Question

Suppose you have a mixture of solid potassium chloride and magnesium carbonate. The physical and chemical properties of potassium chloride are similar to those of sodium chloride, and the properties of magnesium carbonate are similar to those of calcium carbonate.

a.draw a flowchart that shows how you would separate and recover the two components of this mixture.

Answer 1

The major difference between these two salts that can be exploited for their separation is their solubility in water. Potassium chloride is freely and highly soluble in water while magnesium carbonate has a very low solubility of 0.0139g/100mL of water at STP, which can be taken for practical purposes as insoluble when we consider KCl with a solubility of 35.5g/100mL of water again at STP.

Therefore, the given mixture of salts can be dissolved a bare minimum quantity of water to give a pure precipitate of magnesium carbonate, which will remain insoluble in water after KCl has saturated the aqueous phase. This precipitate can be filtered out and dried to obtain magnesium carbonate. The water soluble potassium chloride can now be got by simple evaporation of water from the KCl solution which results in crystals of the pure salt as water starts boiling off. Since the salt is highly stable, boiling the salt solution will not result in any decomposition.

If this method is carried out deionized water, pure and precise quantities of each salt can be obtained and from the weight of the mixture and the weight of individual salts, their mass percentage can also be calculated.