Question

Given information:

MgSO4: mass of crucible (26.41g) mass of crucible and hydrate (36.37 g) mass of crucible and anhydrate after heating (31.45 g)

CuSO4: mass of crucible (18.21g) mass of crucible and hydrate (30.16 g) mass of crucible and anhydrate after heating (27.89 g)

Show the calculations:

(1) Mass of hydrate used (2) Mass of anhydrate after heating (3) Mass of water driven off from hydrate (4) Percent water in the hydrate

(5) Number of moles of water driven off from the hydrate (6) Number of moles of adhydrate in the product (7) Mole ration of anhydrate to water

(8) Empirical formula of the hydrate

Answer 1

In MgSO4

Mass of hydrate used = mass of crucible and hydrate - mass of crucible

= 36.37 - 26.41

= 9.96 g

Mass of anhydrate after heating = mass of crucible and anhydrate after heating - mass of crucible

= 31.45 - 26.41

= 5.04 g

Mass of water driven off from hydrate = Mass of hydrate - Mass of anhydrate after heating

= 9.96 - 5.04

= 4.92 g

Percent water in the hydrate = Mass of water lost x 100 / mass of hydrate

= 4.92*100/9.96

= 49.4%

Number of moles of water driven off from the hydrate

= mass of water lost / molecular weight

= 4.92/18 = 0.273 mol

Number of moles of adhydrate in the product

= 5.04/120.366

= 0.04187 mol

Mole ratio of anhydrate to water = 1 : 6.53

Multiply by 2

Mole ratio of anhydrate to water = 2 : 13

Empirical formula of the hydrate = 2MgSO4·13H2O

In CuSO4

Mass of hydrate used = mass of crucible and hydrate - mass of crucible

= 30.16 - 18.21

= 11.95 g

Mass of anhydrate after heating = mass of crucible and anhydrate after heating - mass of crucible

= 27.89 - 18.21

= 9.68 g

Mass of water driven off from hydrate = Mass of hydrate - Mass of anhydrate after heating

= 11.95 - 9.68

= 2.27 g

Percent water in the hydrate = Mass of water lost x 100 / mass of hydrate

= 2.27*100/11.95

= 19%

Number of moles of water driven off from the hydrate

= mass of water lost / molecular weight

= 2.27/18 = 0.126 mol

Number of moles of adhydrate in the product

= 9.68/159.609

= 0.06065 mol

Mole ratio of anhydrate to water = 1 : 2.07

Empirical formula of the hydrate = CuSO4·2H2O