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This question is about sulfuric acid and sulfates - AQA - GCSE Chemistry - Question 5 - 2017 - Paper 3
Question 5
This question is about sulfuric acid and sulfates. One reaction in the industrial production of sulfuric acid is: $$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$$... show full transcript
Worked Solution & Example Answer:This question is about sulfuric acid and sulfates - AQA - GCSE Chemistry - Question 5 - 2017 - Paper 3
Step 1
Explain why a moderately high temperature, instead of a low temperature, is used for this reaction.
Answer
A moderately high temperature is used because it increases the reaction rate. Higher temperatures provide more energy to the reacting molecules, thus enhancing collision frequency and facilitating the reaction. However, this comes at the cost of yield because the forward reaction is exothermic. According to Le Chatelier's principle, increasing temperature favors the endothermic reaction; therefore, there is a need for compromise to balance rate and yield.
Step 2
Explain why you would expect this reaction to be carried out at high pressure.
Answer
The reaction is expected to be carried out at high pressure because high pressure increases the yield of products. The reaction involves gases, and according to Le Chatelier's principle, increasing pressure shifts the equilibrium toward the side with fewer gas molecules, which in this case is the products side (2 moles of SO₃) as opposed to the reactants side (3 moles of gas). Thus, higher pressure enhances the rate of formation of sulfur trioxide.
Step 3
Suggest one advantage, other than cost, of using atmospheric pressure and not a high pressure for this reaction.
Answer
One advantage of using atmospheric pressure instead of high pressure is safety. Operating at high pressures can be hazardous due to risks of leaks or explosions. Using atmospheric pressure makes the process safer and reduces the chances of pressure-related accidents.
Step 4
Describe how sodium hydroxide solution is used to distinguish between a solution of magnesium sulfate and a solution of aluminium sulfate.
Answer
When sodium hydroxide is added to a solution of magnesium sulfate, a white precipitate forms, indicating the presence of magnesium ions. In contrast, when added to aluminium sulfate, a similar white precipitate also forms. However, if excess sodium hydroxide is added to the aluminium sulfate solution, the precipitate dissolves, indicating the presence of aluminium ions. Therefore, the behavior of the precipitate in excess sodium hydroxide can be used to distinguish between the two sulfate solutions.