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The rate of reactions and what affects them - hydrochloric acid and sodium thiosulphate.

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January 2001 *Aim: Investigating the rate of reactions and what affects them. In my case I am going to look at hydrochloric acid and sodium thiosulphate. I am going to investigate how the concentration of hydrochloric acid will affect the reaction. *Background Information: In the investigation I am going to do I am looking at the rate of reactions. In Microsoft Encarta it is defined as the "amount of a substance that takes part in a chemical reaction". Factors can change reaction rates. If substance that are wanted for reaction are heated, the rate of reaction usually rises as well, this also works the other way, if reacting substances are cooled the reaction will slow down. This is due to the fact that in order for a reaction to take part the particles in the substance must collide with each other. This is called the colliding theory. When the substance is heated it gives the particles more energy to move around and so increases the chance of a collision. Also when the particles are moving faster and collide they are more likely to react, rather than just to bounce off each other. When a substance is cooled it has to opposite effect due to the fact that the particles in the substances do not have a lot of energy causing the to move around slower. This then causes fewer collisions and a slower reaction. ...read more.


The volume of the sodium thiosulphate will be kept the same through out the whole experiment, I have decided to keep the volume at 20cm3. I have to change the concentration of the hydrochloric acid by adding distilled water to it each time, but I will always make sure that the total volume of them together will also be 20cm3. *The equipment- I will be using all the equipment listed underneath to test the variable of concentration. 1 * Conical flask 0 - 250 cm3 2 * Measuring cylinder 0 - 25 cm3 2 * Measuring cylinder 0 - 10 cm3 3 * beaker 0 - 250 cm3 White paper Black marker pen Distilled water Stop clock Sodium thiosulphate 0.2 molar Hydrochloric acid 2 molar Pipette *Method I am going to test eight different concentrations for hydrochloric acid. I shall use distilled water to dilute the hydrochloric acid for different concentrations. The hydrochloric acid will be added to the sodium thiosulphate, and together they will react forming a cloudy solution. As these react it will form sulphur, and the more sulphur formed the cloudier the solution will get. The Sodium thiosulphate is going to be a constant variable that I will keep the same through out all of the experiments. I will use 20cm3 of sodium thiosulphate in each experiment I do. ...read more.


taken for cross to disappear /s 2nd attempt Time taken for cross to disappear /s 2.0 20 0 20 43 44 1.6 16 4 20 46 47 1.2 12 8 20 49 52 0.8 8 12 20 51 55 0.6 6 14 20 70 65 0.4 4 16 20 75 67 0.2 2 18 20 96 95 0.0 0 20 20 Doesn't Disappear Doesn't disappear I was now able to find the average of the two sets of results I did to find a more precise reading for the time taken for the cross to disappear for each concentration I tested. Concentration / M Average of time taken for cross to disappear in experiments 1 and 2 /s 2.0 43.5 1.6 46.5 1.2 50.5 0.8 53.0 0.6 67.5 0.4 71.0 0.2 95.5 0.0 Doesn't disappear The results that I have collected do not have any obvious anomalous results but from the line graph I drew I can see the results do not go up in a nice smooth steady line, this is because my results are not completely accurate. I would be almost impossible to get total exact results but to improve mine I could repeat the experiment another two times and then find the average of the four sets of results. I could also increase the amount of concentration changes of hydrochloric acid I do. This will give me a wider range of results. ...read more.

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