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Investigating The Rate of Reaction Between Hydrochloric Acid and Sodium Thiosulphate

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Investigating The Rate of Reaction Between Hydrochloric Acid and Sodium Thiosulphate Equipment � 2 Measuring cylinders � Conical flask � Beaker � Stopwatch � Paper with cross marked on it � Sodium Thiosulphate solution � Hydrochloric Acid � Water Diagram Variables > Temperature > Concentration > Surface Area > Catalysts The variable I will change is concentration. I chose this reaction variable because it has a definite end point (when the cross disappears on the paper). You cannot calculate the surface area as we are not using solids and no catalysts are used either. To make this experiment a fair test I will only vary one thing - the concentration of the Sodium Thiosulphate solution. I will conduct all the tests at room temperature because temperature has an effect on the rate of the reaction. The measures of Hydrochloric acid will all be the same (10cm�). The person timing the experiment will look for the disappearance of the cross, otherwise there would be a time lapse between seeing the cross disappear and telling the other person to stop the clock and then eventually stopping the clock. ...read more.


* Taking care when using glassware to prevent injury. Plan I am going to pour 50cm of Sodium Thiosulphate or Na S O into 10cm of Hydrochloric Acid in a conical flask. I will then test 40cm of Sodium Thiosulphate with 10cm of water, 30cm of Sodium Thiosulphate with 20cm of water and so on until there is only 10cm of Sodium Thiosulphate with 40cm of water, as shown in the table below. The flask will be placed on a piece of paper with a cross drawn on it. I will start the stopwatch when I add the acid to the Na S O. I will stop the stopwatch when the solution is cloudy enough to prevent me seeing the cross. I will repeat this procedure with the measurements in the table below. Then to gain an average I will repeat all the tests three times. Concentration (in Molar) Thiosulphate (cm�) Water (cm�) 0.15M 50cm� 0cm� 0.12M 40cm� 10cm� 0.09M 30cm� 20cm� 0.06M 20cm� 30cm� 0.03M 10cm� 40cm� Results I have recorded my results in tables and then worked out the averages afterwards to gain a more accurate result. ...read more.


I believe I was correct and a secondary source states that the reaction time will be faster with a more concentrated solution because,' the more molecules there are, the frequency of successful collisions is greater and therefore the reaction rate is speeded up. Evaluation My experiment went according to plan but there were flaws in it. For example I could have done more tests to gain a more reliable average. I think there is also a human error factor involved when you are measuring liquids and looking for an end point in the reaction. Although the reaction I chose had a fairly definite end point it was still hard to tell whether the whole cross had disappeared or not. Instead of using a cross a light beam could be used and when the beam goes out that is the end point. There were two results that were not really anomalies as they still followed the pattern but were slightly different to the other results of the other tests. This could be human error, which is the reason for doing more tests. ?? ?? ?? ?? Katy Gardiner 10S4 ...read more.

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