When equal volume of 1 M HCl and 1 M H₂ SO₄ are separately neutralised by excess volume of 1 M NaOH solution. x and y kJ of heat is liberated respectively. The value of y / x is __________.

Solution

Chemistry ma’am · 4 steps

Heat of neutralisation follows the moles of water formed, and the dibasic acid makes twice as much water.

1. What releases heat. For a strong acid and a strong base, the reaction that gives out heat is H⁺ + OH⁻ → H₂O, about 57.1 kJ per mole of water. So the heat liberated is proportional to the moles of H⁺ neutralised.
2. Count the H+. Take volume V litres of each acid. HCl is monobasic, so it gives 1 × V = V mol of H⁺. H₂SO₄ is dibasic, so it gives 2 × V = 2V mol of H⁺.
3. Excess NaOH. The base is in excess, so every H⁺ from each acid is neutralised and the acid alone decides how much water forms.

   y/x = (2V × 57.1)/(V × 57.1) = 2

4. So. H₂SO₄ releases twice the heat of HCl, and y/x = 2.

The common slip: 1. Treating both acids as giving the same moles of H⁺ because their molarity is equal gives 1, not 2. H₂SO₄ releases two H⁺ per molecule.

The idea to keep. Heat of neutralisation per mole of water is fixed for strong acid and strong base. Count the H⁺ that actually react, so basicity matters, not just molarity.

Answer from the NTA final answer key. Solution by PrepWiser.