Page 80 - Science Coursebook

Unit 5
Unit 5 End of unit questions

5.1 Choose one of the following words or phrases to match each description.
Each may be used once, more than once, or not at all.
burning decreases endothermic evaporation
exothermic increases melting ice
magnesium ribbon placed in hydrochloric acid
sodium hydrogencarbonate added to citric acid
a An example of a chemical reaction where heat is given out.
b An example of an endothermic reaction.
c The temperature in an endothermic reaction.
d An example of an endothermic process.
e The type of reaction between calcium and water. [5]

5.2 Vishal and Manish are carrying out an investigation into the heat given off when
they add pieces of calcium to water.
They both use 10 cm water and add pieces of calcium.
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These are Vishal’s results:

Mass of calcium added / g Start temperature / °C Final temperature / °C
1 19 20
2 19 21
3 19 22
4 19 23

These are Manish’s results:

Mass of calcium added / g Start temperature / °C Final temperature / °C
1 21 22
2 21 22
3 21 24
4 21 25

a What trend is shown by both sets of results? [1]
b Predict what would happen if 5 g of calcium were added. [1]
c Using Vishal’s results, calculate the temperature change for each mass of
calcium used. Then do the same for Manish’s results. [2]
d Now construct a summary table, showing the mean (average) temperature
rise for each mass of calcium. (Your table does not need to show the start

and final temperatures.) [2]
e Vishal and Manish plot a graph of their results. Which variable and unit
should they put on the horizontal axis? [1]
f Which variable and unit should they put on the vertical axis? [1]
g The boys carried out a third set of experiments, using 20 cm of water instead
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of 10 cm . Could they use these results to add to the fi rst two sets, to
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calculate an average temperature change? Explain your answer. [2]

78 5 Energy changes