Question

A hydrate is determined to be 45.43% water and 54.57% CoCl. Find the chemical formula and name for this hydrate. (*Hint - assume that there is 100 g total of hydrate compound.) TUCK

Answer 1

Answer : The chemical formula for the given compound is
`COCl_2.6H_2O`

Explanation : Given,

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of
`H_2O` = 45.43 g

Mass of
`COCl_2` = 54.57 g

Molar mass of
`H_2O` = 18 g/mole

Molar mass of
`COCl_2` = 129.9 g/mole

To formulate the chemical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of water =
`\frac{\text{Given mass of water}}{\text{Molar mass of water}}=(45.43g)/(18g/mole)=2.524moles`

Moles of
`COCl_2` =
`\frac{\text{Given mass of }COCl_2}{\text{Molar mass of }COCl_2}=(54.57g)/(129.9g/mole)=0.4201moles`

Step 2: Calculating the mole ratio of the given molecule.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.4201 moles.

For
`H_2O` =
`(2.524)/(0.4201)=6.00\approx 6`

For Carbon =
`(0.4201)/(0.4201)=1`

Step 3: Taking the mole ratio as their subscripts.

The ratio of
`COCl_2:H_2O` = 1 : 6

The chemical formula for the given compound is
`(COCl_2)_1(H_2O)_6=COCl_2.6H_2O`

Hence, the chemical formula for the given compound is
`COCl_2.6H_2O`