13 SECTION B – Module C3 5
Harneet and Mike investigate the reaction between sodium thiosulfate, Na2S2O3, and hydrochloric acid, HCl.
Sodium chloride NaCl, sulfur dioxide SO2, sulfur S and water H2O are made.
(a) Write a balanced symbol equation for this reaction. .............................................................................................................................................. [2]
(b) Look at the diagram. It shows their experiment. side view
top view cross
50 cm3
beaker containing sodium thiosulfate solution and 5 cm3 hydrochloric acid
paper
paper with cross
Harneet and Mike look down at the cross.
The liquid in the beaker goes cloudy.
After a time they cannot see the cross on the paper.
Harneet and Mike measure this time. This is the reaction time.
They do the experiment at four different temperatures.
They repeat the experiment at each temperature.
Look at their results.
Temperature in °C
Reaction time in seconds 1st
2nd
20
51.9
48.2
30
39.7
40.1
40
29.2
27.9
50
16.7
17.4
At which temperature is the reaction fastest? .............................................................................................................................................. [1]
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