Question

A sample of hydrated salt is heated at ${110}^o$C for $30$ minutes until all the water is driven off. The recorded data is as follows:
Mass of the hydrate before heating$=250$ grams
Mass of the hydrate after heating$=160$ grams
From the above data, what is the percentage of water by mass in the original sample?

• A. $26.5$%
• B. $36$%
• C. $47$%
• D. $56$%
• E. $90$%

Answer 1

Answer: (B)

$36$%

From the mass of the hydrate before heating, the mass of the hydrate after heating is subtracted to get the mass of water.
The mass of water $250-160=90$ g
The percent of water by mass in the original sample is $\frac{90}{250}\times 100=36$ %.