2, can lai : m2 (g) = m0 + m

% CO2 = 100100)'(

01

21

xmm

mm

xm

mm

mau

mau

=

nh o tro hay chat mat khi nungThc hien tng t nh cach xac nh chat bay hi nhng nhiet o 600 -

8000C va o tro va chat mat khi nung c tnh tren mau a say kho:% o tro =(m2-m0)x100/(m1-m0)% chat mat khi nung =(m1-m2)x100/m1-m0(m1 = m0 + mmau vi m mau a say kho)III.2. nh lng bang cach tao tuaNgi ta co the s dung thuoc th vo c, hu c hoac dung phng phap taoanion trong moi trng ong tng e ket tua cac cau t can xac nh.

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CHNG 4. AI CNG VE PHNG PHAP PHAN TCHI. CAC KHAI NIEM LIEN QUAN EN PHNG PHAP PHAN TCH

Phan tch the tch la phng phap nh lng cau t X da tren phep o

the tch. Khi thc hien phan ng gia cau t X va DD chuan C, C thng ccha trong buret va c nho t t vao DD cha chat can xac nh X (Xthng c lay chnh xac bang pipet va cha trong erlen). Qua trnh tren cgoi la s nh phan hay phep chuan o. S chuan o se cham dt khi co tnhieu cho biet phan ng a ket thuc. T the tch thuoc th C ghi nhan c segiup xac nh nong o cua cau t X trong DD em chuan o.- Phan ng C + X A + B goi la phan ng chuan o- Thi iem C tac dung va het vi X goi la iem tng ng- e xac nh thi iem ket thuc chuan o, thng s dung mot hoa chat co

the tao nen s thay oi ghi nhan c tng ng vi thi iem o: DD oimau, xuat hien tua Thi iem ngng chuan o theo cac dau hieu ke trenc goi la iem cuoi. Hoa chat giup xac nh iem cuoi goi la chat ch th.Trong thc te, iem cuoi co the ung hoac khong ung vi iem tng ng.S chech lech gia iem cuoi va iem tng ng nhieu hay t tao sai sochuan o ln hay nho phu thuoc vao ch th a chon.

Trong PPPT the tch co the xac nh iem tng ng thong qua phepo mot so ai lng hoa ly nh ien the, o dan ien, mat o dong Cacphng phap nay c xep vao nhom PPPT dung cu.

Tuy ieu kien chuan o ma DD X co the c cha trong buret vathuoc th C c cha trong erlen.II. IEU KIEN CHUAN OTrong qua trnh chuan o phai tuan thu nghiem ngat nhng ieu kien e ambao cho viec phan tch c nhanh chong va at c o chnh xac cua phepnh lng (ngha la e thu c ket qua phan tch nh y muon).Di ay la mot vai ieu kien c ban nhat cua viec chuan o:

1. Ni chuan o phai c chuan b can than va co u anh sang ban ngayhay anh sang ien.

2. Cac dung cu em dung va cac may moc o phai ra sach va hieu chnhchnh xac trc khi chuan o.

3. Cac thuoc th em dung, cac chat phu a vao trong phan tch chuano, hon hp, nc cat hay nc trao oi ion phai khong co chat la, lamsai lech ket qua phan tch.

4. Trng hp oxy hay cacbon dioxyt co anh hng en qua trnh chuan oth tien hanh chuan o trong moi trng kh tr (thng la trong kh nit)e tranh nhng phan ng phu ma ta khong mong muon.

5.

Phai lac can than va lien tuc cac chat phan ng trong qua trnh chuan o(lac bang tay hoac bang may khuay c hay t).

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6. S chuan o phai hoan thanh trong khoang 5 10 phut va dien ra trongieu kien a c kiem tra nghiem ngat ve nhiet o, pH cua DD, s cohay khong co cua chat ch th, v.v... can thiet theo phng phap xacnh.

7. e xac nh iem cuoi cua qua trnh chuan o, chat ch th hay phngphap cong cu nao o c chon phai am bao xac nh ro rang va chnhxac iem cuoi va co kha nang trung vi iem tng ng.

8. Khi chuan o can am bao moi trng phan ng acid hay kiem bangcach them vao hon hp chuan o cac chat ien ly, cac dung moi hu chay cac tac nhan chiet, hon hp em, cac chat tao phc, cac chat xuctac, cac chat cam ng, cac chat ch th, v.v... can thiet theo phng phapxac nh.

9. o chuan cua cac DD chuan em dung trc khi chuan o phai cxac nh va kiem tra can than theo cac chat tinh khiet hoa hoc xac nh.

10.Tat ca nhng phep chuan o song song can lam trong cung mot ngay.Viec di cac phep xac nh song song sang ngay khac ch c pheptrong trng hp hoan toan toan tin tng vao o hang nh cua DDchuan dung e chuan o. Neu o chuan cua DD chuan khong hang nhth ngay hom sau lai phai kiem tra o chuan cua DD chuan.Y ngha cua phng phap phan tch chuan oChuan o la mot phng phap phan tch nh lng rat quan trong, no

c s dung rat rong rai trong thc te cac phong th nghiem cac nha may,

trng hoc va cav vien nghien cu khoa hoc e xac nh thanh phan cua cachp chat vo c, hu c va c nguyen to. Ngoai ra cac d kien nh lng thuc bang nhng phng phap chuan o con c dung e xac nh cau taochat nghien cu, nghien cu ong hoc cua cac qua trnh hoa hoc, xac nhhang so phan ly cua acid va baz, lc tng oi cua cac chat ien ly, o dai vav tr cua thang hang so t prton hoa cua cac dung moi khac nhau, e nghiencu s bien dang va s cng hoa cua cac phng phap tong hp ieu che cacnguyen to va cac hp chat ac biet tinh khiet, am bao o toi u cua cac quatrnh cong nghe hoa hoc, v.v...Phan loai cac phng phap phan tch chuan o

Tuy thuoc vao loai phan ng chnh c dung, ngi ta chia cac phngphap chuan o phan tch thanh cac nhom sau:- Phng phap trung hoa hay phng phap chuan o acid baz da ren phanng trung hoa cac acid, baz, muoi cua cac acid yeu hay baz yeu b thuyphan manh trong dung dch nc, cac hp chat vo c hay hu c trong DDkhong nc co tnh acid hay kiem, v.v...- Phng phap oxy hoa - kh da tren phan ng oxy hoa kh cua cacnguyen to co kha nang chuyen t mc oxy hoa thap len cao va ngc lai, cung

