Question

a compound has oxygen equal to 61.32% sulphur equal to 11.15% hydrogen equal to 4.88% and zn equals to 22.65% the relative atomic mass of compound is 287 a.m.u. find the molecular mass of compound assuming that all the hydrogen is present as water of crystallization

Answer 1

The first step is to divide each elements percentage with it's atomic mass.
Zn will be 22.65/65.4 = 0.34
H will be 4.88/1 = 4.88
S will be 11.14/32.1 = 0.34
O will be 61.32/16 = 3.83

The second step is to divide the values by the smallest values you obtained.So,
Zn 0.34/0.34 = 1
H 4.88/0.34 = 14
S 0.34/0.34 = 1
O 61.32/0.34 = 11

So the molecular formula is ZnSO4 7H20. It is 7H20 as all hydrogen are in the form water of crystallization So it requires 7O and then O4 in the SO4. 

The molecular weight will be (16 X 11) + (32.1 X 1) + (1 X 14) + (65.4 X 1) which is equal to 287.

(P.S. don't worry I used full values to calculate this tho i simply wrote the working in 3 s.f.) 

Answer 2

This is the answer...i hope you got it