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K_a1, K_a2 and K_a3 are the respective ionization constants for the following reactions (a), (b) and (c). (a) H2C2O4 ⇌ H+ + HC2O4− (b) HC2O4− ⇌ H+ + C2O4^2− (c) H2C2O4 ⇌ 2H+ + C2O4^2− The relationship between K_a1, K_a2 and K_a3 is given as
- (A) K_a3 = K_a1 + K_a2
- (B) K_a3 = K_a1 − K_a2
- (C) K_a3 = K_a1 / K_a2
- (D) K_a3 = K_a1 × K_a2
Correct answer: (B) K_a3 = K_a1 − K_a2
Solution
The correct option is based on the principle of combining equilibrium constants for sequential reactions. The third reaction (c) can be viewed as the sum of the first reaction (a) and the second reaction (b), leading to the relationship K_a3 = K_a1 - K_a2, as the second reaction effectively removes H+ from the equilibrium established by the first.
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