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nh cac ion va phan t phan ng c vi cac chat oxy hoa hoac kh makhong b oxy hoa hay kh trc tiep .- Phng phap ket tuada vao viec dung cac phan ng ket tua.- Phan ng tao phc da vao viec s dung phan ng tao phc, trong so cac

phan ng o, phan ng gia cac ion kim loai vi complexon c s dung rongrai nhat.III. CACH TNH KET QUA TRONG PHNG PHAP PHAN TCH THETCHIII.1. Nguyen tac chung: da vao nh luat ng lng. Vi phan ng chuano:

C + X A + BTai iem tng ng so ng lng cua C bang so ng lng cua X, tc:

CCVC = CXVX

Vi: CC, CX: nong o ng lng cua thuoc th C va cau t XVC, VX: the tch cua hai DD C, X (ml)III.2. Cac bieu thc tnhMau long: Khi mau dang DD, cac trng hp pho bien nhat co the gap nh

sau:1. Lay VX (ml) mau, chuan o bang VC (ml) DD chuan co nong o ng

lng CC:CN (X) = CC x VC/VX; CM (X) = CN (X)/nC(g/l) = CN x X = CN x MX/n

2. Lay V(ml) mau am ac pha loang thanh V1 (ml) DD loang; Dung VX(ml) DD loang chuan o bang VC (ml) DD nong o CC

CN (dd) = CCxV

Vx

V

V

X

C 1 C(g/l) = CN(dd) x X

Cung co the tnh trc tiep theo so ng lng DD chuan o:C(g/l) = CC x 10

-3 x VC x 1000 x V1 x X/(VX x V)Mau ran: Khi mau dang ran, chung ta co the gap cac trng hp sau:1. Can a(g) mau, hoa tan va chuan o bang VC(ml) DD chuan CC:

% X = CC x 10-3 x VC x 100 x X /a

2. Can a(g) mau, hoa tan va nh mc thanh V1(ml) DD loang; lay VX (ml)DD loang em chuan o bang VC(ml) DD chuan nong o CC:

% X = CC x 10-3xVC x

ax

V

V

X

1001 x X

Cac bieu thc tnh ket qua tren ch ap dung cho phng phap chuan o trctiep va chuan o the. Vi cach chuan o ngc, bieu thc tnh nh sau:

CCxVC = CX x VX + VC1xVC2 CX =X

CCCC

V

xVCxVC 11

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Hoa phan tch

Ngoai ra, con co the ap dung nh luat ng lng e tnh toan khi pha loangDD, da tren nguyen tac so ng lng trong hai DD am ac va loang bangnhau:

Cx V = C1xV1 V = V1xC1/C

(Co the ap dung cho ca hai DD tnh theo nong o mol)Trong mot so trng hp ac biet, viec tnh ket qua khong c tienhanh bang cach s dung cac bieu thc noi tren ma lai c tien hanh thongqua o chuan:

1. o chuan cua mot chat TX: So gam hay miligam chat X trong 1ml DD:TX (g/ml) = m/V hay T (mg/ml) = mx1000/V

2. o chuan theo chat xac nh TC/X: so gam hay miligam chat X tac dungva u vi 1 mililt DD chuan nong o CC:TC/X = CC x X/1000

CC = (1000 x TC/X)/ XV du: TC/X = THCl/NaOH = 0.00401g ngha la 0.00401 g NaOH se c tac dungva u vi 1 ml DD HCl 0.1N.

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CHNG 5. PHNG PHAP CHUAN O ACID BAZI. ACID - BAZI.1. nh ngha theo Arrhenius

+Acid la nhng chat khi hoa tan trong nc, phan ly cho ra H con baz lanhng chat phan ly cho ra ion OH.

V du:+HCl H + Cl

NaOH Na+ + OH

nh ngha Arrhenius n gian nhng co mot so mat han che nh sau:+- Khong ap dung cho mot so chat khi hoa tan trong nc cho ra H hoacOH-

mac du cong thc chat nay khong co cha H+

hoac

OH-

.V du: Dung dch cac muoi Al2(SO4)3 co tnh acid ro ret, con dung dch muoiNa2CO3 co tnh baz ro ret.

- Khong cho thay anh hng cua dung moi tren s ion hoa cac acid, baz. Khidung mot dung moi khac e hoa tan cac acid, baz, cng o cac acid, baz cothe thay oi han.

V du: HCl trong nc la mot acid manh nhng khi hoa tan trong aceton thHCl la mot acid yeu. nh ngha Arrhenius khong giai thch c vai tro cuadung moi trong s tao thanh H+ t cac acid.I.2. nh ngha theo BRONSTED

Acid la cac chat khi tac dung vi dung moi tao ra H+ +solvat hoa (H3O ).

Baz la cac chat co the nhan H+.

nh ngha Bronsted giai thch c tai sao muoi Al2(SO4)3 co tnh acidva muoi Na2CO3 co tnh baz.

Al3+ + 2H2O AlOH2+ + H3O

+

CO32 + H+ HCO3

Con co the viet la (CO32

lay H+

t nc ong thi cho ra OH

)CO3

2- + H2O HCO3 + OH

Mot acid Bronsted sau khi cho proton tr thanh mot baz goi la bazlien hp cua acid, va ngc lai mot baz Bronsted sau khi nhan proton cho raacid lien hp.

V du:

HCl co baz lien hp la Cl

CO32- co acid lien hp la HCO3

Mot cap acid baz lien hp co the bieu dien bang he thc:Acid baz + H+

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u iem cua nh ngha BronstedCho thay ro anh hng cua dung moi tren s tao thanh H+ hoacOH nh

o giai thch c anh hng cua dung moi tren cng o cac acid va baz.

Theo Bronsted Lowry, o manh cua mot acid the hien kha nang cho

proton, con o manh cua mot baz the hien kha nang nhan proton. Phan ngHCl + H2O H3O

- + Cl- +xay ra hoan toan: HCl la acid manh hn H3O va H2Ola baz manh hn Cl-. Noi chung acid cang manh bao nhieu, baz lien hp vino cang yeu bay nhieu.

Ngi ta thng chon H2O lam dung moi e nh lc acid hay baz.+O B + HAcid: A + H2 3O .

[A]

]O[B][HO][HK

O][H[A]

]O[H[B]K

aa

aaK

32

2

3

OHA

OHB

2

3

+

+

=

=

=

+

Vi dung dch loang

Ta co:+ay la mot hang so can bang cua phan ng phan ly ion H con goi la

hang so acid, ky hieu la K

][

]][[ 3

A

OHBKa

+

=

a.Hang so acid Ka cang ln (tc la ch so acid pKa cang nho) th lc acid

cang manh.

