1. 1
   A quarry laboratory technician reacts marble chips (calcium carbonate) with excess dilute hydrochloric acid in a conical flask, collecting the carbon dioxide gas produced in a gas syringe. The technician repeats the experiment using powdered marble of the same total mass in place of the chips, with all other conditions kept the same.

   (a)

   In one trial, 48 cm3 of gas is collected in the first 60 seconds of the reaction. What is the mean rate of reaction over this period?

   [1 mark]

   • A48 cm3 per second
   • B1.25 cm3 per second
   • C0.8 cm3 per second
   • D2880 cm3 per second

   (b)

   The technician repeats the experiment using powdered marble of the same total mass in place of the chips, keeping all other conditions the same. What effect would this change have on the rate of reaction?

   [1 mark]

   • AThe reaction would stop completely
   • BThe rate would decrease
   • CThe rate would stay exactly the same
   • DThe rate would increase

   (c)

   Using collision theory, explain why powdered marble reacts faster with the acid than marble chips of the same total mass.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An industrial chemical plant investigates the effect of temperature on reaction rate using sodium thiosulfate solution and dilute hydrochloric acid, timing how long it takes for a mark viewed through the solution to disappear as a precipitate forms. The experiment is repeated at 20 degrees Celsius, 35 degrees Celsius and 50 degrees Celsius, keeping all concentrations the same.

   (a)

   As the temperature increases, what happens to the rate of reaction?

   [1 mark]

   • AThe rate of reaction stays the same
   • BThe rate of reaction decreases
   • CThe rate of reaction increases
   • DThe reaction stops occurring

   (b)

   What happens to the time taken for the mark to disappear as the temperature of the reaction increases?

   [1 mark]

   • AThe time taken increases
   • BThe mark never disappears at higher temperatures
   • CThe time taken stays exactly the same
   • DThe time taken decreases

   (c)

   Using collision theory, explain why increasing the temperature of the reaction increases its rate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A food scientist studies the reaction between magnesium ribbon and dilute sulfuric acid at different acid concentrations, collecting the hydrogen gas produced in a gas syringe. The scientist repeats the experiment using acid of a higher concentration, 2.0 mol/dm3, keeping the mass of magnesium and all other conditions the same.

   (a)

   Using a concentration of 1.0 mol/dm3, 24 cm3 of gas is collected in the first 40 seconds. Calculate the mean rate of reaction over this period, giving the correct unit.

   [3 marks]

   (b)

   The scientist repeats the experiment using acid of a higher concentration, 2.0 mol/dm3, keeping the mass of magnesium and all other conditions the same. Using collision theory, explain why the reaction is faster at the higher acid concentration.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school laboratory group reacts calcium carbonate chips with excess dilute hydrochloric acid in a flask standing on a mass balance, recording the total mass of the flask and its contents as carbon dioxide gas escapes over several minutes.

   (a)

   A tangent drawn to the graph of mass lost against time at 15 seconds passes through the point (5 seconds, 0.4 g lost) and the point (25 seconds, 2.0 g lost). Calculate the gradient of this tangent and explain what the value represents.

   [6 marks]

   (b)

   Explain, in terms of collision theory, why the rate of this reaction (shown by the steepness of the mass-time graph) decreases as the reaction proceeds, becoming slowest just before the reaction finishes.

   [6 marks]

   Total for question 4: 12 marks

End of questions