Measuring enthalpy changes of reactions
2 marks · HardA student wants to measure the enthalpy change for the reaction between hydrochloric acid and sodium carbonate solution using a polystyrene cup calorimeter.
State two steps the student should follow to ensure the experiment produces reliable results.
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Also accept: Repeat the experiment and take an average; Use a lid to reduce heat loss; Stir the mixture thoroughly; Use the same volumes of solutions each time; Ensure both solutions are at the same starting temperature
Common mistakes: Not mentioning control of variables such as starting temperature or volume
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States one correct step to ensure reliability (e.g., repeat and average, use of lid, stir mixture, equal volumes, same starting temperature, etc.)
B2 · 1 mark · States a second correct step, different from the first.
Worked solution
Two steps the student should follow are:
1. Use a lid on the calorimeter to reduce heat loss to the surroundings.
2. Repeat the experiment and take an average of the temperature changes.