Vi cac acid a chc yeu, s ien ly xay ra qua nhieu giai oan.

V du:

H3PO4 + H2O = H2PO4- ++ H3O K1 = 7,51 x 10

-2 pK1 = 1,12

H2PO4- + H2O = HPO4

2- ++ H3O K2 = 6,23 x 10-8 pK2 = 7,21

HPO42-

+ H2O = PO43- +

+ H3O K3 = 2,20 x 10

-13

pK3 = 12,66-Baz: B + H2O A + OH

bb

2b

lgKpK

[B]

][A][OHO][HKK

=

==

V du: Amoniac co:

4,75pK,1,79x10K 33 NH5

NH==

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Anilin co:

Hang so baz Kb cang ln ( tc ch so baz pKb cang nho) th lc baz

cang manh

9,40pK,4x10K256256 NHHC

10NHHC ==

AB A + B

Vi A va B co the la ion hay phan t.[ ][ ][ ]AB

BAK = Theo nh ngha, hang so phan ly cua AB la:

Hang so phan ly cang ln, hp chat AB cang b phan ly manh, cang tben, do o K con c goi la hang so khong ben.

Neu K kha nho, ngi ta thng dung ai lng pK vi: pK = lgK

pK cang ln, K cang nho, AB cang t b phan ly.Vi mot acid yeu HA, ta co:

HA H+ + A-

aaa lgKpKva[HA]]][A[H

K ==+

Acid cang b phan ly (acid cang manh) khi Ka cang ln, pKa cang nho.

V du:HF co pKa = 3,2 nho hn pKa cua CH3COOH (pKa = 4,75), nen

HF manh hn CH3COOH.Xet baz cho phan ng can bang cang chuyen theo chieu thuan (cho

cang nhieu OH). e nh cng o cua baz ta dung hang so baz Kb vi:

K[A]

[HA].[OH]b =

He thc gia Ka va Kb: Ka.Kb = 1014

Hay pKa + pKb = 14

T he thc tren cho ta thay Ka cang ln (acid cang manh) Kb cang nho

(baz lien hp cang yeu).V du:

HF co pKa = 3,2 , pKb =14 3,2 = 10,8

HCN co pKa = 9,4 , pKb =14 9,4 = 4,6

CH3COOH co pKa = 4,75 , pKb =14 4,75 = 9,25

NH3 co pKa = 9,25 , pKb =14 9,25 = 4,75

Vi cac acid that manh nh HCl th baz lien hp Cl la baz vo cung yeu.+

Vi cac baz that manh nh NaOH th axt lien hp Na la acid vo cung yeu.

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I.3. Dung dch emDung dch em la dung dch tao thanh khi tron lan mot acid yeu (hoac

mot baz yeu) vi baz lien hp cua no ( hoac acid lien hp cua no).

V du: hon hp gom CH3COOH + CH3COO- hay hon hp gom: NH3 +

NH4+ -la hai hon hp em. Noi chung: HA + A hay B + BH+

Tnh chat:+ -HA + H2O H3O + A

+ -Khi them mot lng axit (H3O ), anion A ket hp vi no cho acid yeuHA. Trai lai, khi them OH-, acid HA ien ly cho H3O

+ trung hoa OH- cho bazyeu H2O.Ket luan: pH dung dch em thay oi rat t khi them mot lng axit hoac baz.II. Cach tnh pH cua cac dung dch acid, baz, muoi, dung dch em

Thang pH+Vi nhng dung dch acid hay baz loang, nong o H hoac OH hoac

OH rat nho, e co nhng con so de s dung hn, ngi ta thng dung cac ailng pH va pOH c nh ngha nh sau:

pH = - lgCH+ va pOH = - lgCOH

pH + pOH = 14

Khi tnh acid cua dung dch giam dan [H+] giam, [OH] tang, pH tang dan. Ta

co mot dai gia tr cua pH goi la thang pH c gii han t pH = 0 en pH = 14.+Trong nc nguyen chat [H ] = [OH] = 107 pH = 7

Trong dung dch axt [H+ ] > [OH ]+[H ] > 107 pH < 7

+ Trong dung dch baz [H ] < [OH ]+[H ] < 107 pH > 7

Vay pH = 7 la ranh gii gia cac dung dch acid va dung dch baz.

0 7 14

Dung dch bazDung dch acid

Cong Thc Tnh pH cua dung dch: (dung moi nc)- Nc nguyen chatpH = lg [H3O

+] hay pH = lg [H+] = 7- Dung dch acid manh: Vi Ca 106 M[H

+

] = CapH = lgCa

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- Dung dch baz manh: Vi Cb 106 M[OH] = CbpOH = lgCbpH = 14 pOH = 14 + lg Cb- Dung dch acid yeu: Vi Ka kha nho (acid kha yeu) Ca kha ln.pH =

2

1(pKa lgCa)

- Dung dch baz yeu: Vi Kb kha nho (baz kha yeu) Cb kha ln.pH = 14

2

1 (pKb lgCb)

- Dung dch muoi+ Muoi phat xuat t acid manh va baz manh

o la trng hp cac muoi loai NaCl, KNO3.

pH cua dung dch muoi nay chnh la pH cua nc nguyen chat co pH = 7.

+ Muoi phat xuat t acid manh va baz yeu

V du: Tnh pH dung dch NH4Cl 0.1M co Kb =10 4,75

Muoi nay gom cation NH4+ co tnh acid yeu va Cl co tnh baz vo cung

yeu vay dung dch muoi NH4Cl co the xem nh ch cha acid yeu NH4+ va ta

co the tnh pH dung dch muoi NH4Cl nh trng hp dung dch mot acid yeuthong thng.

2

1

2

1(pKTa co: pH = a lgCa) = ( 9,25 + 1) = 5,12

2

1

2

1Hoac: pH = (pKH2O pKb lgCM) = ( 14 4,75 + 1) = 5,12

+ Muoi phat xuat t acid yeu va baz manh

V du: Tnh pH dung dch CH3COONa 0,05M co Ka = 10 4,75

Muoi nay gom cation Na+ co tnh acid vo cung yeu (Ka = 0) v la acid lienhp cua NaOH baz that manh va anion CH3COO

co tnh baz yeu vay co the

xem dung dch nay nh ch cha baz yeu vay co the xem dung dch baz yeuthong thng.

