20 mL of 0.244 M hypochlorous acid (HClO) has been titrated with 0.150 M of sodium hydroxide. How can I find pH?

The Ka of the solution is 3.0 * 10^-8.
How do I calculate the pH of the solution once 10mL of the 0.150 M has been added? Which equation should I use in order to find the correct answer? Thanks!

1 Answer
May 5, 2018

Given,

Consider the equilibrium,

#HClO + HO^(-) rightleftharpoons H_2O + ClO^(-)#

Where #K_"a" = 3*10^-8#, only regarding hypochlorous acid. (If that didn't make sense, comment and I can explain more)

Let's assume that the hydroxide ions will consume one equivalent of hypochlorous acid protons.

puu.sh

Now, recall,

#"p"H = "p"K_"a" + log(([A^-])/([HA]))#

where,

#[A^-] = [ClO^-]_"eq" = 1.5*10^-3"M"#,

#[HA] = [HClO]_"eq" = 3.4*10^-3"M"#, and

#"p"K_"a" = 7.52#

Hence,

#"p"H = "p"K_"a" + log(([ClO^-])/([HClO])) approx 7.17#

at this point in the titration curve.