My Aim is to see how concentration of acid will affect the time it takes for Sodium Thiosulphate to become cloudy and make a cross below it to disappear.

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GCSE Coursework

                Philip Stirups

Disappearing Cross Experiment

Aim:  My Aim is to see how concentration of acid will affect the time it takes for Sodium Thiosulphate to become cloudy and make a cross below it to disappear.

Method:

Apparatus

Hydrochloric Acid

Sodium Thiosulphate

Distilled Water

250cm ³ Beaker- I need a beaker big enough to see the cross and although the 100cm³ would be perfect volume wise I would prefer to use a bigger one so I can fit the cross under it and also be able to pour the reactants into it without any spillage

100cm ³ Measuring Cylinder- I have decided to use this cylinder for the Sodium Thiosulphate. I am only using 50cm ³ each time but I would prefer to use one in which I only have to measure to half way as opposed to using a 50cm ³ Measuring Cylinder and having to measure it right to the top. It will be easier to measure

10cm ³ Measuring Cylinder- This is the smallest Measuring Cylinder available. I will use this to measure out the Hydrochloric acid and Distilled water because there volume together will equal 10cm³. If I use a  50cm³ Measuring cylinder, I won’t be able to get a good enough accuracy.

Stopwatch- For timing the experiment

Pipette for measuring out accurately and piping back excess Hydrochloric acid

Piece of paper with a black cross on it like this: To find out when the experiment has ended. It is dark and thick because I want to clearly see when the experiment has finished

Paper towels: For washing beakers and measuring cylinders out.

  1. Put the black cross underneath the 250cm ³ Beaker, leave this on the side.
  2. Measure out 50cm ³ of Sodium Thiosulphate in the 100cm ³ Measuring cylinder  and pour into the 250cm ³  beaker
  3. In the other 100cm ³ measuring cylinder. The volume of Hydrochloric acid +volume of distilled water add up to 10cm ³. Here is a table
  4. Put the black cross underneath the 250cm ³ Beaker, leave this on the side.
  5. Measure out 50cm ³ of Sodium Thiosulphate in the 100cm ³ Measuring cylinder  and pour into the 250cm ³  beaker
  6. In the other 100cm ³ measuring cylinder. The volume of Hydrochloric acid +volume of distilled water add up to 10cm ³. Here is a table

                 

From my pilot

I have based my prediction on my pilot experiment. The reason I have mentioned giving the 250cm ³ beaker a thorough washing is because in my pilot one of my results became irregular. The reason this was like this is because in the pilot we were just testing and didn’t consider that washing out the beaker thoroughly we only gave it a quick rinse and we couldn’t have rinsed it out properly because one of the experiments was a lot quicker than the other ones. From this I have learned that even a little bit of solution left in the beaker from the last experiment will ruin it so I will need to take extra precaution to make sure the beaker is clean as has no solution left at the bottom. This leads me to think that the more acid you have in the solution the quicker it will be. Also having not cleaned it up properly will mean that I can not efficiently measure concentration because it will change with the few cm³ left. So I must pay a lot of attention to cleaning them out properly because it will ruin the concentration and the results if I don’t. One problem with using such a little amount of acid to change by each time is that I will have to be very careful about washing them out

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        If I had an infinite amount of time I would use separate beakers for each experiment but because I am doing each one three times I don’t think the equipment will be available to me so I will just have to be very cautious.

        .In my pilot I used higher quantities of acid but I discovered that doing this is a waste of time and wasteful because you can make the concentration differ however much acid and water you choose to vary. I used high amount of acids but then discovered the overall solution had the same concentration so I ...

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