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Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate.

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Katherine Allen Rate of Reaction between Hydrochloric Acid and Sodium Thiosulphate Aim The aim of this investigation is to find out how the concentration of a solution affects the rate of reaction. I am going to investigate how the concentration of sodium thiosulphate affects the time it takes to react with hydrochloric acid. Introduction When hydrochloric acid and sodium thiosulphate solution react, one product of the reaction is sulphur. The sulphur is produced and appears slowly, eventually resulting in the whole mixture becoming opaque. The word equation for this reaction is: sodium thiosulphate + hydrochloric acid --> sodium chloride + sulphur dioxide + sulphur + water The chemical equation is: Na2S2O3 + 2HCl --> 2NaCl + SO2 + S + H2O There are several factors affecting the rate of reaction. These include the surface area, the temperature, the concentration and catalysts. Surface area The larger the surface area, the more collisions can occur. The reaction is therefore faster. This is not a factor that I need to worry about, considering it is liquids that I will be reacting. Temperature In most reactions, bonds in reactant molecules must first be broken before bond in product molecules can form. The minimum energy required to break the bonds is called the activation energy. ...read more.


The same experiment will be carried out, each time increasing the amount of sodium thiosulphate by 5cm� and decreasing the amount of water by 5cm�. This will continue until there is no water added, just 40cm� of sodium thiosulphate. A thermometer will be kept next to the apparatus and checked regularly in order to ensure no rise or fall has occurred. Safety Throughout the investigation safety goggles will be worn to protect eyes, and care will be taken when handling the hydrochloric acid. Preliminary Work Before the investigation is carried out, preliminary work was done. Experiments were carried out with the highest proposed concentration of sodium thiosulphate and the lowest proposed concentration, in order to ensure that the fastest time would not be too fast and the slowest time would not be too slow. It the reaction occurred too quickly, it would be hard to take an accurate reading from the stopwatch but if it took too long a limited amount of experiment could be conducted within the time allowed. Preliminary Results Acid (cm�) Sodium Thiosulphate (cm�) Water (cm�) Time (secs) 10 5 35 300 10 40 0 28 From my preliminary results I can see that my proposed concentration boundaries will be suitable to time. The preliminary work has also highlight the importance of measuring the liquid out accurately and starting and stopping the stopwatch at exactly the right moment. ...read more.


This is an experiment that relies heavily on human judgement. The exact moment that the liquid in the beaker became opaque may not have been entirely accurate, considering it was judged only by the human eye. Starting and stopping the stopwatch at the right moment may have also been an area of error, although it was done to the best of our ability. 2 results for each experiment are not really enough to ensure they are completely accurate. In a future experiment I would take 3 or perhaps four in order to check for anomalous results. There are many different experiments I could do in order to investigate the rate of reaction between sodium thiosulphate and hydrochloric acid further. I could experiment using even less sodium thiosulphate to see whether or not there is a point whereby my conclusion are no longer true. Alternatively, I could change the variable and investigate how temperature affects the rate of reaction. I would conduct these experiments by measuring out 20cm� of sodium thiosulphate and adding 10cm� of hydrochloric acid. I would then time how long it takes for the cross to disappear. Keeping these volumes the same in every experiment, I would heat the sodium thiosulphate by 10� then add the acid. I would keep heating it by 10� until it reached 70�, each time, timing how long the cross took to disappear and recording the results. ...read more.

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