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Investigate the effect of reducing the concentration of Sodium Thiosulphate on the speed of the reaction.

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Alexandra Salters 11HLSC1 Mrs. Seggie Oct/Nov 2002 Chemistry Coursework Introduction: When Hydrochloric acid and sodium Thiosulphate are mixed a chemical reaction occurs which produces a precipitate sulphur. This is cloudy in appearance and eventually enough is produced to obscure a cross on a piece of paper. You can get a measure of how fast the reaction works by timing how long it takes to obscure the cross. Aim of Experiment: I am going to investigate the effect of reducing the concentration of Sodium Thiosulphate on the speed of the reaction. Prediction: I think that as the concentration decreases the reaction will become slower. I think this will because from my scientific knowledge I know that when we decrease the concentration of Sodium Thiosulphate there are fewer particles of Sodium Thiosulphate. Therefore there are fewer chances for the particles to successfully collide with the acid in order for them to react. I also think if I have half the concentration of the Sodium Thiosulphate the time will double. I think this because as I half my concentration the particles will take double the time to react, this will therefore mean half the chance of successful collisions between particles. ...read more.


* I will repeat the experiment 5 times, each time diluting the mixture. * When I have done this I will repeat the experiment again to make it a fair test and also to make my results more accurate. * To make the experiment a fair test I will measure the Sodium Thiosulphate Hydrochloric acid and water accurately. I will also use the same piece of paper with the same cross on it. Results Sodium Thiosulphate Acid Water Time taken for cross to disappear Average 1st Time 2nd Time 25cm3 5cm3 0cm3 30 Secs 26 Secs 29 Secs 20cm3 5cm3 5cm3 32 Secs 31 Secs 31Secs 15cm3 5cm3 10cm3 52 Secs 50 Secs 51 Secs 10cm3 5cm3 15cm3 93 Secs 91 Secs 92 Secs 5cm3 5cm3 20cm3 198 Secs 195 Secs 196 Secs My results prove that my scientific theory is correct. My results show that as a decrease the concentration and dilute my mixture the reaction takes longer. It also shows that when I half my concentrations it takes twice as long to react this is because when we half the concentration we double the time because the reaction takes longer. ...read more.


I would measure my reacts more carefully using either a pupette or burette, as these would measure the volumes more accurately. It can sometimes be difficult to measure the perfect amount due to lack of time or a generous hand. I would also make sure I used the same cross, as I lost mine and had to make another. These were only minor problems and were easily overcome they didn't effect my results thankfully. A final improvement would be to use a colorimeter to measure the cloudiness of the reaction this would give me very accurate results. Other things that I could of investigated in order to improve my knowledge and work. I could see what effect temperature would have on the results within the experiment from my Preliminary work I would have predicted that if I heated the solution the reaction would have been quicker. I could also of changed the concentration of the constant in this case acid this would of caused the experiment to speed up because there would be more chance of successful collision because there would be more particles then could of looked at the difference in the results. Overall I am very pleased with my experiment and my results I have found ways to improve my experiment if I had to ever do it again. ...read more.

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