CaCl₂. 3H₂O
We are given;
We are required to determine the formula of the hydrate;
First; we determine the mass of the anhydrous salt
Mass of anhydrous Calcium chloride = Mass of hydrate - mass of water
= 2.246 g - 0.728 g
= 1.518 g
Second; determine the moles of anhydrous salt and water
Moles = mass ÷ molar mass
Moles of anhydrous salt
Molar mass of CaCl₂ = 110.98 g/mol
Moles of CaCl₂ = 1.518 g ÷ 110.98 g/mol
= 0.0137 moles
Moles of water
Molar mass of water = 18.02 g/mol
Moles of water = 0.728 g ÷ 18.02 g/mol
= 0.0404 moles
Third; we determine the whole number mole ratio of anhydrous salt to water
CaCl₂ : H₂O
0.0137 moles : 0.0404 moles
0.0137/0.0137 : 0.0404/0.0137
1 : 2.95
1 : 3
Therefore, the formula of the hydrate is CaCl₂. 3H₂O
