Question

A 7.028 gram sample of a sodium sulfate hydrate is heated. After driving off all the water, 3.100 grams of the anhydrous salt is left. What is the name of the hydrate?

Answer 1

`NaSO_4.10H_2O`

Step-by-step explanation:

Given that:-

Mass of the hydrated salt = 7.028 g

Mass of the anhydrous salt = 3.100 g

Mass of water eliminated = Mass of the hydrated salt - Mass of the anhydrous salt = 7.028 - 3.100 g = 3.928 g

Moles of water:

Mass of water = 3.928 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= (3.928\ g)/(18\ g/mol)`

`moles_(water)= 0.2212\ mol`

Moles of anhydrous salt:

Amount = 3.100 g

Molar mass of
`NaSO_4` = 142.04 g/mol

Thus, moles are:

`moles= (3.100\ g)/(142.04\ g/mol)`

`moles_(CaSO_4)= 0.02182\ mol`

The simplest ratio of the two are:

`NaSO_4:H_2O` =0.02182 : 0.2212 = 1 : 10

Hence, the formula for hydrate is:-
`NaSO_4.10H_2O`