Question

1.6 M H2SO4 is carelessly substituted for 6 M HCl. Will more or fewer drops of 6 M H2SO4 be required for the litmus to change color?

Answer 1

Answer is: fewer drops of 6 M sulfuric acid, because concentration of H⁺ is greater than in hydrochloric acid with same concentration.

Chemical dissociation of hydrochloric acid in water: 
HCl(aq) → H⁺(aq) + Cl⁻(aq).
Chemical dissociation of sulfuric acid in water: 
H₂SO₄(aq) → 2H⁺(aq) + SO₄²⁻(aq).
From chemical reaction: c(HCl) = c(H⁺) = 6 M.
c(H⁺) = 2c(H₂SO₄) = 2 · 6 M = 12 M; concentration of hydrogen cations.