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Investigate how changing the concentration of sodium Thiosulphate affects the rate of reaction.

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Chemistry Coursework John McHugh Investigation Task- Investigate how changing the concentration of sodium Thiosulphate affects the rate of reaction. Method For this experiment I am going to use a black cross and place it at the base of the flask. Then I will add both Hydrochloric Acid (HCL) and Sodium Thiosulphate to the conical flask, and mix. Then I will start the stopwatch. There will also be a thermometer to check temperature at the start and finish of the reaction. After starting the stopwatch I will look down through the solution at the cross. As the reaction takes place the solution will become cloudier as sulphur is produced. When I can no longer see the cross I will stop the timer. I would repeat this test and reduce the amount of Sodium thiosulphate and increase the volume of water. ( vary the concentration) I will need � 200cm3 of Hydrochloric Acid * 275cm3 of Sodium Thiosulphate * 275cm3 of water * 3 Beakers * Measuring Cylinders * Conical Flask * Stopwatch * Thermometer * Black cross ...read more.


In a weaker solution water particles get in the way of the reaction therefore slowing down the reaction. fig 1b . There are more sodium Thiosulphate and Hydrochloric acid In 1 ml of the solution in a high concentrate so more collisions occur per second, giving a faster reaction. Therefore there is a speeder reaction. When there are more water particles in 1 ml of the solution, there is less space for Sodium Thiosulphate so less collisions can take place in a second. Therefore you get a slower reaction. If I double the amount of sodium thiosulphate There will be twice as many particles of sodium thiosulphate per 1ml and therefore there will be twice as many reactions per second so the reaction time will be halved. If I half the amount of sodium thiosulphate There will be 1/2 as many particles of sodium thiosulphate per 1ml therefore there will be half as many collisions per second which would result in the reaction time being doubled. ...read more.


In a high concentrate there are far fewer water particles to get in the way of the reaction between the Sodium Thiosulphate and Hydrochloric acid (Na2 s2 o3 2HCl SO2 S NaOH H2O) so more sulphur can be produced In a second so the cross can be covered up quicker and therefore it has a faster reaction time. Evaluation I thought that this experiment went relatively well. I think I have conclusive evidence to show how concentration affects reaction rates. My graphs had no anomalous results and I have a nice best-fit line. In this experiment there could be a lot of human error e.g. looking through a solution and knowing when the solution is fully clouded could differ for each experiment. Measuring of solutions might not be very accurate, the time delay between the solution going cloudy and stopping the stopwatch could differ from differ. I would use two different solutions such as using magnesium ribbon and different concentrates of sulphuric acid just to check if it's not only that reaction that speeds up when there is a higher concentration. ...read more.

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