Inorganic reactions
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I am given a salt of magnesium sulphate with an impurity of potassium nitrate. How can I calculate the percentage by mass of the impurity via experiment?
Corrie writes .....
Both the salts are soluble in water. Adding an excess of a soluble barium salt (e.g. nitrate or chloride - CARE: soluble barium salts are TOXIC), to a solution of the mixture will produce a white precipitate of very insoluble barium sulphate.
Separating out the barium sulphate and finding its dry mass will enable you to calculate the number of moles of it formed. This will be equal to the number of moles of of magnesium sulphate, and hence the mass of magnesium sulphate, present in the mixture. From this you can calculate the mass of the impurity and its percentage.
I'll leave you to deal with the relevant equations and how to separate the barium sulphate and purify and dry it.
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updated: 20 August 2007
