Question 10
What is the formula mass of ammonium sulphate ((NH4)2SO4)? (Ar: H = 1, N = 14, O = 16, S = 32)
The right answer is the one marked above.
132. Inside the bracket NH4 = 14 + 4 = 18; the 2 outside acts on it, giving 18 × 2 = 36. So 36 + 32 + (4 × 16) = 36 + 32 + 64 = 132.
114 comes from ignoring the 2 outside the bracket and counting NH4 once. Where there is a bracket, the number outside it acts on everything inside.