Practical investigations
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If magnesium carbonate in an indigestion tablet is diluted to a 250 cm3 solution will it act as an alkali and can I then titrate it against sulphuric acid to find the percentage purity of the magnesium carbonate?
Igloo writes
Unlike sodium and potassium carbonates which dissolve in water, magnesium carbonate is highly insoluble, so it is not possible to make it up into a solution and titrate with sulphuric acid as you suggest.
There are several ways in which you can determine the quantity of magnesium carbonate present in an indigestion tablet, and if you wish to use a titration technique proceed as follows:
[1] Weigh out your tablet(s) accurately.
[2] Transfer the crushed tablet(s) to a conical flask and add a measured volume of dilute sulphuric acid of known concentration, perhaps 0.50 mol dm-3. It is vital that the volume used is an excess, so that all the magnesium carbonate is destroyed. I’ll leave you to design a procedure which ensures that an excess of acid has been used.
[3] After the reaction has subsided, titrate the mixture with a solution of sodium hydroxide of known concentration, e.g. 0.50 mol dm-3, using a suitable indicator.
[4] The titration reading will enable you to calculate the quantity of sulphuric acid remaining after its earlier reaction with the indigestion tablet(s). Hence you can deduce the quantity of sulphuric acid used to destroy the magnesium carbonate and finally it will be possible to calculate the percentage of this material in the tablet(s).
In this method it has to be assumed that magnesium carbonate is the only carbonate present in indigestion tablets.
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Risk assessment
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updated: 19 January 2006