2

1

2

1Ta co: pOH = (pKH O pK2 a lgCM) = ( 14 4,75 + 1,3) = 5,275

2

1

2

1Hoac: pH = 14 (pKb lgCb) = 14 (9,25 + 1,3) = 8,725

- Dung dch em+ Dung dch co moi trng acid

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b

a

aC

CK

+[H ] = Vi Ca: nong o acid

b

a

aC

CpK lg CpH = b: nong o baz

Ka: hang so can bang acid

+ Dung dch co moi trng baz .

[OH] =a

b

bC

CK

pH =14 p[OH] =

a

b

bC

CpK lg14

III. Noi dung phng phap chuan o acid bazPhng phap chuan o acid baz la phng phap nh lng cau t Xdang M(OH) bang thuoc th C dang HA hoac ngc lai:

HA + M(OH) MA + H2O

Tai iem tng ng, pH cua DD do muoi sinh ra quyet nh. Bc nhay cuang chuan o co o dai phu thuoc o manh, yeu va nong o cua acid bazs dung. iem cuoi c xac nh bang ch th mau acid baz (hay con goi lach th pH).IV. Cac phng phap chuan o acid baz thong dungIV.1. Chuan o acid manh bang baz manhV du: Chuan o HCl bang NaOH- Phan ng chuan o: H+ + OH- H2O

- Tai iem tng ng: [OH-] = [H+] pHt = 7

- Bc nhay cua ng chuan o kha dai: vi CHCl, CNaOH ~ 0.1N, bc nhayt pH = 4 en 10 co the chon cac chat ch th pH co s chuyen mau trongkhoang pH nay. Mot so ch th acid baz thong dung thng dung nh sau:

Ten ch th Khoang chuyenmau

Mau dang HIn Mau dang In

Phenolphtaleion 8.2 -10 Khong mau Tm

Bromothymolxanh

6.0 7.6 Vang Xanh

Bromocresol luc 3.8 5.4 Vang Xanh

Metyl da cam 3.1 4.4 Hong cam Vang

Metyl o 4.2 6.2 o Vang

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Hoa phan tch

Hnh 5.1: ng chuan o acid manh bang baz manhIV.2. Chuan o acid yeu bang baz manhKhi chuan o acid yeu HA bang baz manh

V du chuan o CH3COOH bang NaOH

- Phan ng chuan o: HA + NaOH NaA + H2O

- Tai iem tng ng: pH cua DD do NaA quyet nh la mot baz yeu conong o CNaA nen pHt c tnh:

pHtd = 7 + pKHA + lgCNaA

CNaA la nong o NaA sinh ra, ve mat ly thuyet chnh la nong o acid ban auhoac nong o acid ban au hoac nong o baz a tac dung, nhng thc te bgiam xuong do the tch DD tang len.

Bc nhay cua ng chuan o nam trong vung baz nen chon ch th copHch/m >7, thng dung phenolphtalein.

Hnh 5.2: ng chuan o acid yeu bang baz manh

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IV.3. Chuan o baz yeu bang acid manhChuan o baz yeu A- bang acid manh

V du: chuan o NH4OH bang HCl

- Phan ng chuan o: A- + HCl HA + Cl-

- Tai iem tng ng, pH cua DD c quyet nh bi HA la mot acid yeunen pHt c tnh: pHt: pKHA - lg CHA- Bc nhay cua ng chuan o nam trong vung acid nen chon ch th copHchuyen/mau < 7, thng dung metyl da cam, bromocresol luc, metyl o.

Hnh 5.3: ng chuan o baz yeu bang acid manhIV.4. Chuan o mot a acid (hoac nhieu n acid) bang baz manhNeu a acid co ka1, ka2,, kan khac kha xa nhau ( pK 4) va moi ka khongqua be (>10-10) th co the chuan o lien tiep tng chc vi ch th thch hp nhkhi chuan o tng n acid.

V du: chuan o H3PO4 bang NaOH:

H3PO4 + NaOH NaH2PO4 + H2O Ka1 = 10-2.12

NaH2PO4 + NaOH Na2HPO4 + H2O Ka2 = 10-7.21

Na2HPO4 + NaOH Na3HPO4 + H2O Ka3 = 10-12.38

pH tng ng c tnh gan ung nh sau:

pHt1 = (pKa1 + pKa2) = 4.66

pHt2 = (pKa2 + pKa3) = 9.8

Co the xac nh hai iem cuoi bang hai ch th:

- Bromocresol luc Vt1- Phenolphtalein Vt2Vt2 = 2 Vt1

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Hoa phan tch

Vt2 la the tch OH- dung e chuan o hai chc (khong chuan o c chc th

ba do Na2HPO4 la acid qua yeu).

Hnh 5.4: ng chuan o H3PO

4bang NaOHIV.5. Chuan o mot a baz (hoac nhieu n baz) bang acid manh

Cung nh a acid, neu a baz co kb1, kb2,, kbn khac kha xa nhau ( pK 4)Va moi k

b khong qua be (>10-10) th co the chuan o lien tiep tng chc vi ch

th thch hp nh khi chuan o tng n baz.

V du: Chuan o DD Na2CO3 bang HCl

CO32- la baz lien hp cua diacid H2CO3 (Ka1 = 10

-6.35; Ka2 = 10-10.32)

Na2CO3 + HCl NaHCO3 + NaCl

NaHCO3 + HCl H2CO3 + NaClH2CO3 CO2 + H2O

pHt1 = (pKa1 + pKa2) = 8.33

pHt2 ~ 4 (tuy thuoc vao nong o H2CO3 trongDD)

Co the xac nh hai iem cuoi bang hai ch th:

- Phenolphtalein Vt1- Metyl da cam Vt2

Vt2 = 2 Vt1 ; Vt2 la the tch HCl dung e chuan o hai nac.

