Question

A sample of hydrated cobalt (II) chloride has a mass of 5.22 g. After heating, it has a mass of 2.85 g. What is the percent by mass of water in the hydrate?

Answer 1

Answer: The percent by mass of water in the hydrate is 45.4 %

Explanation:

The chemical equation for the heating of hydrated cobalt (II) chloride follows:

$CoCl_2.xH_2O\rightarrow CaCl_2+xH_2O$

We are given:

Mass of hydrated cobalt (II) chloride = 5.22 g

Mass of anhydrous cobalt (II) chloride = 2.85 g

Mass of water released = (5.22 - 2.85)g = 2.37 g

To calculate the mass percentage of water in the hydrate, we use the equation:

$\text{Mass percent of water}=\frac{\text{Mass of water}}{\text{Mass of hydrated cobalt (II) chloride}}\times 100$

Mass of hydrated cobalt (II) chloride = 5.22 g

Mass of water = 2.37 g

Putting values in above equation, we get:

$\text{Mass percent of water}=\frac{2.37g}{5.22g}\times 100=45.4\%$

Hence, the percent by mass of water in the hydrate is 45.4 %

Answer 2

Answer:
mass of water in hydrate = 2.37 grams

Explanation:
The mass of the hydrated cobalt (III) chloride is the summation of the salt and the water it contains.
This means that:
Total mass of sample = mass of salt + mass of water

Now, we are given that:
total mass of sample = 5.22 grams
mass of salt = mass of sample after heating = 2.85 grams

Substitute to get the mass of water as follows:
5.22 = mass of water in hydrate + 2.85
mass of water in hydrate = 5.22 - 2.85
mass of water in hydrate = 2.37 grams

Hope this helps :)