Topic 10 - Electrolytic Processes

Question 1

3.22 - What is an electrolyte?

Answer 1

Electrolytes are ionic substances with freely moving ions in the molten state or dissolved in water ( aqueous ).

Question 2

3.23 - Describe the process of electrolysis

Answer 2

In electrolysis, electrical energy from a d.c supply is transferred by electricity to decompose electrolytes.
Two electrodes are connected to a d.c current and placed in the electrolyte.

Question 3

3.24 - Explain the movement of ions in electrolysis

Answer 3

Positively charged cations move to the negatively charged cathode.
Negatively charged anions move to the positively charged anode.

Question 4

3.25 - Explain the formation of products in electrolysis with inert electrodes

Answer 4

In an aqueous ionic compound, there are the ions in the electrolyte and the ions in the water ( OH- / H+ ).
At the negative cathode - H+/Hydrogen is produced unless the positively charged metal ions in the ionic compound is less reactive than hydrogen, this would produce that metal. ( metals less reactive than H+ - Cu, Ag, Au, Pt )
At the positive anode - OH-/Oxygen is produced unless the negatively charged ions is a halide ion, this would produce a halogen.

Question 5

3.26 - Predict the products of electrolysis in the molten state

Answer 5

In molten state, there are no ions present except those in the ionic compound, therefore the cations ( + ) go to the cathode and the anions ( - ) go to the anode.

Question 6

3.27 - How do you explain and represent the reactions taking place in electrolysis at each electrode?

Answer 6

Using half equations:
Negative electrode - X+ + 2e- –> X, electrons gained so positive ions are reduced here.
Positive electrode - X- –> X + e-, electrons lost, so negative ions are oxidised here.

Question 7

3.28 - Explain oxidation and reduction

Answer 7

Oxidation - Loss of electrons
Reduction - Gain of electrons
OILRIG - Oxidation is loss, reduction is gain.

Question 8

3.29 - In which electrodes do oxidation and reduction take place?

Answer 8

Anode - Positive electrode so attracts negative ions, which lose electrons to have a neutral charge.
Cathode - Negative electrode so attracts positive ions, which gain electrons to become neutral.

Question 9

3.30/3.31 - How is copper purified using electrolysis?

Answer 9

Anode is a piece of impure copper and the cathode is made of pure copper.
Copper atoms in the anode lose electrons to become copper ions, then they dissolve in the electrolyte ( CuSO4 ) and moves to the cathode where pure copper is deposited. Impurities collect as a ‘ sludge ‘ under the anode and don’t form ions.
Cathode gains mass while the anode loses mass.

Question 10

3.31 - Core practical - How do you separate a copper sulfate electrolyte into its ions with inert electrodes?

Answer 10

With inert electrodes Cu is produced at the cathode as it is less reactive than hydrogen.
And at the anode, oxygen is formed as sulfate ions aren’t halide ions.