Question

What is the ratio of acetate ion to acetic acid (Ka = 1.76×10–5) in a solution containing these compounds at pH 4.38 ? Write your answer as a decimal and not as a fraction.

Answer 1

Answer:

0.43.

Explanation:

In order to solve this question we will need the an equation called Henderson-Hasselbalch Equation. The Henderson-Hasselbalch Equation can be represented by the reaction below;

pH= pKa + log ( [ A^- ] / [ HA] ).

Where HA is the acetic acid and A^- is the Acetate ion

We are given the pH value to be = 4.38 and the ka to be = 1.76×10^–5. So, we will use the value for the ka to find the pKa through the formula below.

pKa = - log ka.

Therefore, pKa = - log( 1.76×10^–5).

pKa= 4.75 + log

So,

4.38 = 4.75 + log ([ A^-] / [HA]).

4.38 - 4.75 = log ( [ A^- ] / [ HA] ).

( [ A^- ] / [ HA] ) = 10^- 0.37.

( [ A^- ] / [ HA] ) = 0.42657951880159265.

( [ A^- ] / [ HA] )= 0.43.