Hnh 5.5: ng chuan o Na2CO3 bang HCl

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CHNG 6. PHNG PHAP CHUAN O OXY HOA KHCac phng phap chuan o oxy hoa kh thng c goi ten theo chat

oxy hoa dung lam chat chuan.Phng phap permanganatPhng phap permanganate (chuan o vi KMnO4) c s dung kha rong raitrong hoa phan tch. Phng phap chuan o nay co cac ac iem sau ay:

1. MnO4- la chat co tnh oxy hoa manh trong moi trng acid:MnO4

- + 8 H+ + 5 e- Mn2+ + 4 H2O E0 = 1.51V (a)

MnO4- + 4 H+ + 3 e- MnO2 + 2 H2O E

0 = 1.69V (b)Phan ng (a) thng c dung nhieu hn phan ng (b) v tao thanh Mn2+khong mau (de nhan iem cuoi). Mn2+ con co tac dung xuc tac giup cho

phan ng xay ra nhanh hn.2. MnO4- co mau hong ro trong DD nen con ong vai tro ch th giup nhan

biet iem ket thuc phan ng.3. Phng phap thng c dung e chuan o:

- Trc tiep cac ion co tnh kh nh Fe2+, (COO)22-, H2O2- Gian tiep cac ion co tnh oxy hoa nh Fe3+ (sau khi kh thanh Fe2+).- Chuan o ngc, v du hoa tan MnO2 bang lng (COO)22- tha va

chuan o lng tha (COO)22- bang MnO4

-.4. Cac nguyen nhan co the gay sai so he thong cho phng phap

permanganate:- DD MnO4- khong ben theo thi gian do

4 MnO4- + 2 H2O 4 MnO2 + 3 O2 + 4 OH

-

nen can chuan o lai e xac nh nong o khi dung.- Khong dung HCl tao moi trng H+ v co phan ng

2 MnO4- + 10 Cl- + 16 H+ 5 Cl2 + 2 Mn

2+ + 8 H2O- Nen dung H2SO4 loang tao moi trng- Phan ng cham nhiet o thng va khi cha co Mn2+ lam xuc tac.

Do o, thng chuan o nhiet o t0 600C va chuan that cham lucau.Phng phap dichromat

Phng phap dichromat (chuan o vi K2Cr2O7) cung c s dung kha rongrai trong hoa phan tch. Phng phap nay co cac ac iem sau:

1. Cr2O72- co tnh oxy hoa manh trong moi trng acid:Cr2O7

2- + 6 e + 14 H+ 2 Cr3+ + 7 H2O E0 (Cr2O7

2-/2Cr3+) = 1.33VCo the dung HCl, H2SO4 loang tao moi trng H

+

2. Chat ch th thng dung:Diphenylamin (E

0

i = 0.76V) hay diphenylamin sulfonat Ba (E

0

i = 0.85V)

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Hoa phan tch

Co mot vai trng hp ma E0i co the lech Et kha xa. Khi gap trng hpnay, co the dung hoa chat thch hp e keo dai bc nhay cua ng congchuan o e E0i nam trong vung bc nhay. V du, dung Cr2O7

2- chuan oDD Fe2+ se co Et > E

0i cua diphenylamine, do o, e keo dai bc nhay

trc iem tng ng can lam giam Ecb bang cach giam [Fe3+

], thngdung H3PO4 tao phc khong mau vi Fe3+.

3. Phng phap dichromat thng c dung e chuan o:- Trc tiep cac ion kh nh Fe2+- Gian tiep cac ion co tnh kh (SO32- , S2O32-, ) qua trung gian I2.Phng phap iod

Phng phap iod (chuan o vi I2) c s dung da tren cac ac iem:1. I2 co tnh oxy hoa trong moi trng gan trung tnh hay acid nhe

I2 + I- + 2e 3 I- (E0 = 0.545V)

2. Chat ch th la ho tinh bot tao hp chat mau xanh vi I 2 khi ch th conong o 2.10-5M (ch cho ch th ho tinh bot vao DD khi lng I2 con ratt trong DD, neu khong I2 se hap phu tren hat tinh bot gay sai so)

3. Phng phap thng dung chuan o:- Trc tiep cac DD S2O32-, Sn2+, SO32-, AsO33-- Gian tiep cac DD co tnh oxy hoa nh Br2, Cl2, MnO4-, Cr2O72-, ClO3-,

Cu2+, H2O2, Fe3+ bang cach cho DD muon chuan o tac dung vi

lng tha I-. Phan ng tao I2, chuan o I2 bang DD chuan S2O32-.

4. Cac nguyen nhan co the gay sai so he thong cho phng phap iod:- I2 rat de thang hoa nen DD kem ben, can chuan o trong bnh co

nap, pha loang DD va gi DD nhiet o thng (I2 ch tan trongnc dang phc I3

- do o can pha I2 trong lng KI thch hp).- Khi chuan o moi trng qua acid se pha huy ho tinh bot va co the

phan ng phu:S2O3

2- + 2 H+ H2SO3 + S - Neu moi trng qua baz co the tao phan ng phu:

I2 + 2 OH- I- + IO- + H2O

3 IO- 2 I- + IO3-

Phng phap bromatPhng phap bromat (chuan o vi BrO3

-) c s dung:1. Da vao kha nang oxy hoa manh cua BrO3- trong moi trng acid hoac

trung tnh2. Chat ch th thng dung: metyl o (ch th bat thuan nghch) trong moi

trng co [H+] = 2 N3. Phng phap thng c dung e chuan o trc tiep cac ion kh nh

As3+, Sb3+, Sn2+,3 As3+ + BrO3

- + 9 H2O 3 H3AsO4 + Br- + 9 H+

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Hoa phan tch

Phng phap ceriPhng phap ceri (chuan o vi Ce4+) c s dung

1. Da vao kha nang oxy hoa manh cua Ce4+Ce4+ + 1e- Ce3+ E0 (Ce4+/Ce3+) = 1.44V

2. Thng dung Ce4+ e chuan o NO2-3 Ce4+ + NO2- + H2O 2 Ce3+ + NO3- + 2 H+

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CHNG 7. PHNG PHAP CHUAN O TAO TUATrong phng phap chuan o tao tua, cau t X c chuan o bang

thuoc th C theo phan ng: C + X CX . Vi X la halogenur nh Br-,

Cl-, I-, thuoc th c dung la Hg+ hay Ag+ (Hg+ qua oc nen thng dung Ag+)va ch th c s dung co the la ch th tao tua (thng dung K 2CrO4), ch thhap phu (thng dung fluorescein) va con co the s dung ch th tao phc.

ieu kien cua mot phan ng tao tua:- Van toc phan ng ln e tao tua nhanh- CX phai co Tst nho (< 10-7 10-8)Cac phng phap chuan o tao tua thong dung gom co:Phng phap Mohr

Phng phap Mohr la phng phap chuan o trc tiep vi ch th tao tua

K2CrO4:1. Phan ng chuan o:

Ag+ + X- AgX2. Phan ng ch th:

2 Ag+ + CrO42- (vang) Ag2CrO4 (o nau) TAg2CrO4 = 10

-12

Tai iem cuoi, DD chuyen t mau vang ti (CrO42-) sang hong ao.

