1. 1
   A student mixes 25 cm3 of dilute hydrochloric acid with 25 cm3 of dilute sodium hydroxide solution in an insulated polystyrene cup and records the temperature before and immediately after mixing. The temperature rises from 19°C to 26°C.

   (a)

   A student adds 25 cm3 of dilute hydrochloric acid to 25 cm3 of dilute sodium hydroxide solution in an insulated polystyrene cup, and the temperature rises from 19°C to 26°C. What piece of equipment must the student use to measure the temperature?

   [1 mark]

   • AA measuring cylinder
   • BA thermometer
   • CA balance
   • DA pipette

   (b)

   Why does the student use an insulated polystyrene cup rather than an open glass beaker for this experiment?

   [1 mark]

   • ATo reduce energy losses to the surroundings, giving a more accurate temperature change
   • BBecause glass beakers react with hydrochloric acid
   • CTo increase the rate of the neutralisation reaction
   • DBecause polystyrene is a catalyst for this reaction

   (c)

   State whether this reaction is exothermic or endothermic, giving a reason based on the temperature change, and name the type of reaction taking place between the acid and the alkali.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student adds a spatula of solid ammonium nitrate to 50 cm3 of water in an insulated polystyrene cup, stirring gently and recording the temperature before and after. The temperature falls from 21°C to 14°C.

   (a)

   A different student adds a spatula of solid ammonium nitrate to water in an insulated cup and records the temperature falling from 21°C to 14°C. What does this observation show about the reaction?

   [1 mark]

   • AIt is exothermic, because the temperature fell
   • BIt is exothermic, because energy is taken in from the surroundings
   • CIt is endothermic, because energy is taken in from the surroundings
   • DNo reaction has taken place, since the temperature fell

   (b)

   Which piece of apparatus should the student use to accurately measure out the 50 cm3 of water before adding the solid?

   [1 mark]

   • AA stopwatch
   • BA thermometer
   • CAn electronic mass balance for liquids only
   • DA measuring cylinder

   (c)

   Explain why the student stirs the mixture gently after adding the solid, and describe one way the student could improve the reliability of this result.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A group of students investigates the temperature change produced when different reactive metals react with dilute hydrochloric acid in an insulated polystyrene cup, in order to compare the energy released by each metal reacting with the acid.

   (a)

   A group of students investigates the temperature change when different metals react with dilute hydrochloric acid in an insulated cup. They react excess magnesium ribbon with 25 cm3 of dilute hydrochloric acid and record a temperature rise from 20°C to 45°C. Describe the method they should use to obtain a reliable temperature change for this reaction.

   [3 marks]

   (b)

   The students repeat the experiment using zinc instead of magnesium and obtain a smaller temperature rise, from 20°C to 31°C. Explain what this result suggests about the reaction of zinc with hydrochloric acid compared with magnesium, and identify a possible source of error that could affect the fairness of this comparison.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A college laboratory group is designing an investigation into how the concentration of hydrochloric acid affects the temperature change when it reacts with excess magnesium ribbon in an insulated container, aiming to draw a conclusion about energy released versus acid concentration.

   (a)

   Design a full experimental method to compare the energy released when three different concentrations of hydrochloric acid react with excess magnesium ribbon in solution, ensuring the comparison is fair and the results are reliable. Include the apparatus needed, the measurements to be taken, and the key variables to control.

   [6 marks]

   (b)

   Discuss the limitations of using a simple insulated cup method, as described above, to determine an accurate value for the energy released per mole of magnesium reacting, and suggest improvements that would make the calculated energy value more accurate.

   [6 marks]

   Total for question 4: 12 marks

End of questions