capter 6 4 utarid

8/6/2019 capter 6 4 utarid

1/20


2/20


3/20

Electrolyte

an electrolyte is a chemical compound which conduct

electric current in a molten state or an aqueous solution

and undergoes chemical change.

electrolyte contain ions which move about freely to

carry electrical charges.

An electrolyte can break down into elements at

electrodes when an electric current flow through it.


4/20

Non- electrolyte

a non-electrolyte is a chemical compund which cannot

conduct electrical current

all states.

there will be no change on a non-electrolyte when an

electric current flow through

it.

non- electrolyte are made from molecules only. There are

no ions which can carry electrical charges in non-

electrolytes.


5/20

Electrolysis of Molten

CompoundsElectrolysis process

electrolysis is the process of breaking down chemical compounds

into their constituent element using electrical current.

Example:

Molten aluminium electric current aluminium + oxygen

oxide

Copper(II) chloride electric current copper + chlorineSolution


6/20


7/20


8/20

Electrolysis of moltencompounds1) During electrolysis, anions (negative ions) will be pulled

towards the anode (positive electrode). At the anode, anions

will be discharged by releasing electrons to the anode.

2) Cations (positive ions) will be attracted towards the cathode

(negative electrode). at the cathode, cation will be

discharged by accepting electrons from the cathode.


9/20

Predicting products of electrolysis

of molten compounds

Example

Electrolysis of molten zinc iodide, using carbon

electrodes

Solution

Molten zinc iodide, containing and ions.

Anode:

Half equation:

Observation: Purple vapour is released

Product: : Iodine, gas

Cathode:

Half equation:

Observation: grey metal is formed

Product: zinc, Zn metal


10/20

+ -

-- - - - - - -- -

-- --

-- -- --

-- -- - -

Anode Cathode

Iodide ions are selected todischarged

I- Zn+

Electrolysis ofMolten Zinc Iodide

Carbonelectrode


11/20

6.2.1 Electrolysis of Molten Compounds

(i) Moltenlead (II) bromide

Objective:

To investigate the electrolysis of molten lead (II) bromide,

PbBr2

Apparatus: A 6-volt battery, two carbon, C electrodes, four wires with

crocodile clips, a switch, an ammeter, a rheostat, a crucible, a

tripod stand with pipe clay triangle, a Bunsen burner, and

matches.

Materials:

Lead (II) bromide, PbBr2


12/20

CAUTION!

Carry out this activity in a well-ventilated place as bromine

vapour, Br2, is poisonous and pungent.

Procedure:

1 A crucible is filled with solid PbBr2until it is half full.

2 The solid lead (II) bromide is heateduntil it is completely melted.

3 The apparatus as shown in Figure 6.3

is set up.

4 The switch is turned on to allow the

electricity to pass through the molten

lead (II) bromide for about 20 minutes.

5 After that, the switch is turned off and both electrodes are taken

out from the electrolyte. The molten lead (II) bromide is carefully

poured into a beaker using tongs.6 The observation at the anode and cathode are recorded.

Switch


13/20

Substance Does the bulb

lightup?

Observations Conclusion

At anode: A reddish-

brown gas is given off

At cathode: A gray

substance is deposited

Molten lead(II) bromide,

PbBr2

Yes Molten lead(II) bromide,

PbBr2 conducts

electricity. Bromine, Br2

gas is given off at the

anode. Lead, Pb is

deposited at the cathode.

Solid lead(II) bromide,

PbBr2

No No change at electrodes Solid lead(II) bromide,

PbBr2 does not conduct

electricity.

Observation:


14/20

Observation:

Electrode Observation

Anode

Cathode

A brownga

s with

pungent

and c

h

oking smellis released.

A shiny-silver globule is formed atthe bottomof the crucible.

The ammeter shows a reading.

Discussion:1. The molten lead (II) bromide contains .

and that move freely.

lead (II) ions, Pb2+

bromide ions, Br

2. The lead (II) ions move to the while the

bromide ions move to .

cathodeanode

3. At the cathode: Each lead (II) ion is discharged by

electrons to form a lead atom, Pb.

Half equation:

acceptingtwo

Pb2+(l) Pb(s)

+2 0

+ 2e

CD3_50.C2


15/20

Discussion:1. The molten lead (II) bromide contains .

and that move freely.

lead (II) ions, Pb2+

bromide ions, Br

2. The lead (II) ions move to the while the

bromide ions move to .

cathodeanode

3. At the cathode: Each lead (II) ion is discharged by

electrons to form a lead atom, Pb.

Half equation:

acceptingtwo

Pb2+(l) Pb(s)

+2 0

+ 2e

4. At the anode: Each bromide ion is discharged by

electron to form a bromine atom, Br.donating one

Br(l) Br(l)

-1 0

+

e

Half equation:

Br(l) Br2(g)+ Br(l)

2Br(l) Br2(g) + 2e


16/20

Half equation: Pb2+(l) Pb(s)+ 2e

Half equation: 2Br(l) Br2(g) + 2e

Overall equation: 2Br(l) Br2(g) + Pb(s)+ Pb2+(l)

The electrolysis of molten lead (II) bromide producesatthe cathode andatthe anode.

Conclusion:

lead metal

bromine gas


17/20

Exercises: Below are compound in molten state.

Name of

compound

Ions produced Ions that move to

Anode Cathode

Zinc chloride

Magnesiumoxide

Calcium oxide

Aluminium

iodide

Zn2+ & Cl- Cl- Zn2+

Mg2+ & O2- O2- Mg2+

Ca2+ & O2- O2- Ca2+

Al3+ & I- I- Al3+


18/20

Name of

compound

Half equation Products formed at

Anode Cathode Anode Cathode

Zinc chloride

Magnesium

oxide

Calcium

oxide

Aluminium

iodide

Exercises

Cl- Zn2+

O2- Mg2+

O2- Ca2+

I- Al3+

Cl2 Zn

O2 Mg

O2 Ca

I2 Al

Cl- Cl2 + 2e2

-2 0

Zn2+ Zn+ 2e

+2 0

O2- O2 + 2e2 Mg2+ Mg+ 2e

O2- O2 + 2e2 Ca2+ Ca+ 2e

I- I2 + 2e2 Al3+ Al+ 3e


19/20

6.2: Electrolysis of Molten Compounds6.2: Electrolysis of Molten Compounds

1. Identify cation & anion present in compound

2.Identify anion attracted to anode

3. Determine number of electrons involved in discharge (the number of

electrons is equal to the charge on the ion

Product of electrolysis is at the right hand side of chemical equation

Predicting the products of electrolysisPredicting the products of electrolysis

4. Write half-equation of cation

gaining electrons

4. Write half-equation of anion

losing electrons

5. Write balance chemical equation by adding the two half-equations

2.Identify cation attracted to cathode


20/20

+ -Anode Cathode

Carbonelectrode

- -

--

- Molten sodium chloride

compound

1- why does sodium chloride need to be in molten form?

2-name particles in molten sodium chloride.

3- name the ion attracted to the anode and the cathode.4- what can be observed at the anode and the cathode?

5- what are the products formed at the anode and the cathode?

6- write the half equation for the equation occuring at the anode and the

cathode.

Test yourself!

Documents

capter 6 4 utarid