1. 1
   A student plans an experiment to measure the volume of gas produced when marble chips react with dilute hydrochloric acid over time, to investigate the rate of this reaction.

   (a)

   Which piece of apparatus should the student use to measure the volume of gas collected?

   [1 mark]

   • AGas syringe
   • BBalance
   • CThermometer
   • DBurette

   (b)

   The student wants to keep the results comparable across repeated experiments while varying the surface area of the marble chips. Which variable must the student control?

   [1 mark]

   • AThe size of the individual marble chips
   • BThe surface area of the marble chips
   • CThe concentration and volume of the hydrochloric acid used each time
   • DThe volume of gas produced

   (c)

   Suggest one advantage and one disadvantage of using the volume of gas produced (rather than the loss in mass of the reaction flask) as the method of monitoring this reaction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A separate group investigates the effect of temperature on the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid, timing how long it takes for a mark under the reaction flask to disappear from view as a precipitate of sulfur forms.

   (a)

   Which apparatus is essential for this method?

   [1 mark]

   • AA measuring cylinder only
   • BA gas syringe and a balance
   • CA burette and a volumetric pipette
   • DA stopwatch and a thermometer

   (b)

   The group repeats the experiment at several different temperatures, keeping the concentrations and volumes of both solutions the same each time. Why is it important to control the concentrations and volumes in this way?

   [1 mark]

   • ASo that the reaction produces a different gas at each temperature
   • BSo that temperature is the only variable affecting the rate, making the comparison fair
   • CSo that the total volume of gas produced can be measured accurately
   • DSo that a precipitate no longer forms during the reaction

   (c)

   Suggest one limitation of using 'time for the mark to disappear' as the measured quantity in this experiment, and suggest one way the group could improve the reliability of their results.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is asked to design an experiment to investigate the effect of surface area on the rate of reaction between calcium carbonate and dilute hydrochloric acid, monitoring the loss in mass of the reaction flask over time using a balance. The student plans to plug the top of the flask loosely with cotton wool during the experiment.

   (a)

   State three variables the student must keep constant to ensure a fair test.

   [3 marks]

   (b)

   Explain the purpose of loosely plugging the top of the flask with cotton wool in this experiment, and describe how the student should use their results to compare the rates of reaction for the different surface areas tested.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school laboratory technician is preparing an experiment for students to investigate how changing the concentration of hydrochloric acid affects its rate of reaction with excess magnesium ribbon, using the volume of hydrogen gas collected in a gas syringe over time.

   (a)

   Describe, in detail, how the experiment should be designed, including the apparatus needed, the variables that must be controlled, and how the results should be recorded and analysed to draw a valid conclusion.

   [6 marks]

   (b)

   After running the experiment, several student groups obtain slightly different initial rates for the same concentration of acid. Evaluate possible sources of error or limitation in this experimental method, and suggest specific improvements the technician could make to increase the reliability and accuracy of the class's results.

   [6 marks]

   Total for question 4: 12 marks

End of questions