Chapter 10.5, Problem 78SSC

Interpretation Introduction

Interpretation:

The experimental procedure for determining formula of a hydrate needs to be explained.

Concept introduction:

The relation between number of moles, mass and molar mass of a substance is represented as follows:

$n=\frac{m}{M}$

Here, m is mass and M is molar mass.

Explanation of Solution

In the first step, the mass of hydrated salt needs to be determined using the measuring cylinder. A crucible is prepared by heating to remove water molecules present in it. The mass of empty crucible should be noted.

Now, the calculated mass of hydrated salt is put into the crucible. The mass of crucible and hydrated salt is taken.

The hydrate is heated strongly to remove the water molecules present in it. The mass of the crucible is measured again. The obtained mass will be sum of the mass of crucible and anhydrous salt. Thus, the mass of anhydrous salt can be determined by subtracting the mass of crucible recorded at the starting of the experiment.

Now, by subtracting the mass of anhydrous salt from the hydrated salt, the mass of water can be obtained. Using the molar mass of water, number of moles of water molecules can be determined.

Thus, the formula of hydrate can be obtained.