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Chemistry practical

Rates of reaction: the disappearing cross

Time how long the cross takes to vanish at five concentrations of thiosulfate, and show the rate is proportional to concentration.

What you will do

  1. 01Measure sodium thiosulfate and water in measuring cylinders so they add up to 50 cm³.
  2. 02Pour both into the flask standing on the paper with the black cross.
  3. 03Add 5 cm³ of acid and start the stopwatch at once.
  4. 04Look down through the flask and stop the watch when the cross can no longer be seen.
  5. 05Tip the mixture away, rinse the flask, and repeat with different volumes.
  6. 06Calculate 1/t, plot it against the volume of thiosulfate, and draw your conclusion.