Practical investigations
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I have to react an acid with magnesium carbonate to find the % purity of magnesium carbonate in an indigestion tablet, using a gas syringe. I understand the method but I am unsure whether to use hydrochloric acid or sulphuric acid as obviously HCl is more relevant when talking about indigestion but at the same time I have been told that sulphuric acid is less likely to react with other compounds in the tablet so may be a better choice. I cannot find information on this property of sulphuric acid so I am unsure what to do - please help!
Your method only works if the only active ingredient in the tablet is magnesium carbonate. If you have a mixture of ingredients that react with acid you will not be able to interpret the results.
Some indigenstion tablets contain calcium carbonate. If so, the choice of acid matters. Calcium carbonate starts to react with sulphuric acid, but then the reaction slows down and stops as the particles of carbonate get coated with insoluble calcium sulphate. This is not a problem with calcium chloride because it is freely soluble in water.
Always carry out a risk assessment and check with your teacher before starting any practical work.
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: 28 January 2006
