Question

Use calculations to show what is the effect on the value of the water of hydration should you fail to completely dry your compound. Explain your answer.

Answer 1

Water of hydration is the number of water molecules that are chemically attached to a compond. For example, CuSO4.5H2O contains 5 molecules of water of crystallization.

Upon heating,

CuSO4.5H2O ---> CuSO4(s) + 5H2O

But upon incomplete heating,

CuSO4.5H2O ---> CuSO4.3H2O + 2H2O

This is called partial removal of water.

Due to this, there occurs an error in calculating the exact formula of the hydrate through the dehydration experiment, because the amount of water appers smaller than it actually is in the anhydrous compound.

In the second equation, due to experimental error we might consider CuSO4.3H2O to be the anhydrous compound, which it actually isn't.

As a result, in the formula :

%water in hydrate = (mass of water driven off / mass of hydrated compound)

mass of water driven off is less because of the error.

If you assume the formula as CuSO4.'x'H2o and your task is to find out 'x' through the experiment, the formula we use is :

x = Moles of water/moles of anhydrous CuSO4

Since moles of anhydrous CuSO4 from the experiment is larger than it should actually be , so the vale of 'x' we obtain is smaller, hence the wrong result.

Hope this helps !