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(A) The chemical formula of Gypsum is $CaSO_4 \cdot 2H_2O$ and Plaster of Paris $(POP)$ is $CaSO_4 \cdot \frac{1}{2}H_2O$. $POP$ is prepared by heatin

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Gypsum contains a lower percentage of calcium than in Plaster of Paris

Vedclass · Answer

(A) The chemical formula of Gypsum is $CaSO_4 \cdot 2H_2O$ and Plaster of Paris $(POP)$ is $CaSO_4 \cdot \frac{1}{2}H_2O$. $POP$ is prepared by heating gypsum at $393 \ K$: $CaSO_4 \cdot 2H_2O(s) \xrightarrow{393 \ K} CaSO_4 \cdot \frac{1}{2}H_2O(s) + \frac{3}{2}H_2O(g)$. Option $A$ is correct because the molar mass of $CaSO_4 \cdot 2H_2O$ is $172 \ g/mol$ and $CaSO_4 \cdot \frac{1}{2}H_2O$ is $145 \ g/mol$. The percentage of calcium in gypsum is $(40/172) 	imes 100 \approx 23.25\%$,while in $POP$ it is $(40/145) 	imes 100 \approx 27.58\%$. Thus,gypsum has a lower percentage of calcium.

Identify the correct statement from the following.

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