Topic 8 - Electrolysis

Question 1

Cation

Answer 1

Positive ion

Question 2

Anion

Answer 2

Negative ion

Question 3

Electrolysis

Answer 3

The breaking down of a compound using electricity.

Question 4

Electrolyte

Answer 4

Ionic compound that is molten or dissolved in water.

When an ionic substance is melted or dissolved in water this allows the ionic bonds to break. This allows the ions to move freely when a voltage is applied. An ionic compound with free moving ions is called an electrolyte.

Question 5

What happens during electrolysis?

Answer 5

Electrical energy is transferred to decompose the electrolyte. The ionic compound is broken down into positive cations and negative anions.

Question 6

Electrode

Answer 6

Positive and negative ‘rods’

Question 7

Anode

Answer 7

Positive electrode

Question 8

Cathode

Answer 8

Negative electrode

Question 9

Are metal ions positive or negative?

Answer 9

Positive

Question 10

Are non-metal ions positive or negative?

Answer 10

Negative

Question 11

What happens to cations?

Answer 11

They are attracted to the negative cathode where they gain electrons to become atoms (reduction)

Question 12

What happens to anions?

Answer 12

They are attracted to the positive anode where they loose electrons to become atoms (oxidation).

Question 13

What does an ion turn into when it goes to an electrode?

Answer 13

Atoms

Question 14

What atoms do lead bromide turn into?

Answer 14

Lead + bromine
The negative bromide ions are attracted to the positive anode and turn into bromine atoms.
The positive lead ions are attracted to the negative cathode and turn into lead atoms.

Question 15

What column on the periodic table requires a 2 in the equation?

Answer 15

Hydrogens
2nd column to the end.

Question 16

What does molten mean?

Answer 16

Melted
Not with water

Question 17

What is a solution?

Answer 17

Dissolved
With water

Question 18

What is produced when a solution is used in electrolysis?

Answer 18

Water
H2O —> H+ + OH-
Hydrogen + Hydroxide

Question 19

Where does H+ go to?

Answer 19

Cathode

Question 20

Where does OH- go to?

Answer 20

Anode

Question 21

What are the rules for producing products in electrolysis at the cathode?

Answer 21

If the metal is less reactive than hydrogen it is made at the cathode.
If the metal is more reactive than hydrogen, hydrogen will be made at the cathode.

Question 22

What are the rules for producing products in electrolysis at the anode?

Answer 22

If the anion is chloride, bromide or iodide then the halogen will be made.
If the anion is sulphate, nitrate or carbonate then oxygen will be made.

Question 23

Half equation for oxygen

Answer 23

4OH- —> 2H2O + O2 + 4e-

Question 24

Half equation for hydrogen

Answer 24

2H+ + 2e- —> H2

Question 25

Method for the process of electrolysis of copper sulfate solution using copper electrodes?

Answer 25

1) 50.0 cm3 copper sulphate solution. 2) Wash and clean copper electrodes with emery paper. 3) Record mass of copper electrodes. 4) Change variable resistor until ammeter read 0.2A 5) Power pack 4v for 5 minutes 6) Record number of amps 7) Rinse each electrode with propane, dry and record mass. 8) Repeat steps 2 to 7 for different amps.

Question 26

Results of practical at the cathode?

Answer 26

The higher the current the larger the change in mass of electrodes in 20 minutes. The cathode gets heavier as copper ions gain electrons (reduced) and form pure copper metal which is deposited on the cathode. When the current is higher the electrons are provided more quickly.

Question 27

Results of practical at the anode?

Answer 27

The anode gets lighter as the copper atoms loose electrons (oxidised) and form copper ions which dissolve into the solution. When the current is higher the electrons are removed more quickly.

Question 28

Product and half equation at the anode?

Answer 28

Cu —> Cu2+ + 2e-

Question 29

Product and half equation at the cathode?

Answer 29

Copper Cu2+ + 2e- —> Cu

Question 30

Why should you clean electrons at start with emery paper?

Answer 30

To remove impurities.

Question 31

What is an ammeter used for?

Answer 31

To measure the voltage of the solution.

Question 32

Why is a variable resistor used?

Answer 32

To change the current.

Question 33

Why should you measure the time of electrolysis?

Answer 33

So you can compare how much mass is added or lost in the same amount of time.

Question 34

What do you use to wash and dry electrodes and why?

Answer 34

Acetone because it evaporates.

Question 35

Why should you dry the electrodes at the end?

Answer 35

The electrolyte will still be on it and it has a big mass so can affect the results.

Question 36

Which electrode is pure?

Answer 36

Cathode

Question 37

Which electrode is impure?

Answer 37

Anode

Question 38

Oxidation

Answer 38

Loss of electrons

Question 39

Reduction

Answer 39

Gain of electrons.

Question 40

Method for electrolysis of copper sulfate solution using inert electrodes?

Answer 40

1) 50cm3 of copper sulphate solution 2) Graphite electrodes 3) Power pack 4v for 5 minutes 4) Observe positive electrode 5) Observe negative electrode

Question 41

Results at positive anode for electrolysis of copper sulfate solution using inert electrodes?

Answer 41

Bubbles Oxygen made 4PH- —> O2 + 2 H2O + 4e-

Question 42

Results at negative cathode for electrolysis of copper sulfate solution using inert electrodes?

Answer 42

Orange solid Copper Cu2+ + 2e- —> Cu