Chapter 16.9, Problem 2RC

Interpretation Introduction

Interpretation:

The strongest acid should be identified given the two different of iron (Fe) coordination complex molecules.

Concept introduction:

Strong acid: Acid solutions contains hydrigen ions, the higher concentration of hydrogen ions, the lower $pH$ for example hydrochloric acid is strong acid when comapre to acetic acid it is a weakr acid. Hence srong acids are completely ionizaes but weak acids are only partly ionizaed in the solution.

In aqueous solution an acid undergoes ionization. The ionization of an acid is can be expressed in terms of equilibrium constant. The quantitative measurement tells about the strength of the acid. Higher the value of ${\text{K}}_a$ stronger will be the acid. The acid dissocition can be represented as following equilibrium,

${\text{HA }}_{\left(\text{aq}\text{.}\right)}{\text{+ H}}_{\text{2}}{\text{O}}_{\left(l\right)}\rightleftharpoons {\text{ H}}_{\text{3}}{\text{O}}^{+}{}_{\left(\text{aq}\text{.}\right)}{\text{+ A}}^{-1}{}_{\left(\text{aq}\text{.}\right)}$

The dissociation constant for the acid is ${\text{K}}_a$,

${\text{K}}_a=\frac{\left[{\text{H}}_{\text{3}}{\text{O}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$

For simplifications ${\text{pK}}_a$ value is used to find the acidic strength. Which is calculated by taking negative logarithm of ${\text{K}}_a$.

${\text{pK}}_a=-\log \left({\text{K}}_a\right)$

pKa: It is introduced as an index to express the acidity of weak acids, where $p{K}_{\text{a}}$ is defined as fallows, we consider the $K_{\text{a}}$ constant for acetic acid $1.8\times {10}^{-5}(pKa)$ but $p{K}_{\text{a}}$ constant for is 4.8 which is a simpler expression. Furthermore the smaller pKa value has strongest acid.