Question 5
FA student reacts equal masses of pure calcium carbonate with hydrochloric acid in two experiments, P and Q. The acid is in excess in both experiments. Gas volumes are measured at the same temperature and pressure. There are no leaks.
The graph shows the results. The axes have no numerical scale.
a.[3]
The student writes, "P produces more gas because its curve is higher, so more calcium carbonate must have reacted in P."
Evaluate this statement using both the shapes and the final levels of the curves.
b.[4]
The student used powdered calcium carbonate in P and large chips in Q. However, the acid in P was also more concentrated than the acid in Q.
Explain why the experiments do not establish the effect of particle size alone. Describe how to change the comparison, including two other quantities that should be controlled.
c.[3]
In a repeat with equal acid concentrations, powdered calcium carbonate still produces the steeper initial curve. Explain this difference using collision theory.
8.1 Rates of reaction Questions
54 exam-style questions on Edexcel GCSE Chemistry 8.1 Rates of reaction, covering 8.1.1 Measuring and interpreting rates of reaction, 8.1.2 Collision theory and the factors affecting rate, and 8.1.3 Catalysts and enzymes. Each one has a worked solution and a mark scheme showing where the marks go.