Practical investigations
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I'm doing an investigation into the techniques for monitoring the rate of reaction of thiosulphate and various acids, such as pH and conductivity. However, no-one else seems to be doing this. Has it been done in the past? It's very difficult for me to find any pointers on how to go about this investigation!
Jenkin replies
When a solution of sodium thiosulphate (which is what I imagine you will use as your source of thiosulphate ions) reacts with an acid, one of the products is sulphur which you will see as a precipitate. This appears quite suddenly, so you can use the time taken from mixing the solutions until the appearance of the precipitate as a method of monitoring rate.
pH, conductivity, etc are not easily applied to this reaction.
You can find some practical details in the Nuffield Chemistry Students’ Book, pages 256-257 (Experiment 11.4). This particular experiment investigates the effect of temperature on the reaction, but it could easily be adapted to look at other things, such as using different acids.
Remember that you must vary only one factor at a time, so keep the temperature constant, perhaps by using a water bath. Think carefully about what acids you will use and notice that in the equation for the reaction it is hydrogen ions, H+ which is the reacting species from the acid.
Preliminary work could be to establish suitable concentrations of solutions to give sensible reaction times.
Read safety warnings in the book, or another reliable source. Carry out a Risk Assessment before you do any laboratory work and check with your teacher.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 11 November 2004
