Electrochemistry

Question 1

Explain with the aid of a labelled diagram how impure copper is purified by electrolysis

Answer 1

Copper sulfate acts as electrolyte with a battery as a power supply
The impure copper is oxidised and is attached to anode
The pure copper acts as a cathode and the copper ions (Cu2+) in solution are reduced

Question 2

Write balanced equations for the reactions that take place at the electrodes for the electrolysis of copper

Answer 2

Cu2+ + 2e¯→ Cu

Cu → Cu2+ + 2e¯

Question 3

What happens to impurities in the copper during electrolysis?

Answer 3

Falls to bottom of container

Question 4

Name a material suitable for use as the electrodes

Answer 4

Platinum

Question 5

How was the current conducted through the electrolyte?

Answer 5

Movement of ions

Question 6

In the electrolysis of aqueous sodium sulfate, what is the ratio for the cathode : anode

Answer 6

cathode : 2

anode : 1

Question 7

In the electrolysis of aqueous sodium sulfate, write the equation at the anode and cathode

Answer 7

Anode - 2H20 -> 2H+ +2é + O2

Cathode - 2H+ +2é -> H2

Question 8

In the electrolysis of aqueous sodium sulfate, when a current passed through the electrolyte for 15 mins, 8.5 cm^3 of gas was collected above positive electrode. What volume of gas was collected above the negative electrode in the same time?

Answer 8

8.5 x 2 =17

Question 9

In the electrolysis of aqueous sodium sulfate, at which electrode did a purple/blue colour appear and why? And at which electrode did a pink colour appear and why?

Answer 9

Purple/blue -> Cathode, OH- ions generated (basic)

Pink -> Anode, H+ ions generated

Question 10

In the electrolysis of potassium iodide, write balanced half equations in both electrodes

Answer 10

Anode - 2I- -> I2 + 2é

Cathode - 2H+ +2é -> H2

Question 11

In the electrolysis of potassium iodide, explain the colour change at the anode and cathode

Answer 11

Anode - Red/brown colour due to Iodine produced

Cathode - Pink due to H+ ions generated

Question 12

In the electrolysis of Acidified water, which species is oxidised?

Answer 12

H20

Question 13

In the electrolysis of acidified water, write the half balanced equations at anode and cathode

Answer 13

Anode - 2H20 -> 2H+ +2é +O2

Cathode - 2H+ +2é -> H2

Question 14

In the electrolysis of acidified water, what is observed?

Answer 14

Bubbles of oxygen and hydrogen being released at the electrodes

Question 15

In the electrolysis of acidified water, what are the products?

Answer 15

Oxygen gas and hydrogen gas

Question 16

Explain with the aid of a labelled diagram the electrolysis of acidified water

Answer 16

acidified h20 [H2SO4] which acts as an electrolyte with a battery as a power supply
The H2O is oxidised and is attached to anode
The H+ ions are reduced at the cathode

Question 17

In the electrolysis of aqueous sodium sulfate, what are the products?

Answer 17

Oxygen gas

Hydrogen gas

Question 18

Explain with the aid of a labelled diagram the electrolysis of sodium sulfate

Answer 18

Dilute Na2SO4 acts as an electrolyte with a battery as a power supply
The H20 is oxidised and is attached to anode
The H+ are reduced at the cathode

Question 19

In the electrolysis of potassium iodide, what are the products?

Answer 19

Iodine

Hydrogen gas

Question 20

In the electrolysis of potassium iodide, what indicator is added?

Answer 20

Phenolphthalein (pink in alkaline conditions)

Question 21

In the electrolysis of sodium sulfate, what indicator is added?

Answer 21

Universal indicator

Question 22

Explain with the aid of a labelled diagram the electrolysis of potassium iodide

Answer 22

Dilute Pottasium iodide acts as an electrolyte with a battery as a power supply
The I- ion is oxidised and is attached to anode
The H+ ion are reduced at the cathode

Question 23

In the electrolysis of potassium iodide, what is the role of K+ ions

Answer 23

They are spectator ions as they are too stable to be discharged

Question 24

For the electrolysis of copper sulfate, what are the products?

Answer 24

Purified copper

Question 25

What occurs/is observed in the anode when the Cu is oxidised

Answer 25

The anode disintegrates

The copper is being converted into ions and dissolving into the solution

Question 26

What occurs/is observed when Cu2+ is reduced?

Answer 26

Cathode builds up with pure copper deposited

The copper ions from solution are being converted into copper atoms depositing into anode

Question 27

What is electrolysis?

Answer 27

Breaking up of a substance due to the passage of an electric current though it in an aqueous solution or when molten (coined by Faraday)

Question 28

What is an electrolyte?

Answer 28

Substance that causes electricity as it has ions that can move

Question 29

What are inert electrodes?

Answer 29

Electrodes do not react with the electrolyte

Question 30

What are active electrodes?

Answer 30

Electrodes that do react with the electrolyte they are in

Question 31

Where does oxidation occur

Answer 31

Anode

Question 32

Where does reduction occur?

Answer 32

Cathode

Question 33

What is electroplating and give examples

Answer 33

Process where electrolysis is used to put a layer of one metal on the surface of another metal
Gold plating [jewellery], EPNS nickel cutlery can be pated with silver [cutlery]