Phng php phn tch tt sau khi phi kh, p nh ri ray qua ray 2 mm.
Phn c kch thc ln hn 2 mm c cn khi lng ri i (khng th phn tch thnh
phn ca t). Lng t c nghin nh bng chy v ci nghin ln ri ray qua ray 1
mm sau cho vo cc bch chun b sn c ghi tn gin nhn. 1. pH ( chua ca t)
( pH H2O) 1.1 Nguyn l v l thuyt chung pH = - lg aH, l i lng biu th
hot ng H+ trong mi trng t. y l ch tiu n gin u tin v chua thng c xc
nh nht, n c ngha rt ln trong vic nh gi tnh cht ca t. a s t Vit Nam
l t chua . pH phn nh mc ra tri cc cation kim v kim th cng nh mc tch
t cc cation st, nhm trong t. - C 3 loi pH thng xc nh: pH nc l pH o
tc ng ca t v nc. pH mui trung tnh l pH o tc ng t v mui trung tnh.
Vd pH KCl pH NaF l pH o tc ng ca t vi NaF 1 M l mt loi mui thu phn
c mi trng kim. i vi t chua pH nc > pHKCl v tc ng NaF do phn ng
to phc ca Al 3+ vi F to thnh OH do lm tng mnh pH. Mc tng pH khi tc
ng vi NaF so vi pHKCl phn nh mc c mt ca Al3+. Php o thng dng v tiu
chun hin nay l php o in th, s dng pH met in cc thu tinh. 1.2 Thit b
pH mt in cc thu tinh My lc ng h bm giy. 1.3. Thuc th Cc dung dch m
pH tiu chun : 4.01; 6.86; 9.18. Cc dung dch trao i : KCl 1 M . Nc
ct c dn in ring khng ln hn 0.2 ms/m v pH = 5.6-6.6 250C. 1.4 Thc
hnh Xc nh pH nc v pHKCl1
- Cn 10g t mn kh khng kh cho vo vo trong bnh nha dung tch 100ml
ming rng. - Thm 50ml H2O ct ( hoc KCl nu o pH KCl) Lc bng tay cho
phn tn t v tip tc lc bng my 30 pht (vn tc maximum) sau yn trong
khong 2 gi (khng qu 3 gi). Lc xoy li 2-3 ln bng tay cho phn tn huyn
ph. o pH bng pH mt in cc thy tinh. V tr bu in cc v tr trung tm v
trung im su ca dung dch trong huyn ph. c kt qu o sau khi kim ch n
nh 30 giy (mu c o 2 ln lp li).
Theo s liu kt qu th nghim pH ca t l: 5.5-6 Gn trung tnh >6
Trung tnh
pH < 4.5 4.5-5 5-5.5 Xp loi Rt chua Chua va Chua nh 2. Xc nh
tnh thm nc ca t (CMR) mu. S sai s gia cc phng php khng ln.
C nhiu phng php khc nhau ty theo di mi phng th nghim v c th ty
theo s lng Chun b dng c bao gm:
Cn ton b dng c, ghi li kt qu cn ln 1. Cn 50 g t, cho vo pha trn
tm giy lc. Thm H2O vo ngp t, y tm giy lc.
