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# The effect of concentration on the rate of reaction

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Introduction

The effect of concentration on the rate of reaction Prediction I think that when the concentration of sodium thiosulphate is high then the cross will disappear more quickly. If the concentration of sodium thiosulphate is low then the cross will take longer to disappear. This is because there are more sodium thiosulphate particles. These, when mixed with the water particles, form a 'foggy' solution. The more sodium thiosulphate particles there are the more chance there is that they will collide with the water particles. When they collide then the reaction above takes place and the water goes foggy. This means that the more collisions that take place the quicker the solution turns from transparent to translucent. There are several variables: some that we shall endeavour to keep the same others that we shall be experimenting with. 1) The amount of water. 2) The amount of hydrochloric acid. 3) The amount of sodium thiosulphate. 4) The total amount of solution. 5) The temperature of the components in points 1), 2) and 3). This is what I plan to do to the above variables throughout the experiment. I shall change the amount of water and sodium thiosulphate as explained in the method below. I shall keep the hydrochloric acid amount constant at 5 cubic cm. The total amount shall always add up to 55 cubic cm. ...read more.

Middle

This is because there were more sodium thiosulphate atoms to collide with the water atoms. This means that the reaction took place faster. The graph which shows sodium thiosulphate against time is a downward sloping curve. This shows that the two variables are not directly proportional. It also shows that the less sodium thiosulphate there was the longer the reaction took. There appears to be just two small anomalies at 20cm3 and 25 cm3. These do still, however follow the trend and should not cause me to doubt the accuracies of my experiment. The graph to show the rate of reaction against the amount of sodium thiosulphate is a straight line going through the origin. This shows that the two variables are directly proportional. This is because if there is twice as much sodium thiosulphate their will be twice as many atoms. This means that the chance of a collision between the sodium thiosulphate atoms and the water atoms double. This means that the reaction will go twice as quickly. This explains why there is a direct relationship between the two. My original prediction was that when the concentration of sodium thiosulphate is high then the cross will disappear more quickly. If the concentration of sodium thiosulphate is low then the cross will take longer to disappear. My results support my prediction, as the rate of reaction was faster when there was more sodium thiosulphate. ...read more.

Conclusion

There were no results that were so anomalous that I needed to redo the test for that reading. My results always showed a clear trend and so I feel that my results were accurate. I could have improved the accuracy however by using a light sensitive detector. I would place this underneath a tripod and place the beaker on the tripod. I would have carried out the experiment as above. The light sensitive detector would have enabled me to know exactly when the light could no longer penetrate the solution. This would have given me more accurate results. Another way of extending the experiment and thereby improving the accuracy of the experiment would be to take more readings. This would ensure greater accuracy. It would especially help when drawing the line of best fit, as there would be more points upon which to base it on. Ideally every single variant concentration of water and sodium thiosulphate would be used between 0 and 50. I could also carry out another experiment to see how the concentration affects the rate of reaction. I could place some magnesium ribbon in pure hydrochloric acid. I could then put the magnesium in varying concentrations of HCl by diluting it with water. I could then time how long it took the magnesium ribbon to disappear. I would do each experiment twice to improve accuracy. I would expect to find that the higher the concentration of hydrochloric acid the faster the magnesium ribbon would disappear. ...read more.

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