Question

What is the hydronium ion concentration of a solution whose pH is 4.12?

Answer 1

Hint: Hydronium ions, as well as hydroxide ions, as well as hydroxide ions, are found in almost all aqueous solutions. The concentration of hydronium ion is a precursor in finding out the chemical properties of the solution. The pH of a solution is defined as minus log of hydronium ion concentration.
\[\text{pH}=-\log \left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right]\]

Complete answer:
pH of a solution is the measure of its acidity or alkalinity that is calculated in terms of the concentration of hydrogen ion, hydronium ion, or hydroxide ion. A pH value of 7 is considered to be neutral where hydronium ion concentration is equal to hydroxide ion concentration. Any value below 7 or above 7 indicates that either solution is acidic or basic respectively.
The pH scale is very popularly used in chemical analysis and it is based on the p-function that is defined as below:
\[\text{pX}=-\log \left[ \text{X} \right]\]
Here X is the quantity of interest in terms of which we have to find the concentration value. In this question, our quantity of interest is hydronium ion and the negative logarithm of hydronium ion will give the pH value.
So, we can calculate hydronium ion concentration from pH value as stepwise mentioned below.
\[\begin{align}
  & \text{pH}=-\log \left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right] \\
 & \because \text{pH}=4.12 \\
 & \Rightarrow \log \left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right]=-4.12 \\
 & \Rightarrow \left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right]={{10}^{-4.12}} \\
 & \text{or }\left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right]=\text{antilog}\left( -4.12 \right) \\
 & \Rightarrow \left[ {{\text{H}}_{\text{3}}}{{\text{O}}^{+}} \right]=7.58\times {{10}^{-5}}\text{ M} \\
\end{align}\]
Hence, the hydronium ion concentration of a solution with pH 4.12 is \[7.58\times {{10}^{-5}}\text{ M}\].

Note:
The hydronium ion concentration in pure water or we can say in any neutral solution is $1.0\times {{10}^{-7}}\text{M}$ at $25{}^\circ \text{C}$ . The pH and pOH values of a neutral solution at this temperature are the same and equal to 7:
\[\text{pH}=\text{pOH}=-\log \left( 1.0\times {{10}^{-7}} \right)=7.00\]