Electrolysis

Question 1

Why do covalent compounds not conduct electricity

Answer 1

Because they do not contain charged particles

Question 2

When can ionic compounds conduct electricity and why

Answer 2

When molten or in a aqueous solution as the ions are free to move

Question 3

What does PANIC stand for

Answer 3

Positive
Anode
Negative
Is
Cathode

Question 4

What is a anion

Answer 4

A negative ion

Question 5

What is a cation

Answer 5

A positive ion

Question 6

What is a anode

Answer 6

A positive electrode

Question 7

What is a cathode

Answer 7

A negative electrode

Question 8

What is a electrolyte

Answer 8

A liquid that undergoes a electrolysis

Question 9

Define oxidation

Answer 9

The loss of electrons

Question 10

Define reduction

Answer 10

Gain of electrons

Question 11

What is OIL RIG

Answer 11

Oxygen
Is
Loss of electrons

Reduction
Is
Gain of electrons

Question 12

Define electrolysis

Answer 12

The chemical change caused by passing a electric current through a compound that is molten or in a solution

Question 13

What is the reactivity series

Answer 13

Potassium
Sodium
Calcium
Magnesium
Aluminium
(Carbon)
Zinc
Iron
Lead
(Hydrogen)
Copper
Silver
Gold
Platinum

Question 14

What happened in electrolysis of molten compounds such as lead (II) bromide

Answer 14

Reaction at cathode:
Pb2+ + 2e- —> pb
Réaction at anode:
2Br- — 2e- —> Br2
Or
2Br- —> Br2 + 2e-
Overall equation:
PbBr2 —> Pb + Br2

Question 15

What happens at the cathode in electrolysis of a aqueous solution such as sodium chloride

Answer 15

At the cathode there are two possibilities:
Sodium reduced- Na+ + e- —> Na
Hydrogen reduced- 2H+ + 2e- —> H2
If there is a mixture of ions At the cathode the less reactive element will be the product
Hydrogen is less reactive so when we electrolyte sodium chloride hydrogen is produced

Question 16

What happens at the anode in electrolysis of a aqueous solution such as sodium chloride

Answer 16

At the anode there are two possibilities:
Chloride is oxidised-2Cl- —> Cl2 + 2e- producing chlorine
Hydroxide is oxidised-
4OH- —> O2+2H20 + 4e- producing oxygen
Either the halide is discharged producing a halogen eg chlorine or hydroxide is discharged producing oxygen (and water)

Question 17

What is observed at the anode in the electrolysis of PbBr2

Answer 17

Brown gas (bromine)

Question 18

What is observed at the cathode in the electrolysis of PbBr2

Answer 18

Silvery liquid (lead)

Question 19

What is the direction of electron flow at the cathode and the anode

Answer 19

-away from the anode: the substance is oxidised so loses electrons
-towards the cathode: the substance is reduced so gains electrons

Question 20

What is observed at the anode during the electrolysis of NaCl (aq)

Answer 20

Pale-green gas and bubbles (chlorine)
Test bubbles of gas using damp blue litmus paper which will turn bleached in the presence of chlorine gas

Question 21

What is observed at the cathode during the electrolysis of NaCl (aq)

Answer 21

Bubbles (hydrogen gas)

Question 22

What is observed at the cathode during the electrolysis of CuSO4(aq)

Answer 22

Pink-brown solid (copper)

Question 23

What is observed at the anode during the electrolysis of CuSO4 (aq)

Answer 23

Bubbles (oxygen gas)

Question 24

What happens during electrolysis

Answer 24

Ions are broken down into elements
E.g bromide—> bromine

Question 25

What is the method for core prac 4: electrolysis

Answer 25

1. Assemble the electrolysis circuit by connecting wires to a DC power pack, connecting a crocodile clip to each wire and connecting the GRAPHITE electrodes to the crocodile clips 2. Add approximately 25cm^3 of the first solution to the beaker e.g hydrochloric acid solution 3. Dip the electrodes into the solution 4. Turn the voltage on the power pack to 6V and switch on the electricity 5. Observe the electrolysis and record observations in a results table. With any gas formed test for the presence of chlorine gas using damp blue litmus paper. Test any brown solution formed at the anode with iodine solution for the presence of starch 6. Switch off electricity and clean electrodes with sandpaper then repeat experiment with other solutions

Question 26

What safety may have to be used for electrolysis

Answer 26

-if the solution contains chlorine e.g HCL(aq) do the experiment in a fume cupboard as chlorine gas is toxic -wear safety goggles -do not use a voltage higher than 6V