On heating, the hydrated salt CaSO4, xH2O loses its water of crystallization. In anexperiment it was found that when 0.2 mol of the hydrated salt was heated 0.10mol of water was lost. What is the molecular formula of the hydrated compound?
Correct answer: B. CaSO3. 1⁄2 H2O
- A. CaSO4
- B. CaSO3. 1⁄2 H2O
- C. CaSO4.H2O
- D. CaSO4.2H2O
Explanation
The number of water molecules associated with the hydrated salt can be determined by the ratio of moles of water lost to moles of the hydrated salt.Given:Moles of hydrated salt (CaSO4 ⋅xH2 O) = 0.2 molMoles of water lost (H2 O) = 0.10 molFind the ratio of moles of water to moles of the hydrated salt: Ratio=Moles of water/Moles of hydrated saltRatio=0.10 mol0.2 mol=0.5The ratio represents the number of water molecules per formula unit of the hydrated salt. Therefore, x inCaSO4 ⋅xH2 O is 0.5.The molecular formula of the hydrated compound is CaSO4 ⋅0.5H2 O, which can be simplified to 2CaSO4 ⋅1⁄2H2 O.Therefore, the correct answer is:b. 2CaSO4 ⋅1⁄2H2 O
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