C6-Electrolysis

Question 1

What does the word electrolysis mean?

Answer 1

Breaking down using electricity

Question 2

What is the positive electrode called?

Answer 2

The anode

Question 3

What is the negative electrode called?

Answer 3

The cathode

Question 4

What are electrodes often made out of?

Answer 4

An unreactive substance such as graphite or platinum metal.

Question 5

Movement of ions in electrolysis

Answer 5

Positively charged ions move to the cathode
Negative ions move to the anode
This is because opposite charges attract.

Question 6

What is electrolysis used for?

Answer 6

Breaking down an ionic compound

Question 7

Why do ionic compounds not conduct electricity when solid?

Answer 7

Because there ions are in fixed positions in their giant lattice. Ions are held in place by strong electrostatic forces of attraction

Question 8

Why do ionic compounds conduct electricity when molten (melted)?

Answer 8

Because the ions are free to flow within the hot liquid as the forces of attraction are broken

Question 9

What can be done to ionic compounds in order to allow them to conduct electricity if they have high melting points?

Answer 9

Some can be dissolved in water which will allow the ions to become free to move around

Question 10

What do negatively charged ions do to become neutral?

Answer 10

Lose electrons

Question 11

What to positively charged ions do to become neutral?

Answer 11

Gain electrons

Question 12

What ions does water form?

Answer 12

H+ ions - Hydrogen ions
OH- ions - Hydroxide ions

Question 13

If two elements can be produced at an electrode what will form?

Answer 13

The less reactive element will usually be formed

Question 14

Order of discharge at the anode

Answer 14

Halide ion > Hydroxide > all other negatively charged ions

Question 15

Uses of aluminium

Answer 15

Pans
Overhead power cables
Aeroplanes
Cooking foil
Drink cans

Question 16

How can aluminium oxide be obtained?

Answer 16

It comes from the ore Bauxite which can be mined. The impurities such as iron oxide then have to be separated.

Question 17

How can chemists save some energy when melting aluminium oxide?

Answer 17

The aluminium oxide is mixed with molten cryolite which creates a molten mixture which can be electrolysed at 850 degrees.

Question 18

What are the products when brine (concentrated sodium chloride solution) is electrolysed?

Answer 18

Hydrogen gas at the cathode
Chlorine gas at the anode
Sodium hydroxide solution

Question 19

Half equation example: Chlorine loses two electrons

Answer 19

2CL- - 2e- > Cl2

Question 20

In electrolysis how is charge supplied to the electrodes?

Answer 20

Using a power pack

Question 21

Why must the anode be replaced regularly in the electrolysis of Aluminium oxide?

Answer 21

This is because the oxygen molecules produced at the anode react with the graphite (carbon), forming carbon dioxide gas

Question 22

Why is electrolysis very expensive?

Answer 22

Melting the compounds such as aluminium oxide requires a great deal of energy
A lot of energy is required to produce the electric current

Question 23

Why is platinum often used as an electrode?

Answer 23

It is an inert, uncreactive metal

Question 24

Hydroxide ion half equation at anode

Answer 24

40H- - 4e- –> 02 + 2H20

Question 25

How can pure metals be extracted from metal oxides?

Answer 25

Using electrolysis
Adding carbon to reduce the metal (remove oxygen)- This only works when the metal is less reactive than carbon