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Effect of concentration on rate of a reaction.

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Year 10 AT1 Factors effecting the rate of a reaction Aim: Effect of concentration on rate of a reaction Reaction: Sodium Thiosulphate and dilute hydrochloric acid Apparatus: � Sodium Thiosulphate � hydrochloric acid Water � Conical flask � measuring cylinder � stop watch � Card with a black cross on Method: � Place your conical flask over the black cross. � Add 5 cm cubed of hydrochloric acid, this acts as a constant, and gets the reaction going. � Measure out 50 cm cubed of sodium thiosulphate and pour it into the conical flask with the hydrochloirc acid. Get ready with the stop watch and time to see how long it takes for the solution to become cloudy and for the black cross to disappear. � Now do the experiment again, but this time lowering the concentration of the sodium thiosulphate solution, and adding 10 cm cubed of water. � Continue to increase the water concentration and lower the sodium thiosulphate solution, until the cross disappears. � As a control for the experiment, add 50 cm cubed of water to the hydrochloric acid, without any sodium thiosulphate solution. ...read more.


� The volume of the hydrochloric acid. If this changed in each experiment, then each would react at different rates, causing different times for the reactions to occur, so we kept the volume of the hydrochloric acid the same. � Once a reaction has occurred, then the conical flask where the reaction took place should be washed out thoroughly in order to prevent the next reaction from being contaminated. This would cause different rates of reaction to occur, causing an unfair test. Predictions: In our hypothesis above we have seen how the rate of a reaction is effected. From the hypothesis I predict that: � The more sodium thiosulphate that is added, the quicker the reaction will be. I think this because as we have seen above, the more sodium thiosulphate molecules there are, and less water molecules, there will be more collisions with the hydrochloric acid molecules which means more a quicker reaction. � Therefore we can say that if there are more water molecules than sodium thiosulphate molecules then it will be a slower reaction. � When we mix hydrochloric acid with just water, I predict that no reaction will take place. ...read more.


The main problem being, that it is difficult to decide exactly when the black 'X', has totally disappeared. Because of this my results could be slightly off by a few seconds on each. The other problem is that we had to rinse out the conical flask we were using, and re-use it throughout the experiment. Therefore, the conical flask may be contaminated at some point and effect the results slightly. To overcome these problems, and to improve upon the experiment, we could change some of the ways of doing it. For example, instead of using a black 'X' to place under the conical flask, we could use a light sensor with timer. This would only work in a blacked out room. But it would give us even more accurate results. The light sensor would be placed under the conical flask in place of the black 'X'. Once the reaction has started, the light will gradually fade, and once no light can be sensed, the timer will stop. Instead of re-using the conical flask, we could have a separate, clean conical flask for each reaction that you do. This would insure that none of the flasks are contaminated and a fairer test. ...read more.

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