Electrolysis

Question 1

What is an electrolyte?

Answer 1

(Ionic) liquids and solutions are able to conduct electricity

Question 2

What is electrolysis?

Answer 2

the use of electrical current to break down compounds containing ions into their constituent elements

Question 3

What happens during electrolysis?

Answer 3

Positively charged ions move to the negative electrode (the cathode),

negatively charged ions move to the positive electrode (the anode).

Ions are discharged at the electrodes producing elements.

Question 4

which electrode are metals produced at?

Answer 4

cathode

Question 5

which electrode are non-metals produced at?

Answer 5

anode

Question 6

Why is electrolysis an expensive process?

Answer 6

because it requires lots of heat and electrical energy

Question 7

Metals can be extracted from ________ using electrolysis

Answer 7

molten compounds

Question 8

When is electrolysis used to extract metals?

Answer 8

if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon.

Question 9

Why are large amounts of energy needed for electrolysis

Answer 9

to melt the compounds and to produce the electrical current

Question 10

How is Aluminium oxide’s melting point reduced?

Answer 10

cryolite is mixed with aluminium oxide

Question 11

Why is does Aluminium oxide melting point need to be reduced?

Answer 11

because high melting point means that a lot of energy would need to be produced in order to melt aluminium oxide which is expensive

Question 12

the positive aluminium ions (A3+) will form at which electrode?

Answer 12

the cathode

• it will then sink to the bottom of the electrolysis tank

Question 13

the oxygen ions of aluminium oxide will form at which electrode

Answer 13

the anode

Question 14

Why does the anode in aluminium oxide electrolysis need to be replaced regularly?

Answer 14

because oxygen will react with the carbon which will wear the anode away

Question 15

What happens at the cathode in electrolysis of aqueous solutions?

Answer 15

• hydrogen is produced if the metal is more reactive than hydrogen
• A solid layer of the pure metal will be produced if the metal is less reactive than hydrogen

Question 16

What happens at the anode in electrolysis of aqueous solutions?

Answer 16

• oxygen is produced

However…….

if halide ions are present the halogen is produced

Question 17

Why is direct current used in electrolysis

Answer 17

The power supply must be direct current (dc) so that the current passes in one direction only. The power supply is acting as an electron pump. The electrons flow through the external circuit and enter the electrolytic cell via the cathode, which gains a negative charge and so is the negative electrode. Electrons leave the electrolytic cell via the anode, which then has a positive charge and so is the positive electrode.

But if we pass an ac current the polarity of the electrodes will be continuously changing and the ions will not be attracted towards any particular electrode resulting in no ionization.

Question 18

What is electroplating?

Answer 18

uses electrolysis to coat a cheap metal with a more expensive one (for example, silver) or for protection (for example, chrome plating for car parts).

The object to be electroplated is always made the negative electrode in order to attract the positive silver ions. The positive electrode should be made of the pure metal that is to be plated, in this case silver. The electrolyte should also contain the metal ions to be plated on to the jug.

Question 19

How is copper purified using electrolysis ?

Answer 19

Electrolytic refining is used to purify copper. A small piece of pure copper is chosen as the cathode. The anode and the electrolyte supply the copper ions for the electrolysis.

At the anode, copper atoms lose electrons (are oxidised) to form copper(II) ions. The half-equation for the anode reaction is:

Cu(s) → Cu2+(aq) + 2e−

These oxidised copper ions move through the solution to the cathode

At the cathode, copper(II) ions gain electrons (are reduced) to form copper atoms which are plated on to the pure copper electrode. The half-equation for the cathode reaction is:

Cu2+(aq) + 2e− → Cu(s)

Anode sludge (bunch of impure metals) form at the bottom