Question

Find % composition of (NH4)2 SO4

Answer 1

You calculate the mass of each atom in a formula unit, divide by the formula mass, and multiply by 100 %.

See What does percent composition mean?

For calculation purposes, we can write the formula of (NH₄)₂S as N₂H₈S.

Mass of N = 2 atoms N × 14.01u1atom N = 28.02 u

Mass of H = 8 atoms H × 1.008u1atom H = 8.064 u

Mass of S = 1 atom S × 32.06u1atom S = 32.06 u

Mass of (NH₄)₂S = (28.01 + 8.064 + 32.06) u = 68.144 u

% S =28.02u68.144u × 100 % = 41.12 %

% H =8.064u68.144u × 100 % = 11.83 %

% N =32.06u68.144u × 100 % = 47.05 %