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JEE MainChemistryIonic Equilibrium

An aqueous solution contains a mixture of two weak monoprotic acids, HA and HB . The concentration of HA is 0.2 M with an acid dissociation constant K_ a1 = 2 10⁻⁵ . The concentration of HB is 0.1 M with K_ a2 = 5 10⁻⁵ . The pH of the solution is x 10⁻² . The value of x is ____. (Nearest integer) [Given: 3 = 0.48 ]

Correct answer

252

Step-by-step solution

For a mixture of two weak acids, the hydrogen ion concentration is given by: [ H ^+] = K_ a1 C₁ + K_ a2 C₂ [ H ^+] = (2 10⁻⁵)(0.2) + (5 10⁻⁵)(0.1) [ H ^+] = 4 10⁻⁶ + 5 10⁻⁶ = 9 10⁻⁶ = 3 10⁻³ M pH = - [ H ^+] = - (3 10⁻³) pH = 3 - 3 = 3 - 0.48 = 2.52 pH = 252 10⁻² Thus, x = 252 . Answer: 252

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