49ºC

In this experiment, hydrochloric acid and sodium thiosulfate are mixed. One product of the reaction is a precipitate of sulfur. As the reaction proceeds, this will obscure a cross drawn underneath the flask. The time taken to do this gives a measure of the rate of reaction. At different temperatures, the reaction will go at different speeds. Another product is sulfur dioxide, which is toxic.

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18ºC

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42ºC

Demo

29ºC

demo

29ºC

18ºC

42ºC

49ºC

18ºC

The disappearing cross experiment

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + SO2(g) + S(s)

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Measuring the average rate of reaction

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