3. ieu kien chuan o:- Chuan o trong moi trng co pH = 6.5 10 (neu trong DD khong co

NH3) va pH = 6.5 - 8 (neu trong DD co NH3) v:

Neu pH < 6.5 co phan ng:2 CrO4

2- + 2 H+ 2 HCrO4- 2 Cr2O7

2- + H2ONeu pH > 10 co phan ng:2 Ag+ + 2 OH- 2 AgOH Ag2O + H 2ONeu co NH3 co phan ng:AgX + 2 NH3 [Ag(NH3)2]

+ + X-

- Chuan o nhiet o thng v Ag2CrO4 tan nhiet o cao- Lng K2CrO4 phai dung thch hp ([CrO42-] = 10-2M) e Ag2CrO4

xuat hien ngay sau iem tng ng ma mat co the nhan thay (luco [X]- con lai khoang 10-5 10-6M).Phng phap Fajans

Phng phap Fajans la phng phap chuan o trc tiep vi ch th hap phufluorescein

1. Phan ng chuan o:Ag+ + X- AgX

2. Phan ng ch th:AgX X- AgX AgX Ag +Fl- (mau hong nhat)

Mau DD tai iem cuoi: vang co anh huynh quang (fluorescein)

tua trangpht hong.

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Hoa phan tch

3. ieu kien chuan o:- pH DD 6.5 10 v neu pH < 6.5: Fl- + H+ HFl- [X-]010

-2M e lng AgX u nhieu cho phep nhan biet s chuyen maucua tua.

- e tua co be mat hap phu ln, can them vao DD chat bao ve keo AgXnh dextrin.Phng phap VolhardPhng phap Volhard la phng phap chuan o ngc vi chat ch th tao phcphen sat ba:

1. Cho lng tha Ag+ vao DD cha X:Ag+ + X- AgX

2. Lng Ag+ tha c chuan o bang SCN- vi ch th phen sat ba Fe3+:- Phan ng chuan o:

Ag+ + SCN- AgSCN (trang uc) TAgSCN = 10-12- Phan ng ch th:

Fe3+ + SCN- Fe(SCN)2+ (o mau)Mau DD tai iem cuoi: DD cha tua trang uc xuat hien mau cam nhat.

3. ieu kien chuan o:- pH < 3 e tranh tua Fe(OH)3 (dung HNO3 tao moi trng)- Neu chuan o Cl- bang phng phap nay, do TAgSCN < TAgCl nen co khanang xay ra can bang phu: AgCl + SCN- AgSCN lam tan tuaAgCl. Co the han che can bang phu tren bang cach loc AgCl trc khi

chuan o Ag+ tha, hoac un nong DD e AgCl ket von lai, hoac dungnitrobenzene e bao AgCl lai.

Ngoai cac phng phap chuan o tao tua noi tren, ngi ta con co the dungDD SCN- e chuan o trc tiep Ag+; dung DD Na2SO4 hoac DD K2CrO4 chuano trc tiep DD BaCl2; dung DD K2CrO4 chuan o trc tiep DD Pb

2+, Cacphng phap chuan o trc tiep nay cung c xep vao nhom phng phapMohr.

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CHNG 8. PHNG PHAP CHUAN O PHC CHATPhc chatPhc chat la nhng hp chat c cau tao t s ket hp gia:

Ion trung tam thng la ion kim loai ma phu tang d con trong (thng thuocnhom kim koai chuyen tiep)Ligand hay phoi t la nhng phan t hay ion cua nguyen to hay nhom nguyento vi nguyen to con ien t t do n.Ion trung tam va ligand noi nhau bang lien ket cong hoa tr hay lien ket phoitr. Phc chat co the dang ion hay phan t. Moi hp chat phc co the gom 1(goi la phc n nhan) hay nhieu ion kim loai trung tam (goi la phc a nhan)ket hp vi mot ligand (goi la phc n cang) hoac nhieu ligand (phc acang).

V du: Phc [Cu(NH3)42+Phng phap chuan o tao phcPhng phap chuan o tao phc thng c s dung e chuan o DD ion kimloai vi DD chuan la DD ligand tao phc vi ion kim loai theo can bangC + M MC (phc tan). e can bang co tnh nh lng, C c chon ephc MC co hang so ben kha ln. Nhieu loai ligand a c dung trongphng phap nay nhng thong dung nhat la etylene diamine tetraacetic acid(EDTA)HOOCCH2 CH2COOH

N-CH2-CH2 NHOOCCH2 CH2COOHEDTA dang acid khotan trong nc nen c dung dang muoi (2H+ cthay the bang 2Na+). Muoi nay co ten goi lacomplexon III hay trilon B ky hieula Na2H2Y hay H2Y

2- hay n gian hn Y4-. oi khi theo thoi quen ngi ta vangoi muoi la EDTA.NaOOCCH2 CH2COONa

N-CH2-CH2 NHOOCCH2 CH2COOH

EDTA

Tao phc vi kim loai theo can bang:

H2Y2- + Mn+ MY n-4 + 2 H+

ac iem cua phan ng chuan o s dung EDTA:

1. EDTA va ion kim loai tao phc theo ty le mol 1:12. Can bang tao ra H+, do o [H+] se anh hng en o ben cua phc. e

thc hien cac phan ng chuan o cu the thng s dung DD em pH tao

moi trng chuan o trong o hang so ben ieu kien u ln choyeu cau nh lng.MY

'

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Hoa phan tch

3. ieu kien cua phan ng chuan o:- Phc MY phai kha ben ( 10MY' 8) pH chuan o. Khi chon ch th

cho phan ng chuan o, phc tao bi ch th vi kim loai cung bennhng phai kem ben hn phc MY.

- Cac ion kim loai ton tai song song vi cau t chnh trong DD eu cokha nang tao phc ben vi EDTA gay anh hng tren ket qua xacnh. Co the loai bo cac anh hng nay bang cach tao dang tua benva loc khoi DD, hoac oi pH cua DD e lam phc phu kem benhoac dung hoa chat thch hp tao dang phc ben hn dang phc viEDTA.

- Can bang tao phc thng cham, do o can chuan o cham hay unnhe DD trc khi chuan o.

