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I am going to do an investigation to find how changing the volume and the concentration of Hydrochloric acid effects the time taken for a solution of Sodium Thiosulphate and Hydrochloric acid to go cloudy and obscure a cross.

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Introduction

Investigation to find the consequences of changing the concentration Introduction I am going to do an investigation to find how changing the volume and the concentration of Hydrochloric acid effects the time taken for a solution of Sodium Thiosulphate and Hydrochloric acid to go cloudy and obscure a cross. Theory When Hydrochloric acid is added to Sodium Thiosulphate the solution goes cloudy because a precipitate of sulphur is produced as they react. A precipitate is created when two solutions are mixed and form a solid. Hydrochloric acid + Sodium Thiosulphate Sodium Chloride + Water + Sulphur Dioxide + Sulphur 2HCl(aq) + Na2S2O3(aq) 2NaCl(aq) + H2O(l) + SO2(g) + S(s) Concentration, temperature, surface area or a catalyst can change the rate of reaction. To change concentration you can add more water than acid to a solution to make a dilute solution or the other way round to make a concentrated solution. Changing concentration can mean there is more water than acid particles so less acid particles can bump into the Sodium Thiosulphate particles and react. ...read more.

Middle

Prediction I predict that the higher concentration of Hydrochloric acid added the sooner a precipitate will be created and the cross obscured. I believe this because the higher the concentration the more often the particles bump into each other causing the reaction to happen quicker so a precipitate will be created sooner. I predict that the higher the volume of Hydrochloric acid added the slower a precipitate would be formed. I believe this because there will be a greater volume of solution to go cloudy so it would take longer. Observations Volume of HCl /cm3 Volume of Na2S2O3 /cm3 Concentration of HCl /mole Concentration of Na2S2O3 /mole Time taken for cross to obscure /seconds 1st Time taken for cross to obscure /seconds 2nd Average time taken for cross to obscure /seconds 10 20 1 1 71 72 71.5 20 20 1 1 77 79 78 30 20 1 1 86 84 85 10 20 2 1 58 59 58.5 20 20 2 1 63 61 62 30 20 2 1 83 84 83.5 ...read more.

Conclusion

Dilute Solution Concentrated Solution Evaluation I thought the investigation was very successful. My predictions that the higher the concentration the quicker a precipitate forms, and the greater volume of Hydrochloric acid the longer the reaction takes to form a precipitate, were both found to be correct. This shows that to form a precipitate quickly then you need more Hydrochloric acid particles to bump into the Sodium thiosulphate particles. All of my results showed this to be true. If I had to repeat this experiment again I would keep the equipment the same because I believe the equipment I used was right for the experiment, and I would keep the method the same because I believe it worked well and couldn't be improved. I would however do more of each test so my results were more reliable and accurate, as it would allow for any anomalous results. I believe it was a fair test as I only changed two parts (the concentration and volume of Hydrochloric acid) of the experiment and only changed one per test. ...read more.

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