Question

A monoprotic acid in $1.00M$ solution is \[0.01\% \]ionized. The dissociation of this acid is?
A) \[1 \times {10^{ - 8}}\]
B) \[1 \times {10^{ - 4}}\]
C) \[1 \times {10^{ - 6}}\]
D) \[1 \times {10^{ - 5}}\]

Answer 1

Hint: We need to remember that monoprotic acids are a type of acids that are able to donate only one proton. They follow the Bronsted Lowry theory of acid base proton donation and acceptance. A monoprotic acid can be identified by the presence of an equivalence point in a titration curve.

Complete answer:
We need to know that hydrogen bromide is a monoprotic acid that's considered to be a strong acid because it readily loses its hydrogen ion in solution. Acids that do not readily lose their hydrogens in solution are considered to be weak acids. The dissociation constant for the given monoprotic acid is \[{10^{ - 8}}\]
Dissociation of a monoprotic acid 'HX' is given by the equation:
\[HX\underset {} \leftrightarrows {H^ + } + {X^ - }\]
At $\begin{array}{*{20}{c}}
  {t = 0}&c&0&0
\end{array}$
At $\begin{array}{*{20}{c}}
  {t = teq}&{c - c\alpha }&{c\alpha }&{c\alpha }
\end{array}$
Dissociation constant, \[{k_a}\] is given by:
\[{k_a} = \dfrac{{[{H^ + }][{X^ - }]}}{{[HX]}}\]
\[{k_a} = \dfrac{{(c\alpha )(c\alpha )}}{{c - c\alpha }}\]
\[{k_a} = \dfrac{{c{\alpha ^2}}}{{1 - \alpha }}\]
Here, $c = 1M$
\[\alpha = 0.01\% = 0.0001 = {10^{ - 4}}\]
As \[\alpha < < 1;(1 - \alpha ) = 1\]
Putting values in the above equation, we get:
\[{k_a} = \dfrac{{1 \times {{({{10}^{ - 4}})}^2}}}{1}\]
On simplification we get,
\[{k_a} = {10^{ - 8}}\]
According to Brønsted and Lowry an acid is a proton donor and a base is a proton acceptor. This idea of proton donor and proton acceptor is important in understanding monoprotic and polyprotic acids and bases because monoprotic corresponds to the transfer of one proton and polyprotic refers to the transfer of more than one proton. One way to display the differences between monoprotic and polyprotic acids and bases is through titration, which clearly depicts the equivalence points and acid or base dissociation constants.

Note:
We have to remember that a monoprotic acid is an acid that can donate only one proton, while polyprotic acid can donate more than one proton. Similarly, a monoprotic base can only accept one proton, while a polyprotic base can accept more than one proton.