Investigating Temperature Changes
Build confidence in Investigating Temperature Changes for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. The required practical measures temperature change in a polystyrene cup to classify reactions as exothermic or endothermic.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
This required practical investigates the temperature change during a reaction, most commonly the neutralisation of hydrochloric acid with sodium hydroxide.
Measure a fixed volume of acid into a polystyrene cup and record its starting temperature. Add a measured volume of alkali, stir, and record the highest temperature reached. Repeat with different volumes of alkali.
The polystyrene cup and lid reduce heat loss to the surroundings, which is the main source of error. Insulating the cup and using a lid improves accuracy. The volume of alkali giving the greatest temperature rise is the neutralisation point.
Revision notes
The method
Measure a fixed volume of acid into a polystyrene cup and record the starting temperature.
Add a measured volume of alkali, stir, and record the highest temperature reached. Repeat with increasing volumes of alkali, recording the maximum temperature each time.
Reducing heat loss
A polystyrene cup insulates the reaction mixture, and a lid reduces heat loss from the surface.
Placing the cup inside a beaker adds further insulation. Heat loss to the surroundings is the main source of error, so these precautions matter.
Interpreting results
Plot temperature rise against volume of alkali added.
The temperature rises to a maximum and then falls as excess cold alkali is added. The volume at the maximum is the point at which neutralisation is complete.
Key points
- Use a polystyrene cup to reduce heat loss.
- Record the starting temperature before adding.
- Record the highest temperature reached.
- A lid further reduces heat loss.
- The greatest temperature rise is the neutralisation point.
- Heat loss to the surroundings is the main error.
Worked examples
Example 1
Explain why a polystyrene cup is used rather than a glass beaker. [2 marks]
Model answer
Polystyrene is a good insulator (1 mark), so it reduces heat loss to the surroundings and gives a more accurate temperature rise (1 mark).
Example 2
Explain why a lid is placed on the cup. [2 marks]
Model answer
The lid reduces heat loss from the surface of the liquid (1 mark), so more of the energy released stays in the mixture and the measured temperature rise is closer to the true value (1 mark).
Example 3
Explain what the maximum temperature rise indicates. [2 marks]
Model answer
It shows the volume of alkali at which neutralisation is complete (1 mark), because adding more alkali after that point only cools the mixture rather than releasing further energy (1 mark).
Common mistakes
Using a glass beaker.
Glass conducts heat, so more energy is lost and the measured rise is too low.
Recording the final temperature rather than the highest.
The mixture begins cooling immediately, so the maximum must be recorded.
Forgetting the lid.
Heat loss from the surface is significant and reduces accuracy.
Not recording a starting temperature.
The rise cannot be calculated without it.
Exam tips
- Name polystyrene and explain it as an insulator.
- Record the highest temperature, not the final one.
- Mention both the cup and the lid when asked about accuracy.
- Identify heat loss as the main source of error.
Key terms
- Insulator
- A material that reduces heat transfer.
- Temperature rise
- The difference between starting and maximum temperature.
- Neutralisation point
- The volume at which the acid is exactly neutralised.
- Heat loss
- Energy transferred to the surroundings, reducing accuracy.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.