Temperature Changes
Q1.
A student investigated the energy change occurring in the endothermic reaction between potassium hydrogencarbonate and hydrochloric acid.
Figure 1 shows the apparatus used.
 
This is the method used.
1. Measure 50 cm3 hydrochloric acid into a glass beaker.
2. Measure 1.0 g of potassium hydrogencarbonate.
3. Add the potassium hydrogencarbonate to the hydrochloric acid.
4. Stir until all the potassium hydrogencarbonate has reacted.
5. Record the lowest temperature reached.
6. Repeat steps 1‒5 two more times.
7. Repeat steps 1‒6 with different masses of potassium hydrogencarbonate.

(a)     Which is the most suitable apparatus to use to measure 50 cm3 of hydrochloric acid?
Tick (✔) one box.
 
Balance		
Conical flask		
Gas syringe		
Measuring cylinder		
(1)
(b)     The student used a glass beaker for the reaction.
Suggest one change to the apparatus that would improve the accuracy of the results.
Give a reason for your answer.
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(2)
(c)     Which two variables should the student keep the same to make this a fair test?
Tick two boxes.
 
Mass of potassium hydrogencarbonate		
Same balance		
Same thermometer		
Starting temperature of hydrochloric acid		
Volume of hydrochloric acid		
(2)
(d)     Figure 2 shows part of the thermometer used to measure the temperature.
 
What is the temperature reading on the thermometer?
Temperature = ___________ °C
(1)
The table shows a set of results.
 
 	Test 1	Test 2	Test 3	
Lowest temperature in °C	16.1	15.8	15.9	
(e)     What is the range of the lowest temperature?
From _________ °C to _________ °C
(1)
(f)      Calculate the mean lowest temperature.
Use the table above.
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Mean lowest temperature = ______________________ °C
(2)
(g)     How do the results show that the reaction is endothermic?
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(1)
The graph shows the student’s results.
 
(h)     Draw two straight lines of best fit on the graph above.
(2)
(i)      Describe how the lowest temperature changes as the mass of potassium hydrogencarbonate added increases.
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(3)
(Total 15 marks)