Chemistry 5.4

Question 1

What is electrolysis?

Answer 1

The breaking down of a compound using electricity.

Question 2

What is the positive electrode called?

Answer 2

Anode

Question 3

What is the negative electrode called?

Answer 3

Cathode

Question 4

Mnemonic to remember which electrode is which?

Answer 4

Positive
Anode
Negative
Is
Cathode

Question 5

What must electrodes be made out of and why?

Answer 5

Graphite or platinum
Must be made from a solid that conducts electricity but is inert.

Question 6

If the question mentions that a solution or dilute substance is being used, which type of electrolysis is used?

Answer 6

Aqueous electrolysis

Question 7

What are cations?

Answer 7

Positive ions

Question 8

What are anions?

Answer 8

Negative ions

Question 9

Which ions are attracted to the cathode?

Answer 9

Positive ions, cations

Question 10

Which ions are attracted to the anode?

Answer 10

Negative ions, anions

Question 11

Why must the substance being broken down be molten or dissolved?

Answer 11

In ionic compounds, Ions are free to move when molten or dissolved and can conduct electricity.

Question 12

Can covalent or ionic compounds be broken down using electrolysis and why?

Answer 12

Ionic compounds can - they contain ions which, when dissolved or molten, can move through the lattice and conduct electricity.
Covalent compounds can’t - molecules aren’t charged

Question 13

What does electrolysis break down compounds into?

Answer 13

Elements

Question 14

What happens at the anode during molten electrolysis?

Answer 14

Non-metal ions lose electrons to form molecules

Question 15

What happens at the cathode during aqueous electrolysis?

Answer 15

Metal ions gain electrons to form atoms

Question 16

Write a half-equation for what forms at the cathode during molten electrolysis of lead (II) bromide (PbBr2)

Answer 16

Pb2+ + 2e- –> Pb

Question 17

Write a half-equation for what forms at the anode during molten electrolysis of lead (II) bromide (PbBr2)

Answer 17

2Br- –> Br2 + 2e-

Question 18

What is observed at the cathode and anode during the molten electrolysis of lead (II) bromide?

Answer 18

Cathode - shiny silver substance (Pb)
Anode - orange vapour given off (Br2)

Question 19

Describe the rules for which ion reacts at the anode during aqueous electrolysis

Answer 19

If a group 7 element is present, it is formed
If no group 7 element is produced, 02 is formed

Question 20

Describe the rules for which ion reacts at the cathode during aqueous electrolysis

Answer 20

If the metal is less reactive than hydrogen, it will be formed
If the metal is more reactive than hydrogen, hydrogen is formed
The least reactive element is formed

Question 21

Which metals are less reactive than hydrogen?

Answer 21

Gold, silver, copper, platinum

Question 22

What happens to the ions that aren’t formed at the electrodes during aqueous electrolysis?

Answer 22

They remain leftover in the solution as 3rd product

Question 23

Write a half equation for what forms at the anode during the aqueous electrolysis of NaCl

Answer 23

2Cl- –> Cl2 +2e-

Question 24

Write a half equation for what forms at the cathode during the aqueous electrolysis of NaCl

Answer 24

2H+ + 2e- —> H2

Question 25

Why would solutions used for aqueous solutions contain H+ and OH - ions?

Answer 25

OH- and H+ ions are present in water, which is present in solutions

Question 26

Observations at anode and cathode during aqueous electrolysis of NaCl

Answer 26

Anode - Bubbles of green gas (Cl2) Cathode - Bubbles of colourless gas (H2)

Question 27

Write a half equation for what forms at the anode during aqueous electrolysis of copper (II) sulfate

Answer 27

4OH - --> O2 + 2H2O + 4e- Oxygen is produced

Question 28

Write a half equation for what forms at the cathode during aqueous electrolysis of copper (II) sulfate

Answer 28

Cu2+ + 2e- ----> Cu

Question 29

Write a half equation for the formation of oxygen during aqueous electrolysis

Answer 29

4OH- ---> O2 + H2O + 4e-

Question 30

Observations at anode and cathode during aqueous electrolysis of CuSO4

Answer 30

Anode - Bubbles of colourless gas (O2) Cathode - Pink, orange solid (Cu)

Question 31

Write a half equation for what forms at the cathode during aqueous electrolysis of dilute sulfuric acid

Answer 31

2H+ + 2e- ---> H2

Question 32

Write a half equation for what forms at the cathode during aqueous electrolysis of dilute sulfuric acid

Answer 32

4OH- --> O2 +H2O + 4e-

Question 33

If H+ was formed at the cathode during aqueous electrolysis, what colour would the universal indicator turn at the cathode?

Answer 33

Red