Final answer:
To calculate the % mass of water in calcium chloride dihydrate, divide the mass of water in one mole of the compound by the molar mass of the compound and multiply by 100%. The % mass of water in calcium chloride dihydrate is 28.9%.
Step-by-step explanation:
To determine the % mass of water in calcium chloride dihydrate, we need to calculate the mass of water in one mole of calcium chloride dihydrate and express it as a percentage of the molar mass of the compound. Calcium chloride dihydrate (CaCl2 * 2H2O) consists of one mole of calcium chloride (CaCl2) and two moles of water (H2O).
The molar mass of calcium chloride dihydrate: 40.1 g/mol (Ca) + 2x 35.5 g/mol (Cl) + 2x 16.0 g/mol (H2O) = 110.6 g/mol
The mass of water in one mole of calcium chloride dihydrate: 2x 16.0 g/mol (H2O) = 32.0 g/mol
The % mass of water in calcium chloride dihydrate: (32.0 g/mol / 110.6 g/mol) x 100% = 28.9%