Cac phng phap chuan o phc chat (dung EDTA) thong dungnh lng Ca2+, Mg2+ hay hon hp Ca2++ Mg2+

1. Chuan o Mg2+: Mg2+thng c chuan o trc tiep pH = 10 vich th Erio-en-T:a) Phan ng chuan o: Mg2+ + Y4- MgY2-b) Phan ng ch th:

o Neu Mg2+ c cha erlen:MgIn + Y4- MgY2- + In

(Hong, tm) (xanh)DD chuyen t mau tm sang mau xanh

o Neu Mg2+ c cha buret:In + Mg2+ MgIn

(xanh) (Hong, tm)

DD chuyen t mau xanh sang mau tm

Khi chuan o Mg2+ trong DD khong c phep co mat Ca2+ vCa2+ cung tao phc ben vi EDTA pH = 10

2. Chuan o Ca2+:a) Chuan o trc tiep pH = 12.5, ch th calcon, murexide hay

Fluoresxon

Murexide (CaIn: o; In: xanh)

Fluoresxon (CaIn: vang luc huynh quang; In hong cam.)

Khi chuan o Ca2+, Mg2+ khong gay anh hng v [Mg2+] con rat tdo a tao tua Mg(OH)2, tuy nhien, lng Mg

2+ ban au khong che vtua Mg(OH)

2tao thanh nhieu qua se hap phu Ca2+.

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b) Chuan o pH =10, ch th Erio-en-T:Them vao DD mot lng MY2- trc khi them EDTA, do

< trong DD co can bang:MgY' CaY'

MgY2- + Ca2+ CaY2- + Mg2+

Lng Mg2+ sinh ra se tao phc vi ch th MgIn (hong, tm)

Khi chuan o bang EDTA, Ca2+ con lai tac dung trc:Ca2+ + Y4- CaY2-

Khi het Ca2+ t do, co can bang:Mg2+ + Y4- MgY2-Tai iem tng ng:MgIn + Y4- MgY2- + In

Dung dch co mau xanh cua In pH = 10.3. Chuan o hon hp Ca2+ + Mg2+:- Chuan o Ca2+ pH = 12.5 dung V1(ml) EDTA.- Chuan o tong Ca2+ + Mg2+ pH = 10, dung V2 (ml) EDTA

DD EDTA dung chuan o Mg2+ co the tch V2 V1 (ml).nh lng DD ch cha hon hp Fe3+, Al3+Da vao o ben khac nhau cua AlY- va FeY- moi trng pH khac nhau echuan o lien tiep Al3+ va Fe3+ trong hon hp.

1. Chuan o Fe3+: Chuan o trc tiep pH = 2.5 vi ch th acidsulfosalicylica) Phan ng chuan o: Fe3+ + Y4- FeY-b) Phan ng ch th: FeIn + Y4- FeY- + In

(tm) (vang nhat) (khong mau)Tai iem cuoi, DD chuyen t mau tm cua FeIn sang mau vang nhat cuaFeY-.c) ieu kien cua phan ng chuan o:- pH nay, phc AlY- khong ben ( =10FeY' 12.7, =10AlY' 4.2) nen Al3+

khong anh hng en phan ng chuan o.- Neu DD cha Fe2+, muon nh lng Fe tong, phai oxy hoa Fe2+

thanh Fe3+ (thng dung K2S2O8) roi mi chuan o v Fe2+ khong tao

phc ben vi EDTA.2. Chuan o Al3+: chuan o ngc pH = 5

a) Them vao DD (a chuan o Fe3+) lng tha xac nh DD Y4- pH=5. un soi DD ba phut tao ieu kien cho phan ng

Al3+ + Y4- AlY- ( =10AlY' 9.6) xay ra hoan toan.b) Chuan o lng Y4- tha bang DD kim loai M2+ (Cu2+, Zn2+, Pb2+) ch

th thch hp:

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P.A.N (CuIn: hong ; ZnIn: o; In: vang)Xylenol da cam (ZnIn: o; In: vang)Tai iem cuoi, DD chuyen t mau vang sang mau cam

c) ac iem:Dung phep chuan o ngc do phc AlY

-

ch hoan toan 800

C.- Neu khong chuan o Al3+ tren DD a chuan o Fe3+ ma chuan trenDD ban au, Fe3+ se anh hng v =10FeY' 14.2 (pH=5).

- e de nhn mau tai iem cuoi, thng dung them chat ch thbromocresol luc co mau xanh pH 5). S cong mau se lam qua trnhchuyen mau t vang chanh sang tm de nhan biet hn la chuyen tmau vang sang vang cam (e tranh sai tha, phai dng chuan o khiDD va chuyen sang mau tm).nh lng SO42- theo phng phap chuan o ngc

- Them vao DD lng tha xac nh Ba2+ co phan ng tao tua:Ba2+ + SO4

2- BaSO4 (trong moi trng ETOH e giam s tantua)

- nh lng Ba2+ tha bang cach chuan o trc tiep vi EDTA pH=10 ch th Erio en T hoac chuan o ngc bang lng thaxac nh EDTA sau o chuan EDTA tha bang Mg2+, ch th Erio en T.

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CHNG 9. PHNG PHAP CHUAN O IEN THE1. Nguyen tac: Phng phap chuan o ien the da tren viec o the cua

ien cc c nhung vao dung dch. Ga tr cua the phu thuoc vao nong

o cua cac ion tng ng trong DD.Th du, the ien cc bac nhung vao trong DD muoi bac bien oi cung vi s

bien oi cua nong o ion Ag+ trong DD. Do o, bang cach o the cua ien ccnhung vao DD mot muoi a cho cha biet nong o, co the xac nh c hamlng cua ion tng ng trong DD.

Cc da vao the cua no co the suy ra nong o cua ion can xac nh trongDD, goi la cc ch th.

The cua cc ch th c xac nh bang cach so vi the cua mot cc khac goila cc so sanh. Ngi ta dung cac cc nao ma the cua no khong thay oi khi

thay oi nong o ion can xac nh lam cc so sanh. Ngi ta thng dung cchidro tieu chuan lam cc so sanh.

The cua cc hidro tieu chuan c quy c bang khong, do o sc ien ong(Ex) cua nguyen to ganvanic gom cc ch th va cc hidro tieu chuan bang thecua ien cc ch th:

Ex = EInd - ESsKhi ESs = 0 th Ex = EIndTrong thc te, ngi ta thng khong dung cc hidro co the ien cc biet

trc lam cc so sanh ma dung cc calomen.

