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Investigate the effect of concentration on the rate of a reaction.

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Disappearing cross experiment Chemistry Coursework: Rate of Reaction Planning Aim: To investigate the effect of concentration on the rate of a reaction. Prediction: 'I predict that as the concentration of the solution decreases the rate of reaction will decrease too.' Therefore the length of time for the cross to disappear will increase as the concentration is decreases. I think this because more molecules are present in a higher concentration and therefore there is more chance of them colliding with each other. The more particles there are the more chance there is of having more energy than the activation energy. It means the solution will be very crowded and it doesn't increase the speed at which they collide only changing the temperature would give the energy to do this. There are many factors that also very the rate of reaction. The surface area because the more the area there is on the surface the more chance the particles have of colliding with a solid such as the beaker. A catalyst as well because it lowers the activation energy that is required. And finally the temperature because if it were to increase between the tests the speed of the molecules will increase causing more of a chance that the particles will collide. This will make more energy from the activation energy. The energy needed to start a reaction is called activation energy; however the activation isn't effected by the reaction in this experiment. ...read more.


There should be 3 test for each different concentration used. Water is used to dilute the solution so that the concentration decreases, but the volume is always the same in every test. From this experiment the conclusion was that as the concentration of the acid decreases, the time taken to collect 50cm of Carbon Dioxide from the reaction, increases. This means the rate of reaction decreases as the concentration is less. This is because there are more particles to collide at higher concentrations so these are more successful collisions. Another experiment carried out was the 'effect of temperature on the rate of reaction'. This is when 50cm Sodium Thiosulphate is poured into a conical flask which is placed above a clear cross drawn on a piece of paper. 5cm of Hydrochloric Acid is added after the Thiosulphate has been heated to a sensible temperature. The time taken for the cross to disappear is then recorded. This test should be carried out 3 times and then the temperature should be changed so that the molecules are moving at different rates. In conclusion to this experiment, as the temperature of the liquid increases the time taken for the reaction to take place decreases. This means the rate of reaction increases and becomes faster. This is because the particles are now colliding at a faster speed on temperature increasing in the liquid makes the particles vibrate vigorously. ...read more.


The results were fairly accurate as they were to 2 decimal places. If they were much more accurate it would become fairly complicated as the unit was seconds. There was one anomaly in this experiment being this result: 10 146.28 153.34 186.93 anomaly 149.81 0.0067 This could have been for many reasons. The main one being that the measurements for this test weren't as accurate as the other 2 taken and therefore the result has become quite different to the others. The measurement could have been wrong for any of the solutions, that is the water, Hydrochloric Acid and the Sodium Thiosulphate. This experiment could have been improved through many things. Computerised equipment could have been used to improve the accuracy of the measurements as it is an awesome lot more accurate than the naked eye. The solutions could have been timed more often, so instead of 3 times maybe 10 and that way the average would be a lot more accurate. Another experiment that could be carried out to measure the rate of reaction would be the 'volume of gas given off.' For this, a conical flask needs to contain a sensible amount of dilute hydrochloric acid. There should be a bung in the top containing a tube which leads to a syringe. Marble chips should be put into the flask, and the bung put straight back in again. Collect the gas given off from the marble chips in the syringe and when 100cm has been collected stop timing how long it took. This should be carried out a sufficient number of times to get an accurate reading. Justine Gray ...read more.

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