What is the % ionisation of hypochlorous acid in a 0.015M solution at 25°C?

[NOP90]

Homework Statement

The Ka of hypochlorous acid (HClO) is 3.0*10^-8 at 25 degrees C. What is the % ionisation of hypochlorous acid in a 0.015M aqueous solution of HClO at 25 degrees Celcius

The answer is 0.14

Homework Equations

-log[H+], n = cV, pH = pKa + log (base/acid), x/y*100=%

The Attempt at a Solution

I tried -log3*10^-8 and got 7.5. Not to sure what to do with that.

 

[symbolipoint]

Was the "0.015" actually the FORMAL concentration of the acid? If we assume that the concentration really was meant as 0.015M of the weak acid, then

\[<br /> \frac{{\left[ x \right]\left[ x \right]}}{{0.015 - x}} = Ka = 3 \times 10^{ - 8} <br /> \]<br />, where x represents approximately the amount of moles per liter of HClO which actually ionizes.

 

[Borek]

NOP90, have you heard about ICE tables?