(1.55C-1.60C) Electrolysis

What is conductivity?

The characteristic of a material wherein it has charged particles (ions/electrons) that are free to move

Why do most covalent compounds not conduct electricity?

They have no free flowing charged particles

What are the charged particles in ionic compounds?

The ions

In which states can ionic compounds conduct electricity?

Molten or aqueous

Why can ionic compounds only conduct electricity in specific states?

When solid, the ions are fixed in an ionic lattice

When molten/aqueous, the ions can move

What are cations?

Positive ions

What are anions?

Negative ions

What is electrolysis?

The separation of an ionic compound

by passing an electric current through it

Describe the set-up of an electrolysis chamber + what happens during the process.

A cathode and an anode (made of inert graphite)

are placed in a container with molten/aqueous ionic compound.

A current is passed from anode → cathode (+ → -)

The anions collect at the anode

The cations collect at the the cathode

Which type of substances form at the cathode and anode?

metal at cathode

non-metal at anode

Describe the electrolysis of molten lead (||) bromide.

1. Add lead(||) bromide to a crucible and heat till molten.

2. Connect the chamber + add solution.

Pb²⁺ goes to cathode + gains 2 electrons forming Pb. Grey metal coating electrode.

Br^- goes to anode. Each one loses one electron. 2 ions → Br₂. Bubbling as gas given.

What is a key difference between the electrolysis of molten vs aqueous compounds?

Aqueous compounds will also contain water, so these ions need to be accounted for.

In an aqueous solution, what rules determine the products at the anode?

OH^- ions and non-metal ions go to the anode.

If halide ions are present, a halogen is formed.

If not, OH^- is discharged and forms oxygen.

The left over negative ion remains in solution.

In an aqueous solution, what rules determine the products at the cathode?

H+ and metal ions go to the cathode.

If the metal is above hydrogen in the reactivity series,

hydrogen is produced and bubbling is seen.

(the least reactive ion is discharged)

What happens in the electrolysis of aqueous sodium chloride?

Chlorine gas is produced at the anode.

Hydrogen gas is produced at the cathode.

NaOH remains in solution.

What happens in the electrolysis of aqueous sulfuric acid?

Hydrogen gas forms at the cathode.

Oxygen forms at the anode.

What happens in the electrolysis of aqueous copper(||) sulfate?

Copper forms at the cathode.

Oxygen forms at the anode.

What is oxidation?

The loss of electrons

What is reduction?

The gain of electrons

Where in electrolysis does oxidation/reduction occur?

At the electrodes

What is an electrolysis half-equation?

An equation that only contains the ion being discharged and the electrons discharging it.

Describe the practical to electrolyse aqueous solutions ‘+ identify the products.

1. Add the solution to the beaker + insert electrodes.

2. Invert 2 test tubes over the electrodes to collect any gas products.

3. Connect electrodes to battery bank

4. Record observation + test gases + test metal products.