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The Effect of Concentration on the Reaction of Sodium Thiosulphate with acid

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The Effect of Concentration on the Reaction of Sodium Thiosulphate with acid Harry Weeks This is an investigation to find the effect that altered concentration has on the rate of a reaction. The reaction in question here will be that of sodium thiosulphate with hydrochloric acid. The equation for this reaction is thus: Na2S2O3 (aq) + 2HCl (aq) ==> 2NaCl (aq) + S (s) + H2SO3 (aq) Sodium Thiosulphate + Hydrochloric Acid --> Sodium Chloride + Sulphur + Sulphuric Acid This reaction begins as a colourless solution of sodium thiosulphate and hydrochloric acid, but gradually turns cloudy and yellow with the presence of a sulphur precipitate. This precipitate is what we aim to exploit in order to show what effect concentration has on a reaction. Apparatus: Conical Flask Stop Watch Black Cross Measuring Cylinder x2 Method: The two reactants are mixed in a conical flask. The concentration of the hydrochloric acid is kept constant at 1Mdm-3 (bench HCl) and 10cm3 is added each time giving 0.01M in each experiment. The concentration of sodium thiosulphate is altered each time but its volume will always be 30cm3. ...read more.


* The line of best fit for the 1/t against volume graph will cross the x-axis just before the origin. - This is because at small concentrations, there will not be enough molecules of sodium thiosulphate to react and cover the black cross. So however long the reaction is left for, it will never complete the experiment. Results: Volume of Na2S32O3 / cm Volume of H2O / cm Volume of HCl / cm time/s 30 0 10 59 25 5 10 70 20 10 10 89 15 15 10 129 10 20 10 180 5 25 10 NO REACTION Preliminary work results Volume of Na2S2O3 / cm-3 Volume of H20 / cm-3 Volume of HCl / cm-3 Time / s Ave. time / s 1/time / s-1 30 0 10 61 58 59 59.33 0.0169 25 5 10 72 78 75 75.00 0.0133 20 10 10 92 92 96 93.33 0.0107 15 15 10 126 131 147 134.67 0.0074 10 20 10 170 175 179 174.67 0.0057 5 25 10 NO REACTION Experimental results based on volume of substances Moles of Na2S2O3 Moles of HCl Time / s Ave. ...read more.


Extensions: The experiment could be further expanded to provide more conclusive or different evidence to support other theories. The experiment could be altered to analyse the effect of other variables on reaction rate. Heat, light, catalysis and surface area could all be accommodated in extensions of this experiment by making them the controlled variables and keeping all others fair. Making sodium thiosulphate the control and altering the concentration of hydrochloric acid could further test concentration's effect on rate of reaction. This would further prove that concentration has an effect on reaction rate and disprove that this particular phenomenon was not particular to sodium thiosulphate, unlike as that would be. Making the experiment more precise could be done in a number of ways in order to improve quality and reliability of the evidence. The equipment used could be more precise in measurement in order to make quantities perfectly fair. And cleaning the apparatus could be done more thoroughly to prevent contamination. In a perfectly fair analysis of concentration, all other variables would be kept perfectly fair. Therefore heat could be monitored with a thermometer to prevent any day to day heat differences, however small. ?? ?? ?? ?? 1 02/05/07 Harry Weeks ...read more.

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