The cua cc calomen thc te khong thay oi trong thi gian lam viec. Sphu thuoc cua the cc calomen (so vi the cc hidro tieu chuan) vao cac ieukien phan tch c trnh bay trong bang sau:

Khi muon o the cua ien cc (th du cc bac), ta noi no vi cc so sanh(cc calomen, cc hidro, v.v) va mac nguyen to o vao s o e o the(ien the ke, von ke ien t). Trong khi o the, cng o dong c gi unho (t 10-6 en 10-14A). Khi cng o dong nho th nguyen to khong b thayoi.

The cua ien cc la ham so cua hoat o chat. Th du: the cua cc bac trongDD cha ion bac c bieu th bang phng trnh:

E = E0 + 0.059 lg aAg+Bang the cua cc calomen (so vi the cc hidro tieu chuan)The cua cc calomen, V

Nong o DD KCl 200C 250C

Bao hoa 0.2458 0.24901N 0.2819 0.2859

0.1N 0.3369 0.3379

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ay, E0 = 0.7795V the tieu chuan cua qua trnh c bieu th bangphng trnh:

Ag+ + e- AgV vay, hoat o cua ion bac (cung nh hoat o cua cac ion khac) co the c

xac nh bang the E. e cac nh nong o cua ion bac (CAg+), can biet he sohoat o (fAg+):CAg+ = aAg+/ fAg+2. Cach xac nh iem tng ng

Xac nh iem tng ng theo the cua cc ch th: S phu thuoc cuathe cc ch th vao nong o DD co the c dung e xac nh iem tngng khi chuan o. Tai iem tng ng, khi nong o cua ion can xacnh giam i manh va thc te tr thanh khong ang ke th s thay oi otngot the xay ra co the ghi c bang ien the ke nhay.

Th du, neu nhung cc ch th bac va mot cc so sanh vao DD cha ion bac,th cc bac se tch ien dng. Khi chuan o DD cha ion Ag+ bang DDNaCl, nong o ion bac giam i, the cua cc ch th thay oi. The cua cc sosanh khong oi. Do o, trong qua trnh chuan o, cung vi s tng tac cuachat can xac nh (Ag+) vi DD chuan o c them vao (NaCl), ta thayc s bien oi t t va manh dan cua ien the cc ch th. Gan iem tngng, nong o ion bac co s thay oi manh, kem theo bien oi ot ngot thecua cc ch th , o la dau hieu ket thuc chuan o.

S chuan o, trong o iem tng c xac nh bang bc nhay the

cua cc ch th nhung trong DD c goi la chuan o ien the . Chuan oien the c s dung trong cac phng phap trung hoa, oxy hoa kh, kettua va tao phc.ng cong chuan o ien the

Tren hnh 9.1 la ng chuan o ien the ac trng, trong o truc tungat cac gia tr the cua cc ch th, con truc hoanh at cac gia tr the tch DDclorua c them vao.

Hnh 9.1: ng chuan o ien the AgNO3 bang NaCl

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3. ng dungPhng phap chuan o ien the khong nhng ch ng dung rat tot oi vi

s chuan o cac DD co the dung chat ch th ma con ca oi vi viec chuano cac DD co mau, cac DD b uc khi khong the dung c cac phng

phap chat ch th. Chuan o ien the c s dung rong rai e xac nh cacacid, baz yeu va rat yeu, cac hon hp acid hoac baz, cac hon hp chat oxyhoa hoac cac chat kh trong cac moi trng khong phai nc. Cuoi cung,phng phap o the c dung e xac nh pH cua ca DD can nghien cu.Neu truc tung khong ghi cac gia tr the ma ghi cac gia tr , tc la ailng bien thien cua the khi them 1ml DD clorua, th sr4 nhan c ngcong, tren o v tr cua iem tng ng con ro rang hn nhieu (hnh 9.2).

CE /

Hnh 9.2: ng vi phan chuan o ien the AgNO3 bang DD NaClXac nh pH: The cua cc ch th co moi lien he ham so vi nong o cua ionhidro. Cc hidro c chuan b bang cach nhung mot ban platin phu muoiplatin vao DD acid bao hoa kh hidro, tham gia can bang vi ion hidro co:

K = [H+]/[H] hoac K = aH+/aH

Trong o: [H+] nong o ion hidro trong DD[H] nong o kh hidro trong platin khi ap suat khong oi.

EH = E0 +

nF

RTln [H+] hoac EH = E

0 +nF

RTln aH

+

V the cua cc hidro tieu chuan (E0

) bang khong, nen the cua cc hidro cbieu th bang cong thc:

EH =nF

RTln [H+] hoac EH =

nF

RTln aH

+

hoac EH = 0.059 lg [H+] hoac EH = 0.059 lg aH

+

Khi dung cc calomen, the cua no a biet (Ecal), th gia tr Ex cua DD cannghien cu c tnh theo cong thc:

Ex = Ecal - EHhoac - EH = Ex - Ecal

V EH = 0.059 lg [H+

] nen - lg [H+

] = pH = (Ex - Ecal)/0.059 ay Ex: sc ien ong cua nguyen to can nghien cu.

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CHNG 10. PHNG PHAP QUANG PHO HAP THU THAY C1.ac iem cua phng phap phan tch o mau

Trong so nhng phng phap phan tch quang pho th cac phng phap

o mau la nhom c s dung rong rai nhat trong thc tien cua cac phong thnghiem phan tch. Cac phng phap o mau da tren s o cng o cuachum anh sang i qua DD mau.

Phng phap phan tch o mau a c nha bac hoc Nga V. M.Xeverghin phat minh ra t nam 1795.

Trong cac phng phap phan tch o mau, ngi ta s dung cac phanng hoa hoc, trong o chat can xac nh c chuyen thanh mot hp chat comau lam bien oi mau cua DD phan tch. Bang cach o s hap thu anh sangcua DD mau nay (phan tch o mau) hoac bang cach so sanh cng o mau

thu c vi cng o cua DD a biet trc nong o (phng phap so mau),co the xac nh c ham lng cua chat mau trong DD th nghiem.

Moi lien he phu thuoc gia cng o mau cua DD va ham lng cuachat mau trong DD o.S phu thuoc nay c goi la nh luat Buger Lambe Ber no c bieudien bang phng trnh:

I = I0 10- Cl

ay I: cng o chum anh sang i qua DDI0 : cng o chum anh sang ti DD : he so hap thu anh sang, la ai lng khong oi, ac trng chomoi chat mau, phu thuoc vao ban chat cua no;C: nong o chat mau trong DDl: chieu day cua lp DD hap thu anh sang (chieu day cuvet), cmY nghia vat ly cua nh luat nay co the c the

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