4. A hydrate of zinc sulfate, ZnSo4 XH2O, decomposes to produce 43.9% water. Cal

Question

4. A hydrate of zinc sulfate, ZnSo4 XH2O, decomposes to produce 43.9% water. Calculate the water of crystallization (X) and write the formula for the hydrate.
5. A hydrate of calicum sulfate, CaSO4 XH2O, comtains 20.9% water, Calculate the water of crystallization (X) and write the formula for the hydrate.
6. Plaster of Paris, CaSO4 XH2O, is a fractional hydrate, that is, one water molecule attaches to more than one formula unit. If a 2.002g sample has a mass of 1.878g after heating, find the water of crystallization (X) and write the formula forPlaster of Paris.

Explanation / Answer

start with the assumptioon that you have 100g hydrated compound Then you will have 43.9g H2O 56.1 g ZnSO2 Molar mass ZnSO4 = 161.4726 g/mol 56.1g = 56.1/161.4726 = 0.347mol Molar mass H2O = 18.0153 43.9g H2O = 43.9/18.0153 = 2.4368 Divide by smaller value: ZnSO4 = 1 H2O = 7 Formula = ZnSO4.7H2O The second is done in exactly the same way: Mass CaSO4 = 79.1g Mass H2O = 20.9g Moalr mass CaSO4 = 136.1416 g/mol 79.1g CaSO4 = 79.1/136.1416 = 0.581 Molar mass H2O = 18.0153g/mol 20.9g H2O = 20.9/18.0153 = 1.160 Divide by smaller: CaSO4 = 1 H2O = 2 Formula = CaSO4.2H2O

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