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When Sodium Thiosulphate and dilute Hydrochloric acid react they produce a cloudy precipitate. The chemicals are both clear solutions and will react together to form a yellow precipitate of Sulphur.

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Introduction

Theory When Sodium Thiosulphate and dilute Hydrochloric acid react they produce a cloudy precipitate. The chemicals are both clear solutions and will react together to form a yellow precipitate of Sulphur. The equation for this is; Na2S2O3 + 2HCl 2NaCl + SO2 + S + H2O As the solution turns cloudy we can observe the rate of reaction by placing a red cross under the beaker and seeing how long it takes for it to disappear. There are various factors that could affect this experiment, this are, time, concentration and temperature. I don't think surface area will be a factor as both chemicals are in liquid form. In my experiment I will be changing the concentration. I think that as the concentration of the Sodium Thiosulphate gets greater the time taken for the cross to disappear will become shorter. This is because in order to react with each other the two particles must be in direct contact. With the lower concentrations there will be less particles and they will be spread around more and be further apart meaning that they will meet less often and reactions will happen less. ...read more.

Middle

* Keep repeating, adding 10cm3 less Sodium Thiosulphate and 10cm3 more water each time. When all this is done I will repeat the entire experiment again so that my results are more reliable. Results Set 1 Volume of 0.15mol/dm Sodium Thiosulphate solution (cm�) Volume of Water (cm�) Concentration of Sodium Thiosulphate solution (mol/dm) Time for cross to be obscured (seconds) Rate of Reaction 1/time (1/seconds) 50 0 0.15 25 0.040 40 10 0.12 31 0.032 30 20 0.09 41 0.024 20 30 0.06 58 0.017 10 40 0.03 79 0.013 Set 2 Volume of 0.15mol/dm Sodium Thiosulphate solution (cm�) Volume of Water (cm�) Concentration of Sodium Thiosulphate solution (mol/dm) Time for cross to be obscured (seconds) Rate of Reaction 1/time (1/seconds) 50 0 0.15 24 0.042 40 10 0.12 29 0.034 30 20 0.09 38 0.026 20 30 0.06 75 0.013 10 40 0.03 73 0.014 Average Set Volume of 0.15mol/dm Sodium Thiosulphate solution (cm�) Volume of Water (cm�) Concentration of Sodium Thiosulphate solution (mol/dm) Time for cross to be obscured (seconds) ...read more.

Conclusion

This contrasts with all the other results and also my predictions. It is also noticeable in the graph where it is shown as the out of place dip in the line. This could have been caused by a number of things such as: * Measuring - Measuring of chemicals in liquid form is difficult to do accurately because of the movement in the liquid and the accuracy of the measuring cylinder. * The person watching could have been mistaken as to when the cross disappeared. * If the same person watching the reaction was operating the stop-watch then errors could of occurred in their coordination. These errors could be removed by: * Using electrical measuring apparatus or failing that using a burette as these are still more accurate than a measuring cylinder. * Using a light sensor to detect when the cross is no longer visible. The experiment would be connected to a light sensor and timer and the sensor would detect when there was no light coming through the solution. Although this would increase accuracy dramatically it would also involve the use of expensive equipment that is not always available. Other than that one anomalous result I think that the experiment is fairly accurate. ...read more.

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