C5

Question 1

State and explain the conditions used in the contact process

Answer 1

• 450’C (temperature) - decreasing the temperature increases the yield because the forward reaction is exothermic, but decreases the rate of reaction, so a compromise of 450’C is used
• Atmospheric pressure - at atmospheric pressure, the position of equilibrium is already far to the right, so almost all of the reactants are converted into sulfur trioxide. A higher pressure is not used because it would not provide a great enough increase in yield to be worth the extra cost
• Vanadium oxide (V2O5) catalyst - increases the rate of reaction without affecting the position of equilibrium, remains unchanged at the end of the reaction

Question 2

Compare the pH of a strong and weak acid at the same concentration

Answer 2

The pH of a strong acid will be lower

Question 3

State ionic equations for the ionisation of hydrochloric and ethanoic acid

Answer 3

HCl -> H+ + Cl-

CH3COOH CH3COO- + H+

Question 4

Explain why strong acids are more conductive than weak acids

Answer 4

Because strong acids contain a greater concentration of hydrogen ions to carry the charge through the acid

Question 5

Explain why a strong and weak acid have different rates of reaction but produce the same volume of gas

Answer 5

Because:

• Strong acids ionise fully in solution, releasing a high concentration of hydrogen ions. This high concentration of hydrogen ions provides a high rate of reaction.
• Weak acids partially ionise in solution, forming in equilibrium mixture. As hydrogen ions are used up, more are released into the solution, until all of the acid has reacted. The initial concentration of hydrogen ions after ionisation is lower than in strong acids, so the rate of reaction is lower.

Question 6

Explain how to carry out a lab experiment to make an insoluble salt

Answer 6

1. Mix the 2 solutions together to form a precipitate (insoluble compound)
2. Separate the compound from the mixture using filter paper and a filter funnel
3. Wash the insoluble compound with water while it is on the filter paper
4. Dry the insoluble compound in a warm oven