Chemisty || Electrolysis C9

Question 1

What Is Electrolysis?

Answer 1

The breaking down of a substance using electricity,

An electric current is passed through a electrolyte, causing it to decompose,

Reduction and oxidation both occur.

Question 2

Electrolyte?

Answer 2

A molten or dissolved ionic compound.

Question 3

Oxidation In Terms Of Electrolysis?

Answer 3

Loss of electrons.

Question 4

Reduction In Terms Of Electrolysis?

Answer 4

Gain of electrons.

Question 5

Cations?

Answer 5

Positive ions,

Move towards the negative electrode,

They are reduced (gain electrons).

Question 6

Anions?

Answer 6

Negative ions,

Move towards the cathode,

Are oxidised (loose electrons).

Question 7

Cathode?

Answer 7

Negative electrode.

Question 8

Anode?

Answer 8

Positive electrode.

Question 9

What Happens When Ions Discharge?

Answer 9

They gain or lose electrons,

This forms a uncharged substance and they are then discharged from the electrolyte.

Question 10

Half Equations?

Answer 10

Show how electrons are transferred during reactions,

They show what happens at each electrode during electrolysis,

E.g. Na —> Na+ + e-
This shows Sodium loosing one electron to become a sodium ion,

The charges should balance on each side of the equation.

Question 11

Electrochemical Cell?

Answer 11

A circuit that is made up of an - anode, 
cathode, 
electrolyte, 
power source,
Wires that connect the two electrodes.

Question 12

Setting Up A Electrochemical Cell When You Have A Solution?

Answer 12

Get two inert electrodes,

Clean the surface of the electrodes using some emery paper (or sandpaper),

Do not touch the electrodes with your hands from now as this can transfer grease to them,

Place both electrodes into beaker filled with your electrolyte,

Connect the electrodes to a power supply using crocodile clips and wires,

When the power supply turns on, the current will flow through the cell.

Question 13

Inert?

Answer 13

Means “unreactive”,

Electrodes can be unreactive,

E.g. graphite or platinum.

Question 14

Setting Up A Electrochemical Cell When You Have A Molten Ionic Substance?

Answer 14

Put your solid ionic substance in a crucible,

Heat the crucible with an Bunsen burner until the solid becomes molten. This should be done in a fume cupboard to avoid toxic fumes going into the room,

Once the solid has molten, dip two clean, inert electrodes into the electrolyte,

Connect the electrodes to a power supply using wires and crocodile clips,

A current should flow through the cell when the power is turned on.

Question 15

How To Test A Electrochemical Cell?

Answer 15

You could put a ammeter or bulb in the series to check if it is working.

Question 16

Why Can A Solid Not Be Electrolysed?

Answer 16

Because the ions are fixed in positions and cannot move.

Question 17

Why Can Molten Ionic Compounds Be Electrolysed?

Answer 17

Because the ions can move freely and conduct electricity.

Question 18

Metals Are?

Answer 18

Positive and go to the cathode.

Question 19

How To Predict The Electrolysis Of A Molten Substance?

Answer 19

The substances are ionic compounds so one is a metal and one is a non metal,

The metal is positive so it will go to the cathode,

The non metal is negative and will go to the anode.

Question 20

What Cab Be Produced At The Anode?

Answer 20

Molecules or atoms.

Question 21

What Cab Be Produced At The Cathode?

Answer 21

Atoms.

Question 22

In Aqueous Solutions, What Else Will Be Present In The Electrolyte?

Answer 22

Hydrogen ions (H+) and hydroxide ions (OH-),

They come from the water.

Question 23

In Aqueous Solutions, What Happens At The Cathode?

Answer 23

H+ ions will come from the water,

Metal ions will also be present from the ionic compound,

They both travel to the cathode,

Hydrogen gas is produced at the cathode when the metal is MORE REACTIVE than hydrogen (e.g. copper or silver),

Pure metal is produced at the cathode when the metal is LESS REACTIVE than hydrogen.

Question 24

In Aqueous Solutions, What Happens At The Anode?

Answer 24

OH- ions from the water and halide ions from the ionic compound both go to the anode,

If halide ions are present (e.g. Cl-, Br- and I-), then molecules of that substance will be formed. E.g. if halide ions Cl- goes to anode, Chlorine ions will form,

If no halide ions are present, then oxygen will form.

Question 25

How To Tell If A Gas Is Being Produces Af An Electrode?

Answer 25

Bubbles will form.

Question 26

Practical - Electrolysis Of Copper Sulphate?

Answer 26

Copper Sulphate contains four different ions,

Place Copper Sulphate in electrochemical Cell with inert electrodes,

At the cathode, copper and hydrogen will be present. Copper is less reactive than hydrogen so copper metal is produced at the cathode. A coating of copper can be seen,

There are no halide ions present so oxygen and water are produced at the anode.

Question 27

Copper Sulphate Formula?

Answer 27

CuSO4.

Question 28

Four Different Ions In Copper Sulphate?

Answer 28

Cu2+,

SO42-,

H+,

OH-.

Question 29

Practical - Non-Inert Electrodes?

Answer 29

Set up electrochemical cell using copper electrodes,

Place the copper sulphate in beaker, the same as the other practical,

Make sure the electrodes are dry and weigh both the anode and cathode,

Find the difference between the masses of anode and cathode again,

Leave the practical for 30 minutes,

As the reaction happens, the mass of the cathode will increase and mass of anode will decrease. This is because copper transfers from the anode to the cathode,

Find the difference between the masses of anode and cathode again. This difference should be a lot more,

Increase the current (e.g. by adding batteries). This will increase the rate of electrolysis and there will be a bigger difference between the two electrodes.

Question 30

Electrolysis Of Copper Sulphate With Inert Electrodes Half Equations?

Answer 30

Cu2+ + 2e- —> Cu
Cathode ^,

4OH —> O2 + 2H2O + 4e-,
Anode ^.

Question 31

How Is Copper Extracted Using Electrolysis?

Answer 31

Done this way, the copper is purified,

Before the electrolysis, the anode starts as a big lump of impure copper,

The electrolyte is Copper Sulphate Solution (contains Cu2+ ions),

The cathode is a this piece of pure copper,

During the process:
- The impure Copper anode is oxidised, dissolving into the electrolyte (Copper Sulphate Solution) to form copper ions,

• The copper ions are reduced at the pure copper cathode and add to it as a layer of pure copper,

Any impurities from the impure copper anode sink to the bottom of the electrochemical cell, this forms a sludge.

Question 32

A Sludge?

Answer 32

The impurities that release off the impure electrode,

They sink to the bottom and form a sludge.