[xangelofxdeathx]

HOCl_(aq)  <-----> H_+(aq) + OCl^-_(aq)

The ionization of hypochlorous acid represented above has K = 3.0 * 10^-8 at 25 degrees Celsius. What is K for this reaction?

OCl^-_(aq) + H₂O_(l)  <-----> HOCl_(aq) + OH^-_(aq)

A) 3.3 * 10^-7
B) 3.0 * 10^-8
C) 3.0 * 10^-6
D) 3.3 * 10⁷



How do I do this problem? (The answer is A by the way)

[Yggdrasil]

In terms of [HOCl], [H⁺] and [OCl^-], what is K for the first reaction?

In terms of concentration variables, what is K for the second reaction?

What would you manipulate the first K by in order to get the second K?

Alternatively, you can think of how you would manipulate the first chemical equation in order to get the second.

[xangelofxdeathx]

Hmm, well at first I said that the 2nd reaction is simply adding an OH^- to both sides of the 1st equation, which doesn't change the K value, and then reversing the reaction, which would make the K value 1/K.

So 1/(3.0 * 10^-8) = 3.3 * 10⁷.

However, that isn't the answer according to the answer manual, so where am I going wrong?

[xangelofxdeathx]

Ohhhh, I see what you mean now.

K of 1st reaction = [OCl^-][H⁺]/[HOCl]

K of 2nd reaction = [OH^-][HOCl^-] / [OCl^-]

and then manipulating the 1st reaction ---> [HOCl^-] / [OCl^-] = [H⁺] (1 / 3.0 * 10^-8)

and then plugging it into 2nd reaction ---> K of 2nd reaction = [OH^-][H⁺] (1 / 3.0 * 10^-8)

and using the fact that [OH^-][H⁺] = 10^-14

the answer comes out 3.3 * 10^-7

Thank you   

[Yggdrasil]

Exactly.  This is the equivalent to reversing the original equation, then adding the autoionization of water:

H⁺ + OCl^- --> HOCl             1/K₁
H₂O --> H⁺ + OH^-               K_w
----------------------------------------------------------------------
OCl^- + H₂O --> HOCl + OH^-   K₂ = K_w/K₁

[AWK]

HOCl_(aq)  <-----> H_+(aq) + OCl^-_(aq)

The ionization of hypochlorous acid represented above has K = 3.0 * 10^-8 at 25 degrees Celsius. What is K for this reaction?

OCl^-_(aq) + H₂O_(l)  <-----> HOCl_(aq) + OH^-_(aq)

A) 3.3 * 10^-7
B) 3.0 * 10^-8
C) 3.0 * 10^-6
D) 3.3 * 10⁷



How do I do this problem? (The answer is A by the way)

K_w/K_a