electrolysis

What is electric current

Flow of charged particles. Usually electrons but can also mean ions

Why cant most covalent compounds conduct electricity

Because they have no freely moving charged particles to carry the current. (Acting as insulators)

Examples of covalent substances being used as electrical insulators

Sulfur hexafluoride is a dense gas used to insulate electrical transformers

Silicone oils and liquid hydrocarbons are also used in electrical equipment

When can ionic compounds conduct electricity

In a molten state or in solution (aqueous)

Why can ionic compounds conduct induct electricity in a molten state or in a solution

This is because they have ions that can move and carry charge. They cannot conduct electricity in a solid state as the ions are in fixed positions within the lattice and are unable to move.

Cartoons

Positively charged ions

K⁺, Mg²⁺, H⁺

Anions

Anions are negatively charged ions

Cl^-, O^2-, SO₄^2-

What happens in electrolysis

During electrolysis the electrons move from the anode towards the cathode. The cations within the electrolyte migrate towards the negatively charged electrode which is the cathode. Anions within the electrolyte migrate towards the positively charged electrode which is the anode.

Why are cations attracted to the cathode and anions attracted to the anode

Because opposites attract

What is a binary ionic compound

Compounds consisting of just two elements joined together by ionic bonding

What happens when a binary ionic compounds conduct induct is heated

They become molten and can conduct electricity as ions can move freely and carry the charge.

Is the cathode or anode product metal

The cathode product will always be the metal and the product formed at the anode will be non metal

Describe the electrolysis of lead bromide

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 at the anode

• Negative bromide ions move to the positive electrode (anode)

• At the anode, they lose two electrons to form bromine molecules

• There is bubbling at the anode as brown bromine gas is given off

What happens at the catnode

• Positive lead ions move to the negative electrode (cathode)

• At the cathode they gain electrons to form grey lead metal 

• The lead deposits on the bottom of the electrode

What is produced at the anode

• Negatively charged OH- ions and non metals ions go to anode

• If halide ions like (Cl-, Br-) are present then the halide ion is discharged at the anode losing electrons and forms a halogen

• if no halide ions then OH- is discharged, loses electrons and forms oxygen

• In both cases the other negative ion remains in solution

What is produced at the cathode

• Positively charged H+ ions and metal ions are attracted to the cathode but only one gains electrons

• Either hydrogen gas or metal will be produced

• The least reactive one will be reduced. If the metal is more reactive that hydrogen, then hydrogen will be produced and bubbling will be seen at the cathode

Electrolysis method

1. Add the aqueous solution to a beaker and cover the electrodes with the solution

2. Invert two small test tubes to collect any gaseous products

3. Connect the electrodes to a power pack or battery

4. Turn on battery or power pack

5. Electrolysis happens, observations and gas can be tested

Cathode hydrogen test

Burns with a pop when a sample is lit with a lighted splint, the gas is hydrogen

Anode oxygen test

Relights a glowing splint dipped into a sample of the gas, the gas is oxygen

Chlorine test

Bleaches a piece of litmus paper, chlorine has been produced

What reaction takes place at the cathode

Positively charged ions gain electrons so reduction

What reaction takes place at anode

At the anode negatively charged ions lose electrons so oxidised

What is the ammonia gas test

place damp red litmus paper in the gas; it will turn blue, indicating the alkaline nature of ammonia

What is the carbon dioxide gas test

bubbling the gas through limewater, which is a calcium hydroxide solution, and observing a positive result: the limewater turns milky or cloudy