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Question

A mixture of potassium chlorate and sodium chlorate has a mass of 7.5000 grams. When this mixture is heated to decompose it, the mass of the residue that remains after heating is 4.3091 grams. Determine the percentage of potassium chlorate in the original mixture. The balanced chemical equations for the reactions that occur during the heating are:



2 KClO3(s)→ KCl(s) + 3 O2(g)

2 NaClO3(s)→ 2 NaCl(s) + 3 O2(g)

Answer 1

This is a book keeping problem. Think of it as a problem in algebra, rather than in chemistry.

You have y g KClO3 and 7.5000 - y g NaClO3.

Divide by formula weights to give you moles of each (in terms of y)

Each chlorate gives rise to one chloride, so multiply your number of moles of KClO3 by 1 to get moles of KCl and then by the formula weight of KCl to get g KCl in terms of y. do the same for NaCl.

g KCl + g NaCl = mass of residue

The arithmetic is messy, but this is just a linear equation in y. Your answer is y/7.5000 x 100%

Principle: when comparing amounts of one substance with another (in this case amounts of the chlorates and chlorides), balance number of moles according to the reaction equation.

Good luck!