Electrolysis (chemical changes)

Question 1

What is electrolysis?

Answer 1

• Electrolysis is the use of electrical current to break down compounds containing ions into the constituent elements.
• During electrolysis: negatively charged ions move to the anode (positive electrode) and positively charged ions move to the cathode (negative electrode).

Question 2

What are the conditions for ionic compounds to conduct electricity?

Answer 2

• Ionic substances can only conduct electricity when they are molten or dissolved in water.

Question 3

What is an electrolyte?

Answer 3

• The substance being broken down is called the electrolyte.

Question 4

What are electrodes?

Answer 4

• The electrodes are made from solids that conduct electricity.

Question 5

What needs to be considered during the electrolysis of molten ionic compounds?

Answer 5

• For the electrolysis of molten ionic compounds, the electrodes must be inert so that they do not react with the electrolyte or the products.

Question 6

What is oxidation and reduction?

Answer 6

• Reduction occurs when positively charged ions gain electrons at the negative electrode.
• Oxidation occurs when negatively charged ions lose electrons at the positive electrode.

Question 7

What is a problem with using electrolysis to extract metals?

Answer 7

• Electrolysis requires a lot of heat and electrical energy, making it an expensive process.

Question 8

What is the condition for a metal to be extracted from its ore using electrolysis?

Answer 8

• Metals that are more reactive than carbon can be extracted from their ores using electrolysis.

Question 9

How is aluminium extracted from its ore using electrolysis?

Answer 9

• Aluminium is obtained by the electrolysis of aluminium oxide that has been mixed with cryolite (a compound of aluminium).
• Cryolite lowers the melting point of the aluminium oxide, meaning less energy is needed (cheaper energy costs).
• Aluminium forms at the negative electrode.
• Oxygen gas is forms at the positive carbon electrode and reacts with the carbon, forming carbon dioxide. This wears away the positive electrode, which is replaced regularly.

Question 10

Why is it harder to predict the products of the electrolysis of ionic compounds dissolved in water to form aqueous solutions?

Answer 10

• The water molecules break down to form hydroxide ions and hydrogen ions.

Question 11

What is produced at the negative electrode during the electrolysis of aqueous solutions?

Answer 11

• Hydrogen is produced if the metal is more reactive than hydrogen
• The metal is produced is the metal is less reactive than hydrogen.

Question 12

What is produced at the positive electrode during the electrolysis of aqueous solutions?

Answer 12

• Oxygen is produced unless the solution contains halide ions.
• If halide ions are present, then the halogen is produced