1.55-1.60 Electrolysis

Why are covalent compounds unable to conduct electricity?

They have no freely moving charged particles

What is electric current?

Flow of charged particles

What is sulfur hexafluoride (a dense gas) used to insulate?

Sulfur hexafluoride insulates electrical transformers

What covalent substances are also used in electrical equipment?

Silicone oils and liquid hydrocarbons

When can ionic compounds conduct electricity?

When molten or in solution

What are cations?

Positively charged ions

What are anions?

Negatively charged ions

During electrolysis, where do cations migrate towards?

Towards the negatively charged electrode, the cathode

During electrolysis, where do anions migrate towards?

Towards the positively charged electrode, the anode

What is a binary ionic compound?

A compound of two elements joined together by ionic bonding

In an ionic compound’s electrolysis, what will the cathode product always be and what will the anode product always be?

The cathode product will always be the metal.
The anode product will always be the non-metal

What is the method to the electrolysis of molten lead (II) bromide?

Fill in the gaps:

1. Add lead(II) bromide into a [ ] and [ ] so it will turn molten, allowing ions to be free to move and conduct an electric charge

2. Add two [ ] [ ] as the electrodes and connect this to a power pack or battery

3. Turn on the power pack or battery and allow electrolysis to take place

1. Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge

2. Add two graphite rods as the electrodes and connect this to a power pack or battery

3. Turn on the power pack or battery and allow electrolysis to take place

What happens CHEMICALLY at the anode in the electrolysis of molten lead (II) bromide?

Negative bromide ions move to the anode, losing two electrons to form bromine molecules

What happens VISUALLY at the anode in the electrolysis of molten lead (II) bromide?

Bubbling at the anode as brown bromine gas is given off

What happens CHEMICALLY at the cathode in the electrolysis of molten lead (II) bromide?

Positive lead ions move to the cathode and gain electrons to form grey lead metal

What happens VISUALLY at the cathode in the electrolysis of molten lead (II) bromide?

The grey lead metal deposits on the bottom of the electrode

Is the cathode the negative or positive electrode?

The negative electrode

What will aqueous solutions always contain?

Water molecules

What happens in the electrolysis of aqueous solutions?

Water molecules dissociate, producing H+ and OH- ions

During electrolysis of aqueous solutions, ions from the compound and ions from the water react together forming an…

Electrolyte

What is attracted to the anode in aqueous solution electrolysis?

All negatively charged ions (OH- and non-metal ions)

What are examples of halide ions?

Chloride, Bromide, Iodide

What happens with halide ions at the anode?

Halide ions lose electrons and form a halogen (chlorine, bromine or iodine)

If there are no halide ions present at the anode, what happens with hydroxide?

OH- is discharged at the anode, losing electrons and forming oxygen

What is attracted to the cathode in aqueous solution electrolysis?

All positively charged ions (H+ and metal ions), but only one will gain electrons

If, at the cathode, the metal is above hydrogen in the reactivity series, what will be produced?

Hydrogen will be produced and bubbling will be seen at the cathode
→ This is because more reactive ions will remain in solution, causing the least reactive ion to be discharged

What can be used to collect gases in electrolysis?

Inverted test tubes

What are the electrodes made from and why?

Graphite, as it is inert and does not interfere with the electrolysis reactions

What is oxidation?

When a substance loses electrons

What is reduction?

When a substance gains electrons

In the electrolysis of dilute sulfuric acid, what is the half equation at the anode?

2H₂O – 4e^– ⟶ O₂  +  4H⁺   

^Oxidation

In the electrolysis of molten lead(II) bromide, what is the half equation at the cathode?

Pb²⁺ + 2e^– ⟶ Pb         

Reduction

Do acidic solutions contain OH- ions?

No

If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint, the gas is…

Hydrogen

If the gas produced at the anode [ ] [ ] [ ] [ ] [ ] [ ] a sample of the gas, the gas is oxygen

If the gas produced at the anode relights a glowing splint dipped into a sample of the gas, the gas is oxygen

If the anode gas [ ] a piece of litmus paper, [ ] has been produced

If the anode gas bleaches a piece of litmus paper, chlorine has been produced

What is the cathode observation in sodium chloride electrolysis?

Colourless gas evolved which goes ‘pop’ with a lighted splint (hydrogen)

What is the anode observation in sodium chloride electrolysis?

Gas evolved which bleaches litmus paper (chlorine)

What does sodium chloride (aq) produce at the cathode and the anode? And what does it leave behind in solution?

Hydrogen at the cathode, chlorine at the anode. Sodium hydroxide in solution

What is the cathode observation in dilute sulfuric acid electrolysis?

Colourless gas evolved which goes 'pop' with a lighted splint

What is the anode observation in dilute sulfuric acid electrolysis?

Colourless gas evolved which relights a glowing splint

What does dilute sulfuric acid produce at the cathode and anode?

Hydrogen at the cathode, oxygen at the anode

What is the cathode observation in copper (II) sulfate electrolysis?

Pink-brown deposit seen on the electrode

What is the anode observation in copper (II) sulfate electrolysis?

Colourless gas evolved which relights a glowing splint

What does copper(II) sulfate (aq) produce at the cathode and the anode?

Copper at the cathode, oxygen at the anode