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How much concentration of sodium thiosulphate (Na2S2O3) affects the rate of reaction when tested with Hydrochloric acid (HCL).

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Background Information Chemical reactions happen at widely different rates. The weathering of buildings and statues caused by acid rain is very slow, but the reactions that take place when a firework explodes are very fast. Most reactions take place at a rate somewhere between the firework explosion, which is almost instant. Finding out how quickly reactions take place and understanding why they happen at the rate they do is very important to the chemist. Speeding up useful reactions and slowing down harmful ones can be important in industrial production processes, and in activities such as preserving buildings or foodstuffs. The use of domestic refrigerators and freezers, as well as cold storage by wholesalers, in transit and in shops, makes modern methods of feeding large populations possible by slowing down the speed at which foods decay. The chemical reactions that take place in the human body happen at extremely slow rates when they are unaided. ...read more.


The rate at which carbon dioxide is evolved can be followed by attaching a gas syringe to a test tube in which the reaction is occurring and noting the volumes at fixed time intervals. By sampling the reaction mixture and the concentration of one of the components of the reaction mixture (either reactants or products) at regular intervals, the concentration of the reaction mixture can be estimated by titration. An example is the acid-catalysed hydrolysis of an ester such as ethyl ethanoate, CH3COOC2H5 + H2O � CH3COOH + C2H5OH. The reaction mixture is titrated at intervals against a standard solution of sodium hydroxide; there is a constant concentration of acid present as catalyst, so as the reaction progresses, more alkali is required due to the formation of ethanoic acid. In some reactions, electrical conductivity can be measured, as this changes as the reaction proceeds. For example, during the alkaline hydrolysis of bromoethane, C2H5Br + OH- � C2H5OH + Br-, the conductivity decreases because the fast-moving hydroxyl (OH�) ...read more.


I will change the Na2S2O3 solution from 0.2ml to 0.4ml, 0.6ml, 0.8ml, and finally 1ml in separate experiments). Using two measuring cylinders pour 0.5ml of HCL into one of the cylinders and the first amount of Na2S2O3 Into the other cylinder. 3. Draw an X symbol onto a clear sheet of paper. 4. Put the flask onto the paper and empty both of the cylinders into the flask and start the stop clock. 5. Repeat this experiment with all of the other concentrations of Na2S2O3 three times. Results: HCL Concentration (ml) Na2S2O3 Concentration (ml) 1st time (seconds) 2nd time (seconds) 3rd time (seconds) Average 0.5 0.2 30 31 32 31 0.5 0.4 23 22 25 23.5 0.5 0.6 10 11 14 12 Conclusion: My prediction was correct. As I added more Na2S2O3 the reaction speeded up and was shorter with the more Na2S2O3 I used. In my first experiment my average time of the X disappearing was 31 seconds and in my second concentration the time was only 23.5 seconds (average) and in my last experiment it the average was only 12 seconds. Harvinder Singh 11GK Harvinder Singh 11GK ...read more.

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