Question

A $250$ g sample of a hydrated salt was heated at ${110}^{o}C$ until all water was driven off. The remaining solid weighed $160$ g. From these data, the percent of water by weight in the original sample can be correctly calculated as :

• A. $\frac{160}{340}\times 100$ %
• B. $\frac{90}{340}\times 100$ %
• C. $\frac{160}{250}\times 100$ %
• D. $\frac{90}{250}\times 100$ %
• E. $\frac{90}{160}\times 100$ %

Answer 1

Answer: (D)

$\frac{90}{250}\times 100$ %

The percent of water by weight in the original sample can be correctly calculated as :
$=\frac{\text{mass of water}}{\text{mass of hydrated sample}}\times 100$
$=\frac{\text{mass of hydrated sample}-\text{mass of anhydrous sample}}{\text{mass of hydrated sample}}\times 100$
$=\frac{250-160}{250}\times 100$
$=\frac{90}{250}\times 100$