5.2 Required practical: temperature changes
5 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Why is a polystyrene cup used instead of a glass beaker?
Choose one answer.
Correct Not quite: the answer is It reduces energy loss to the surroundings
Mark scheme
B
Model answer
B: polystyrene is a good insulator, so less energy is lost to the surroundings.
Give the independent variable and two control variables in this investigation.
Mark scheme
- independent: volume of sodium hydroxide added (1)
- any two control: volume of acid, concentration of acid, concentration of alkali, starting temperature (2)
Model answer
The independent variable is the volume of sodium hydroxide. Control variables include the volume and the concentration of the hydrochloric acid.
Explain why the highest temperature falls slightly after the acid has been neutralised.
Mark scheme
- no more reaction / no more energy released (1)
- the added alkali is cooler / absorbs energy from the mixture (1)
Model answer
Once the acid is used up, no more energy is released; the extra cool alkali absorbs energy, so the temperature drops.
Suggest one improvement to reduce energy losses in this experiment, and explain it.
Mark scheme
- use a lid / insulate the cup / use a thicker cup (1)
- reduces energy transferred to the surroundings (1)
Model answer
Put a lid on the cup, to reduce the energy lost to the air by evaporation and convection.
The two lines of best fit on the student's graph cross at 25 cm3 of sodium hydroxide.
What does this volume tell you?
Mark scheme
- the volume of alkali that exactly neutralises the acid (1)
Model answer
It is the volume of sodium hydroxide needed to exactly neutralise the acid, where the most energy has been released.
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