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Investigation into how the concentration of Sodium thiosulphate affects the rate of reaction.

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Introduction

Investigation into how the concentration of Sodium thiosulphate affects the rate of reaction In this investigation I am going to find out how the concentration of Sodium thiosulphate affects the rate of reaction when reacting with hydrochloric acid. In the experiment there are many factors that could change the reaction rate, these are; * Temperature as the higher the temperature, the faster the particles move, increasing the chance of a successful collision * Stirring the solution as it gives the particles more energy to collide with. * Concentration of the Hydrochloric acid / Sodium thiosulphate as the more particles there are in the solution, there is a higher chance of a successful collision. * The volume of the Hydrochloric acid / Sodium thiosulphate as this again increases the chance of a successful collision as there are more particles to be collided with. In this investigation I have chosen to change the concentration of the Sodium thiosulphate as it is an easy factor to change. The reaction that will be used is: In this investigation, I predict that as the concentration of the Sodium thiosulphate increased, the time taken for the reaction will decrease. I predict this because as the concentration of the Sodium thiosulphate increases there are more particles for the hydrochloric acid to collide with. The frequency of collisions increases, making the chance of a successful collision greater. ...read more.

Middle

To make the readings as accurate as possible I am going to use the teat pipettes to get the Sodium thiosulphate and hydrochloric acid as accurate to the measurements as possible. The same safety precautions are going to be used as in the preliminary work. To start the experiment take 50cm� Sodium thiosulphate and add to the conical flask. Add 10cm� hydrochloric acid and pour into the conical flask and stir once. Start timing the experiment and watch the solution to turn colour until the X underneath the conical flask and stop the stopwatch. I then repeated the same method using the ratio sodium thiosulphate : water for: 40:10 30:20 20:30 10:40 The results for the investigation are below. Vol. of Thiosulphate (cm�) Vol of water (cm�) Time taken for X to disappear 1 2 3 Average 1/t 50 0 21.68 21.5 - 21.59 0.046 40 10 24.5 23.78 2.63 23.71 0.042 30 20 33.28 32.03 - 32.66 0.031 20 30 45.59 49.97 50.5 47.78 0.021 10 40 140.62 135.4 139.22 139.92 0.0071 Looking at my results, I can see that my prediction was right and there is a clear pattern seen between the time taken and the ratio between the sodium thiosulphate. As the sodium thiosulphate decreases in concentration the time taken increases. My quantitative prediction was also true as the time taken also doubles when the concentration halves. For example, the 20:30 and the 40:10 double from 0.021 to 0.042. ...read more.

Conclusion

The hardest was keeping the temperature the same as it was carried out in room temperature. Also, stopping the stopwatch at the exact time is hard to do as there is a reaction time before you press the button. Some of the results had to be repeated a 3rd time. This could be because of many different factors such as timing incorrectly, spilling acid or a slight increase/decrease of acid. These factors could also be applicable to the anomalous results in my experiment. In my opinion using the average of 2 results only gives a rough idea of the time taken. To make the results more reliable, I think 5 readings would be more accurate and up to 10 concentration. To make the timing as accurate as possible I would use a light probe to measure the amount of brightness passing through the solution. When the light passing through gets dark enough, that is when the timing of the experiment stops. To keep it a fair test we would stop when an exact amount of brightness is lost through the solution. To further advance the investigation I would then do another experiment changing a different factor such as increasing/decreasing the temperature. If the temperature is increased the rate of reaction would also increase as the particles would have more energy to collide with each other, in turn increasing the successful collision rate. ?? ?? ?? ?? Mathew Howell ...read more.

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