Question

Calculate the percentage of water in each of the following hydrates:
a) NaNbO3 ⋅ 7H2O
b) Co(CN)3 ⋅ 3H2O
c) Na2CrO4 ⋅ 4H2O

Answer 1

First you need to calculate the molecular weight of each compound then you can compute the percentage composition of water in each case.

NaNbO3 . 7H2O  = 290

Co(CN)3 . 3H2O  = 191

Na2CrO4 . 4H2O  = 234

percentage of water in each of the following hydrates:  

a) NaNbO3 ⋅ 7H2O  = 126/290 x 100 = 43.4%

b) Co(CN)3 ⋅ 3H2O  = 54/191 x 100    = 28.3%

c) Na2CrO4 ⋅ 4H2O = 72/234 x 100  = 30.8%