C3.4 - Electrolysis

Question 1

What is Electrolysis?

Answer 1

Decomposition of an ionic compound using electricity

Question 2

What is an electrolyte?

Answer 2

A compound in its liquid state / a solution that has mobile ions / is able to conduct electricity.

Question 3

What is an Electrode?

Answer 3

An anode / cathode - made from metals/graphite and are able to conduct electricity to the electrolyte

Question 4

Cathode detention?

Answer 4

Negative electrode

Question 5

Anode detention?

Answer 5

Positive electrode

Question 6

What are the two rules for electrolysis of solutions?

Answer 6

• If the ions of a metal are more reactive than hydrogen, hydrogen will be produced at the cathode
• Oxygen is produced at anode, if there are no ions of group 7 present. If they are then the group 7 element is produced instead

Question 7

What is less reactive than hydrogen ?

Answer 7

Copper, silver, gold, platinum

Question 8

Group 7 elements ?

Answer 8

Fluorine, iodine, chlorine, bromine, astatine

Question 9

Why are the electrodes made up of graphite?

Answer 9

• graphite is a conductor
• graphite is inert

Question 10

What ions are attracted to what electeodes?

Answer 10

• Positively charged ions are attracted to the negative electrode ( cathode )
• Negatively charged ions are attracted to the positive electrode (anode )

Question 11

Why is electrolysis important?

Answer 11

It enables us to isolate different elements and extract useful elements

Question 12

What happens at the cathode?

Answer 12

Reduction - the ions gain electrons to form a full outer shell

Question 13

What happens at the anode?

Answer 13

Oxidation - the ions lose electrons

Question 14

Draw a diagram of electrolysis?

Answer 14

Yes :

Question 15

Why is copper purified using electrolysis?

Answer 15

Since mining is a labour intensive and expensive alternative

Question 16

What ions are involved in the electrolysis of a solution?

Answer 16

The ions of the compound, OH-, H+

Question 17

For example : Explain how sodium bromide solution is separated?

Answer 17

Because it is a solution there ar H+ Ions a OH- ions present, as well as K+ and Br- ions. At the anode, which is positive, negative anions ( Br- and OH- )are attracted but since Br- is a halide ion it is discharged and OH- reminds in the solution. 2Br —> Br2 + 2e-. At the cathode which is negative, positive cations ( H+ and K+ ) are attracted but only hydrogen is discharged since potassium is more reactive than hydrogen so it remains in the solution 2H+ + 2e- —> H2 therefore hydrogen gas has formed.

Question 18

What is the difference in electrolysis between molten and aqueous substances?

Answer 18

Molten substance don’t contains OH- or H+ ions whilst aqueous do

Question 19

What is electroplating?

Answer 19

Electroplating uses electrolysis to put a thin layer of a metal onto a metal object

Question 20

How is electrolysis used to purify copper?

Answer 20

You need a pure and impure copper rod for the anode and cathode as well as copper sulphate solution.
- at the anode, copper atoms lose electrons to form copper ions, which dissolved in a solution ( oxidation )Cu —> Cu2+ + 2e-
- At the cathode copper ion from the solution and impure, copper gain electrons to form a pure copper ( reduction ) Cu2+ + 2e- —> Cu

Question 21

Why is the sludge as a result of copper purification kept and not thrown away?

Answer 21

Factories keep this instead of throwing it out since it may contain rare metals

Question 22

Why do people/ factories electroplate objects/ products ?

Answer 22

• To protect them from harm, to protect them from reacting with the surroundings
• To make them look pretty/ give them an appealing look
• A cheap alternative to making the whole thing in that particular shiny metal/ or just metal in general