Why is Ka2 << Ka1 for H2SO4 in water?

H₂SO₄ ionises in two stages and hence has two dissociation constants. K_a2 << K_a1.

This is because the negatively charged HSO₄^- ion has much less tendency to donate a proton to H₂O as compared to neutral H₂SO_4.

(i) (a) NH₄Cl (aq.)+ NaNO₂ (aq. ) →N₂(g) +2H₂O(l) +NaCl(aq.) 

(b) P₄ + 3NaOH + 3H₂O→ 3NaH₂PO₂ + PH₃

(iii) H₂SO₄ is a very strong acid in water because of its first ionisation to H₃O⁺ and HSO₄^-. The ionization of HSO₄^- to H₃O⁺ and SO₄^2- is very small (it is difficult to remove a proton from a negatively charged ion).

H₂SO₄ is dibasic acid. It ionises in two stages and hence has two dissociation constants as given below:
(i) H₂SO_4(aq) + H₂O_(l) → H₃O⁺_(aq) + HSO^–_4(aq) ; Ka₁ > 10
(ii) HSO^–_4(aq) + H₂O_(l) → H₃O⁺_(aq) + SO^2-_4(aq) ; Ka₂ = 1.2 x 10^-2
Ka₁ is greater than Kay, i.e., tendancy to move towards the products is greater in (i) than in (ii). This is because the negatively charged HSO^–₄ ion has much less tendancy to donate a proton to H₂O as compared to neutral H₂SO₄.