Rates of reaction:- sodium thiosulphate + hydrochloric acid

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Rates of reaction:- sodium thiosulphate + hydrochloric acid


We must produce a piece of coursework investigating the rates of reaction, and the effect that changing one particular variable has on the reaction time. The rate of reaction is the time it takes one or more of the reactants to react or the time it takes to produce a new product from a chemical reaction. To work out the reaction time we use the formula.

                       1 divided by time taken for reaction

 There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles:

  1. temperature of solution,
  2. concentration of solution,
  3. pressure of gases in reaction,
  4. surface area of reactants,  
  5. Catalysts.

 For my preliminary experiments I have chosen to investigate the effect temperature and concentration have on a reaction. I have chosen to investigate these reactants because the are the most practical for the lab and equipment that I have available to use also it would take to much time to prepare a solid in powdered and unpowdered form, and it is difficult to get accurate readings due to the inevitabilities of human errors, and as gas is mostly colourless it is difficult to gauge a reaction changing the pressure, and if a substance is added to give the gas colour, it may influence the outcome of the experiment. Similarly the use of a catalyst complicates things, and if used incorrectly could alter the outcome of the experiment.

My preliminary experiments showed me that it would me more practical and time saving if I just altered the temperature of the solution as changing the concentration of the solution was very time consuming.  However the preliminary experiments also helped me to choose a suitable strength of solution.


   To see the effects of a change in temperature on the rate of a reaction. The reaction that will be used is:

  Sodium  Thiosulphate + Hydrochloric Acid.
        Na2S2O3 (aq)     +         2HCl (aq) .

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As I decided after my preliminary experiments I will only carry out one experiment, temperature change whilst all other variables stay constant. As both, sodium thiosulphate and hydrochloric acid are soluble in water it means that I would be able to alter the concentration of either of them. However I have chosen to vary the sodium thiosulphate as it is available in larger amounts.  To alter the temperature of the solution a water bath will be used to heat up the acid, thiosulphate and water to the necessary temperature.

I decided on my range temperatures and the concentration that I ...

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