To find out how the concentration of sodium thiosulphate affects the rate at which the acid turns cloudy.

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Ian Craddock 10/12

To find out how the concentration of sodium thiosulphate affects the rate at which the acid turns cloudy.

Variable: 

  • Temperature.
  • Size of cross.
  • Colour of cross.
  • Amount of acid.
  • Amount of sodium thiosulphate.
  • Size of beaker.

Prediction: By changing the concentration of the thiosulphate but keeping all other variables the same.

I think that the more thiosulphate the longer it will take the acid to turn cloudy.

If there is more acid to react with little thiosulphate it should take less time to turn cloudy.

Experimental plan: I will measure the time it takes for a cross on the tile under the beaker to vanish, with different amounts of sodium hyposulphite being added.

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I will keep the volume of fluid the same buy adding water, which is neutral, to the mixture.

Apparatus:

  • Tile
  • Beaker
  • 2 x measuring tubes
  • Marker pen
  • Sodium thiosulphate
  • Dilute hydrochloric acid
  • Water
  • Stop watch

Method:

  1. Place the beaker on top of the tile. (Look at diagram).
  2. Pour out 10ml of hydrochloric acid in to one measuring tube.  In the other put an amount of sodium thiosulphate and top it up to 25ml with water.
  3. Pour the 2 measuring tubes in to the beaker and start the stopwatch.
  4. When you can ...

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