ANALYSING THE ELECTROLYSIS OF

AQUEOUS SOLUTION

Write half equations for discharge of ions at the anode and the cathode

Predict the product of electrolysis of aqueous solutions

-

+

+

- -

-

- +

+

+

Anions Cations

electrolyte

Anode

ELECTROLYTIC CELL

cathode

Electrochemical Series

Cu+

H+

Pb+

Sn+

Na+

K+

Ca+

Mg+

Al+

Zn+

Fe+

Cl-

Ag+

NO3-

SO42-

F-

Br -

OH-

I-

CATIONS ANIONS

MORE EASY TO DISCHARGE

OH- Cl-

Carbon

H+

H+

OH-

Hydrochloric acid Solution

Cl-

1

Electrolysis of HCl aqueous

Cl-

Step to identify ion in electrolysis of aqueous

solution1. Identify all ion present in aqueous solution

2. Identify ion moving to cathode and anode electrode

3. Identify the ion that will be discharge in cathode and anode

4. Write half equation in cathode and anode

1. Dilute HCl

• H+

• Cl-

• OH-

2. Concentrated HCl

• H+

• Cl-

• OH-

1. Identify all ion present in aqueous solution

1. Diluted HCl

• H+

• Cl-

• OH-

2. Concentrated HCl

• H+

• Cl-

• OH-

cathodecathode

anodeanode

2. Identify ion moving to cathode and anode electrode

1. Diluted HCl• H+

• Cl-

• OH-

2. Concentrated HCl

• H+

• Cl-

• OH-

Choose ion that are lowerIn the electrochemical series for

Diluted HCl and choose ion that are higherIn the electrochemical series

3. Identify the ion that will be discharge in cathode and anode

cathode

anode

cathode

anode

1. Diluted HCl

• H+

• Cathode:

• 2H+ + 2e H2

• OH-

• Anode:

• 4OH- H2O + O2 + e

2. Concentrated HCl• H+

• Cathode:

• 2H+ + 2e H2

• Cl-

• Anode:

• 2Cl- Cl2 + 2e

4. Write half equation in cathode and anode

STEP TO WRITE HALF EQUATION OF DISCHARGE

ION

1. Write reactant and product of reaction

2. Balance the number of atom in both equations

3. Balance the charge of both equation by adding of electron

OBSERVATION EXPERIMENT 6.2

SOLUTION Anode Cathode

DILUTED HCl Gas bubble are released. A colourless gas which relights a glowing

splinter is

produced

Gas bubbles are released. A colourless gas which burns with a pop sound is produced

Concentrated HCl

A greenish-yellow gas with a pungent and choking smell is realesed. The gas turns the blue litmus paper red and then white.

Gas bubles are released. A colourless gas which burns with a pop sound is produced.

The end…………………

OBSERVATION EXPERIMENT 6.3

ELECTRODE

ELECTROLYT

E Anode Cathode

CARBON THE INTENSITY OF THE BLUE COLOUR OF THE ELECTROLYTE DECREASE

Gas bubble are released. A colourless gas which relights a glowing

splinter is

produced

A reddish-brown solid is deposited on the cathode.

COPPER THE INTENSITY OF THE BLUE COLOUR OF THE ELECTROLYTE REMAINS UNCHANGED

Copper electrode dissoves into the solution. The anode become thinner.

The cathode becomes thicker.