Investigating the rate of reaction between sodium thiosulphate and hydrochloric acid Background Sodium thiosulphate and hydrochloric acid react to produce sulphur. Na2S2O3 (aq) + 2HCl (aq) SO2(aq) + S(s) + H2O(l) + 2NaCl (aq)
The sulphur will be deposited in the solution and causes the solution to become opaque. Practical Techniques You will need to find out how to make accurate solutions.
Where to start One way of measuring the rate is to time how long it takes to produce a certain amount of sulphur. The exact amount of sulphur is not measured but it can be assumed that the same quantity of sulphur will be produced in order to obscure some writing on a piece of paper below the reaction vessel. You may be able to monitor the reaction using data logging equipment. Possible Investigations • Vary the concentrations of the reactants to investigate its effect on the rate of the reaction. You will be able to find the order of reaction for each reactant and hence the rate equation for the reaction. Investigate the reaction at different temperatures to determine the effect of temperature on the rate and hence determine the activation enthalpy for the reaction. Investigate the effect of iron (III) ions on the reaction -what is the catalytic effect? Vary the temperature and find the activation enthalpy for the catalysed reaction. Investigate a different technique for monitoring the rate of the reaction – possibilities are – light meter, pH or conductivity – you could link these instruments to a computer if it is available.
Sources of Information • • • • • • • • • • The Chemistry Video Consortium and The Royal Society of Chemistry (2000) Practical Chemistry for Schools and Colleges CD ROM Thorpe A, Making a standard solution, Chemistry Review, November 2002 Lindsey D, Measuring pH, Chemistry Review, September 1998 Ferguson M., Volumetric Analysis. Chemistry Review, September 1996 Farley R., (2001), School Chemistry Experiments, Association for...
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