Question

A sample of hydrated calcium sulfate has a mass of 20.88 g. After it is heated, it has a mass of 16.51 g. What is the percentage by mass of water in the hydrate? Use the formula mc010-1.jpg 4.37% 20.9% 26.5% 43.7%

Answer 1

We know that when you heat up calcium sulfate all the water has evaporated from it. That means that the mass of water that was initially in the sulfate is the difference in mass of the sulfate before and after the heating.
$m{_H__20}=20.88-16.51=4.37g$
In order to get a percentage by mass we simply divide this number by the initial amount of sulfate:
$\%_{H__2}O=\frac{4.37}{20.88}=20.93\%$

Answer 2

The answer is B) 20.9%