Question

It is often possible to change a hydrate into an anhydrous compound by heating it to drive off the water (dehydration). A 45.91 gram sample of a hydrate of MnSO4 was heated thoroughly in a porcelain crucible, until its weight remained constant. After heating, 37.07 grams of the anhydrous compound remained. What is the formula of the hydrate

Answer 1

Answer: The formula of the hydrate is
`MnSO_4.2H_2O`

Step-by-step explanation:

Decomposition of hydrated manganese sulphate is given by:

`MnSO_4.xH_2O\rightarrow MnSO_4+xH_2O`

Molar mass of
`MnSO_4` = 151.0 g/mol

According to stoichiometry:

(151.0+18x) g of
`MnSO_4.xH_2O` decomposes to give 151.0 g of
`MnSO_4`

Thus 45.91 g of
`MnSO_4.xH_2O` decomposes to give=
`( 151.0)/(151.0+18x)* 45.91g` of
`MnSO_4`

Also we are given : 37.07 g of
`MnSO_4` is produced

Thus we can equate the two equations:

`( 151.0)/(151.0+18x)* 45.91=37.07`

`x=2`

Thus the formula of the hydrate is
`MnSO_4.2H_2O`