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# How does the concentration of sodium thiosulphate solution affect the rate of its reaction with hydrochloric acid?

Extracts from this document...

Introduction

Helen Bewick 10C How does the concentration of sodium thiosulphate solution affect the rate of its reaction with hydrochloric acid? During this investigation I hope to find out if the concentration of sodium thiosulphate solution affects the rate of its reaction with hydrochloric acid. I will do this by reacting hydrochloric acid and different dilutions of sodium thiosulphate solution and working out their rates of reaction. Prediction The higher the concentration of sodium thiosulphate solution the faster the rate of it's reaction will be and the less amount of time it will take to react with hydrochloric acid. The collision theory states that in a higher concentration there is a larger amount of particles in a given volume so there will be a more likely chance of successful collisions and the rate of reaction will increase. Lower concentration Higher concentration Key -Sodium thiosulphate molecule - H20 molecule I also predict that as the concentration doubles the rate of reaction will also double. This is because there will be double the amount of particles in a given volume so there will be double the amount of successful collisions and therefore the rate of reaction should double. Predicted graphs- I predict my graphs will look like this. Preliminary plan The aim of my preliminary work is to test my method and to decide the number and strength of sodium thiosulphate solution I will use in my investigation. I will need a wide range of results. Factors to control The independent variable that I will not control is: * The rate of reaction, The variables that I will keep the same are: * Temperature- I will keep the temperature the same by checking the temperature with a thermometer and ensuring it stays roughly the same. I need to keep the temperature the same because the collision theory states that an increase of temperature leads to an increase in rate of reaction because as the temperature increases the average kinetic speed of the particles increases, so more pairs of particles will have more energy between them and so there will be more successful collisions. ...read more.

Middle

During the reactions I will record the time taken in seconds for each concentration to react. I will find the rate of reaction using the equation 1/time taken for the cross to disappear. I will find the rate of reaction so that I can draw a graph and compare the concentration of sodium thiosulphate solution against rate of reaction. When I am measuring all the solutions I will make sure the measuring cylinder is on a flat level surface and measure to the bottom of the meniscus. I will use 10cm3 measuring cylinder when measuring 10cm3 and below and I will use a 50cm3 measuring cylinder when measuring between 10cm3 and 50cm3. I will do this to make sure that the experiment is a fair test and I will use equal amounts of reactants in each experiment. 1. First I will set up the apparatus as shown above. I will note down the temperature. 2. I will be investigating 8 different concentrations. The concentrations I will use are 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, 0.03 and 0.02 mol/dm3. The first concentration of sodium thiosulphate solution that I will be using is 0.09 mol/dm3. I will need 45cm3 of sodium thiosulphate and 5cm3 of distilled water. I will measure the sodium thiosulphate solution, distilled water and hydrochloric acid into different measuring cylinders. 3. Next I will place a conical flask onto a piece of paper with a cross on it. 4. Then I will need to pour the reactants into the conical flask as I simultaneously start the stopwatch. At the beginning of the reaction the liquid should be clear and the cross should be seen easily. 5. I will time the experiment until the reactants have gone opaque. Sulphur is formed in the reaction causing the reactants to become more and more cloudy and I will no longer be able to see the cross. ...read more.

Conclusion

If I did my investigation again I could do several things to make it more accurate: * I did my investigation over 2 days and I used different batches of hydrochloric acid and sodium thiosulphate solution. They could have been a slightly different concentration, which would have affected the rate of reaction. I would make sure I used the same batch. * I used different conical flasks over the two days which could have been of a different thickness of glass and would have made it more difficult to see the cross. If I re did the experiment I could make sure I used identical conical flasks. * After I had finished experimenting with one concentration I just washed out the conical flask and dried it with paper towels and re used it. This sometimes left residue on the inside of the conical flask which was difficult to clean because of the narrow neck. This residue could have affected my results because it changed the concentration of the reactants. I could try to clean it better or use clean conical flasks for each concentration. * I would try and measure the volume of the hydrochloric acid, sodium thiosulphate solution and distilled water more accurately by using a burette, metric flask and pipette filler. * During my investigation it was very difficult to distinguish between the hydrochloric acid, sodium thiosulphate solution and distilled water because they are all clear liquids. If I repeat the investigation I could try dying the liquids different colours but before I did this I would have to make sure it didn't affect the rate of reaction or time taken for the cross to disappear. * For safety reasons if I repeated the experiment I could collect the sulphur dioxide that is produced in a boiling tube through a delivery tube. This would prevent any gas being released. I think my evidence is still quite reliable. Most of my repeat readings are similar. I think I have enough evidence to make a firm conclusion that my prediction was correct. ...read more.

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