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To find out how the rate of reaction between sodium thiosulphate and hydrochloric acid is affected by changing the concentration.

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Introduction

Chemistry investigation - concentration Aim: To find out how the rate of reaction between sodium thiosulphate and hydrochloric acid is affected by changing the concentration. Prediction: The equation between sodium thiosulphate and hydrochloric acid is: Sodium thiosulphate + hydrochloric acid � sulphur + sodium chloride + sulphur dioxide + water Na2S2o3 (aq) + HCl (aq) � S (s) + NaCl (aq) + SO2 (g) + H2O (aq) We draw a black cross on the back of the test tube. When the cross is completely obscured, the reaction will have finished. The black cross will have disappeared because the build up of Sulphur gas particles will form bonds with the liquid particles, creating a solution. The time taken for this to happen is the measure of the rate of reaction. We must do this several times, and change the concentration of sodium thiosulphate. The rate of reaction is a measure of the change, which happens during a reaction in a single unit of time The factors affecting the rate of reaction are: Temperature: All reactions go faster at a higher temperature. In fact, the rate of reaction doubles by a temperature increase of just 10�C. In this experiment, the particles in the thiosulphate and hydrochloric acid will speed up if the temperature gets slightly warmer. Surface Area: The surface area of a solid means the amount of surface that is exposed to the outside. If you cut up a solid into pieces, the surface area gets larger. There are no solids in this experiment, but if we were to add a potato for example, the higher its surface area, the more exposed it will be to the acids and the quicker the reaction will take place. ...read more.

Middle

If these points are not taken into account, results will be come very inconsistent and I would have to deem the results inaccurate. Safety Precautions: There are a lot of safety issues I must abide by in this experiment also. * I must remember that the substances that we use in this experiment can be very harmful if used the wrong way. * When I do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the test tube during the experiment, one must still be cautious of spills. * I must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. * We should also try our best not to spill any chemicals, as these substances can stain clothing and other upholstery * I must not eat or drink in the lab while dealing with these harmful chemicals, if I handle chemicals without washing my hand afterwards, and then handle food, I could inadvertently swallow some of the acid on my hand, and I might fall ill. * Plasters should cover any open wounds that I may have, as any chemical spillage on the wound can cause me immense pain and possible infection of it. * If any chemical is spilt onto any part of the body, most notably the hands, I must make sure that I clean them afterwards thoroughly as any contact with acid-covered hands to my eyes or my mouth will cause great and extensive injury. ...read more.

Conclusion

I would have also prepared five different test tubes to use, instead of frantically cleaning one each time after use. In the science lab I was using, the sodium thiosulphate and the hydrochloric acid were constantly being spilt, and in some cases, were in contact with each other, this meant that the pair reacted before entering the solution. I would have set them very far apart i.e. one at each end of the classroom. Finally, I would have asked for a white scientist's coat, or something like that to wear, because fibres from my clothes might have contaminated the solution. Though unlikely, and didn't affect my experiment, it could ruin someone else's experiment. Next time, I would also make sure that the artificial light maintains the same intensity, as the higher the intensity, the hotter the air around it become. Since temperature affects the rate of reaction, it could affect my experiment. I will also make sure that my eyes are the same distance from the test tube and the black cross, because the closer you are to the black cross, the better you can see it. For each experiment, if I keep changing the distance between the black cross, and myself the times aren't going to be consistent. I will stay at a constant distance so that my observations of the black cross are constant. For further work, I could have made the solution more concentrated. For instance I could have the very concentrated solution, where there is no water in the solution. In the other extreme, I could make the solution totally diluted, but I think that could have tested my patience. I think that I could have diluted the mixture next, by adding more water each time than hydrochloric acid. This will test anyone's prediction and could lead to some interesting results. ...read more.

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