What is the percent by mass of Water in CaSO4•2H20?

20.93%

Explanation:

The percent by mass (%mass) of water in the following compound can be calculated thus:

%mass of H2O = mass of 2H2O/mass of compound × 100

Where;

Ca = 40

S = 32

O = 16

H = 1

Hence, the molar mass of CaSO4•2H20 = 40 + 32 + 16(4) + 2{ 1(2) + 16}

= 40 + 32 + 64+ 2{18}

= 172g/mol

Molar mass of 2H2O = 2{2 + 16}

2(18)

= 36g/lol

Therefore, the percent by mass of 2H2O in CaSO4•2H20 is as follows:

36/172 × 100

= 0.2093 × 100

= 20.93%

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