Answer to Question #32915 in Inorganic Chemistry for Joy

Question

1.61 grams of an hydrated salt BxH2O gave 0.714 grams of the an hydrous salt when heated. What will be the value of x if the relative molecular mass of B is 142?

Answer 1

An hydrous salt is B.
If m(B) = 0.714 grams
M(B) = 142 g/mol
So, n(B) = m/M
n(B) = 0.714 g / 142g/mol = 0.005 mol;
We see, that
n(B) : n(BxH₂O) = 1 : 1;
So, n(BxH₂O) = 0.005 mol;
m(BxH₂O) = 1.61 grams
By the formula
M = m/n
we can find the molecular mass of an hydrated salt
M(BxH₂O) = 1.61 g / 0.005 mol = 322 g/mol
M(xH₂O) = M(BxH₂O) - M(B);
M(xH₂O) = 322 g/mol - 142 g/mol = 180 g/mol
if M(H₂O) = 18 g/mol
x = M(xH₂O) / M(H₂O)
x = 180 / 18 = 10
Answer: x = 10