20 cm3 of an aq 1.0 mol/dm3 solution of the hydroxide of metal X requires 40 cm3 of aq 0.25 mol/dm3 of sulfuric acid for complete neutralisation.
What is the formula for the sulfate of X?
A) X2SO4
B) XSO4
C) X2(SO4)3
D) X(SO4)2
Answer: A
Approach: calculate the no. of moles of X hydroxide and sulfuric acid and then compare the mole ratio.
By comparing mole ratio: 2 mol of X hydroxide reacted with 1 mol of sulfuric acid → X hydroxide must be XOH (monobasic).
2XOH + H2SO4 → X2SO4 + 2H2O
Essentially, neutralisation is represented by H+ + OH– → H2O i.e. 1 mol H+ reacts with 1 mol OH–, hence:
one mol of monobasic acid (one H+) will react with one mol monobasic base (one OH–)
one mol of dibasic acid (two H+)will react with two mol monobasic base (two OH–)
two mol of monobasic acid (two H+) will react with one mol dibasic base (two OH–)
...
