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(A) The chemical formula for gypsum is $CaSO_4 \cdot 2H_2O$ and for plaster of Paris is $CaSO_4 \cdot \frac{1}{2}H_2O$. To calculate the percentage of

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The percentage of calcium in gypsum is lower than in plaster of Paris.

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(A) The chemical formula for gypsum is $CaSO_4 \cdot 2H_2O$ and for plaster of Paris is $CaSO_4 \cdot \frac{1}{2}H_2O$. To calculate the percentage of calcium: Molar mass of $CaSO_4 \cdot 2H_2O = 40 + 32 + (4 	imes 16) + 2 	imes (2 + 16) = 172 \ g/mol$. Percentage of $Ca = (40 / 172) 	imes 100 \approx 23.26\%$. Molar mass of $CaSO_4 \cdot \frac{1}{2}H_2O = 40 + 32 + (4 	imes 16) + 0.5 	imes 18 = 145 \ g/mol$. Percentage of $Ca = (40 / 145) 	imes 100 \approx 27.59\%$. Since $23.26\% Thus,option $A$ is correct.

Select the correct statement from the following.

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