D lng hn 2 h hoc qua m (giai on ny kim tra mc hp thu nc cao nht
ca t). M u kp nc thot xung erlen. yn khong 30 pht rt nc hon ton v
lm kh b mt giy thm. Sau cn li khi lng ca ton b h thng. Da vo cng
thc tnh ra %. Tnh thm nc ca t l: 3. Dung lng cation trao i
(CEC)
3.1 Nguyn l v l thuyt chung Dung lng cation trao i (CEC) l dung
lng hp th cation ca phc h keo t. Lng v cht ca CEC l mt ch tiu quan
trng v ph nhiu ca t phn nh kh nng cha ng v iu ho dinh dng c lin
quan n phng php bn phn hp l. Cc bc tin hnh nh sau: - Bo ho t bng mt
cation, cation ny phi thay th ht cc cation t hp thu v cha y kh nng
hp thu ca t ( hay gi l cation bo ho). - Ra sch ht nhng cation ngoi
tng hp thu ca t.2
- y ton b cation bo ho ra bng mt cation khc. - Xc nh s meq ca
cation bo ho c y ra v t suy ra CEC ca t bng s me/100 g t ( hoc
Cmol/kg t) Cc lu m bo kt qu chnh xc cn phi ch mt s c im sau: - m bo
chit lin tc, ng tc qui nh. - Khng c kh mt mu, khng c gin on gia cc
bc (c th: sau khi bo ho cation lp tc phi ra, sau khu ra lp tc phi y
cation bo ho). - Khng c lt mu, kh mu. Cn ng nht cc yu t vi tt c cc
mu. K thut chung ca 3 bc CEC l ra, trao i v thay th cation bo ho l
nh nhau ch cn thc hin c 3 yu cu nu l m bo kt qu tt. Nhng cn phi bit
vi tng loi t khc nhau kh nng hp thu v trao i khc nhau nn t l t:
dung dch v thi gian trao i c th khc nhau. 3.2 Phng php amon acetate
Nguyn l: amon acetate l phng php s dng dung dch amon acetate 1M (pH
= 7) l dung dch bo ho cation. Cation NH4+ s y ht cc cation trong
tng cation hp thu ca t v lm no cation ton b kh nng hp th ca t. Xc
nh NH4+ - CEC bng phng php Kjendhal. u im ca phng php - C m 2 chiu
cao, pH ca dch hu nh khng thay i trong qu trh trao i cation v pha
long. - Ion bo ho NH4+ l ion biu kin c xc nh d dng v chnh xc bng
phng php Kjendhal. Mc d vy phng php cng c nhng nhc im nh: - i vi t
c cht hu c cao, nhng t c cha kaolin ng k, halloysit hoc nhng khong
st dng 1:1 khc th chit rt bng amon axetat u a n kt qu thp hn ca dch
bari axetat hoc bari clorua- trietanolamin. - Nhng loi t c cha
vecmiculit th cc cation Ca2+, Mg2+, Na+ hay H+ khng th y ra. - t
canxit cng cho kt qu thp do mt t CaCO3 ho tan s cung cp mt lng Ca2+
ng bo ho amon.
3
Ngoi ra s dng NH4+ lm cation bo ho v l cation biu th th vic ra
bng nc l khng th c do NH4+ b thu phn to thnh NH4OH ho tan lm gim
CEC. Do cn ra bng etanol 95% hoc 80 %( Nu nng thp NH4+ khng ra ht v
lm tng CEC). 3.3 Thit b- dng c Semi micro Kjendhal v cc thit b o th
tch tng ng. Bnh 250 ml Phu thu tinh Ct acid Bng thu tinh Giy lc 3.4
Ho cht Amon axetat NH4CH3COOH (pH=7): Cn 77.08 g NH4CH3COOH pha 400
ml nc ri thm gn 1 lt. Kim tra pH v thm NH4OH cho ng pH=7.0 ri nh n
1 lt. Etanol 80%: 800 ml etanol pha vi 200 ml nc ct. KCl hay NaCl
10%: ho tan 100 g KCl (hay NaCl) vo khong 1 lt nc ct. 3.5 Thc hin
th nghim thc hin phn ny nn lm vo bui sng c thi gian lc. Mu thc hin
2 ln lp li cng vi 1 mu i chng . - Cn 3 g ct x l ( H2SO4, nung , ra
sch), dng tay lc nh to thnh lp mn trn b mt. - Cn 7g + 3 g t trn u
thnh 1 dy ng nht, tht nh to thnh 1 lp th 2 ph trn b mt lp th nht .
- Cn tip 3 g ct x l, tri u tht nh, to thnh 1 lp ph th 3. Ct 1 mu
giy lc nh, va vi ng knh ca phu, t ln trn b mt nhm gim p lc nc v
dung dch cho vo. Dung dch cho vo: - 50 ml cn 80%, lng. - 200ml dung
dch NH4CH3COOH (pH=7), lng. - 100 ml cn 80%, lng. Ch : Cc dung dch
cho vo lin tip trnh cho b mt giy thm b kh. Ch dung dch th 3 lc qua
thay th bng 1 bnh nha V= 150-200 ml mi. - Thm nh nhng 100ml KCl (
pH
