Practical investigations

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How do you find the percentage of MgCO₃ in an indigestion tablet using
a) thermal decomposition
b) reaction with an acid
Plus could you include relative equations and safety precautions to help me with my question.

Igloo writes ...
In both cases you need to break down the tablet using heat or a dilute solution of, for example, hydrochloric acid. In both cases carbon dioxide is evolved:
 
MgCO₃(s) ----> MgO(s) + CO₂(g)
 
MgCO₃(s) + 2HCl(aq) ----> MgCl₂ (aq) + H₂O(l) + CO₂(g)
 
You can monitor these reactions by measuring either the volume of carbon dioxide evolved or the loss in mass of the chemicals. I suggest that you use one of these for the first of the reactions and the other procedure for the second. For example, you could measure the loss in mass occurring when a known mass of tablets is heated until there is no further change. In your second experiment you could add an excess of acid to a known mass of tablets and measure the volume of carbon dioxide evolved.
 
You will need to research suitable apparatus for yourself, and it will be necessary to carry out trial calculations and experiments to check that everything works before you start your actual experimental “runs”. The calculations I’ll leave to you!
 
We are not qualified to give safety advice on React. You must find other sources for this.
 
Always carry out a risk assesment 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 2007