By accepting you will be accessing a service provided by a third-party external to https://mychem.co.uk/

Sodium thiosulfate

You will need:
  • Access to boling water
  • Jam jar
  • 5 x v. small identical transparent beakers or test tubes
  • test tube
  • plain paper and a pencil
  • conductivity tester ( torch and cables assembled to do the testing)
  • petri dish
  • supply of sodium thiosulfate crystals (DDS)
  • Measuring cylinders or syringe (10 - 20 ml)
  • about 50ml of vinegar (white is best but not important)

 What we did..

We prepared four separate beakers with differing numbers of crystals on sodium thiosulfate crystals in them.

We added 10 ml water to each of the beakers and swirled the beaker so that the crystals dissolved completely.  We drew a cross on a piece of paper underneath each of the beakers. 

We added 5 ml vinegar to each of the beakers and stated the stopwatch. We measured the time it took for the reaction to obscure the pencil cross on  the paper.

 What we found out..

Numbers indicate the time in seconds taken for the solution to become so cloudy that the cross can no longer be seen on the paper.

number of  crystals used..... 30 20 105
MM 300 450 630did not change
OC5076120240

 The tekkie bit..

In this reaction the sodium thiosulfate solution decomposes as a result of the acid in the vinegar. When it decomposes - it produces tiny particles of sulfur. This appears as a white "cloud" - known as a precipitate. After a while this precipitate is so thick that the pencil cross can no longer be seen. Measuring the time taken for the cross to disappear in this way allows us to measure the rate of the reaction. The less time it takes the faster the rate. The longer the time the slower the rate.