Home / AS & A Level Chemistry 8.3 Homogeneous and heterogeneous catalysts Exam Style Practice Questions Paper 1
When two aqueous solutions are mixed, the reaction between them is very slow.
An effective catalyst is added to the mixture without any change in temperature.
Which statement about this catalyst is correct?
Correct Answer: \( \boxed{\mathrm{C}} \)
A catalyst provides an alternative reaction pathway with a lower activation energy.
Since the temperature is unchanged, the average kinetic energy and the Maxwell-Boltzmann energy distribution remain unchanged.
Lowering the activation energy means a greater proportion of collisions are successful, so more reactant particles react per unit time.
Therefore, the correct answer is (C).
In the diagram, curve X was obtained by measuring the volume of oxygen produced during the decomposition of \(100\,\mathrm{cm^3}\) of \(1.0\,\mathrm{mol\,dm^{-3}}\) hydrogen peroxide. A catalyst of manganese(IV) oxide was used.
Which alteration to the original experimental conditions would produce curve Y?
Correct Answer: \( \boxed{\mathrm{B}} \)
Curve Y reaches a higher final volume of oxygen but has a lower initial rate than curve X.
Adding some \(0.1\,\mathrm{mol\,dm^{-3}}\) hydrogen peroxide increases the total amount of hydrogen peroxide present, so more oxygen is eventually produced.
However, because the added solution is much more dilute, the overall concentration of hydrogen peroxide decreases, giving a slower initial reaction rate.
Adding more catalyst or increasing the temperature would increase the reaction rate but would not change the final volume of oxygen. Adding water would decrease the rate but leave the final volume unchanged.
Therefore, the correct answer is (B).
Solutions X and Y both have a concentration of 0.10 mol dm–3. A fixed volume of solution X is added to a conical flask, and solution Y is added from a burette to the conical flask. A titration is performed.
The diagram shows the pH titration curve for the acid–base reaction between the solutions.
What are solutions X and Y?
Ans: A
The curve starts at a high pH (~11-13), indicating the solution in the flask (X) is a base. The steep drop at the equivalence point is characteristic of a strong acid-strong base titration. Ammonia is a weak base and nitric acid is a strong acid. The initial high pH and the shape of the curve match the titration of a weak base (ammonia) with a strong acid (nitric acid).