Question

Epsom salts is a hydrated ionic compound with the following formula: MgSO4⋅x H2O. A 4.93-g sample of Epsom salts is heated to drive off the water of hydration. The mass of the sample after complete dehydration is 2.41 g. Find the number of waters of hydration (x) in Epsom salts.

Answer 1

number of water molecules are 7

Step-by-step explanation:

Mass of the hydrated salt = 4.93 g

Mass of the dehydrated salt = 2.41 g

Mass of water lost = 4.93 - 2.41 g = 2.52 g

The moles of the dehydrated salt is :

Amount = 2.41 g

Molar mass of
`MgSO_4` = 120 g/mol

The formula for the calculation of moles is shown below:

`moles = (Mass\ taken)/(Molar\ mass)`

Thus, moles are:

`moles= (2.41\ g)/(120\ g/mol)`

`moles= 0.02\ mol`

The moles of water is :

Amount = 2.52 g

Molar mass of
`H_2O` = 18 g/mol

The formula for the calculation of moles is shown below:

`moles = (Mass\ taken)/(Molar\ mass)`

Thus, moles are:

`moles= (2.52\ g)/(18\ g/mol)`

`moles= 0.14\ mol`

The simplest ration of the two are:

`MgSO_4:H_2O` = 0.02 : 0.14 = 1 : 7

The formula is
`MgSO_4.7H_2O`

So, number of water molecules are 7