Question

The concentration of hydrogen ions in a sample of soft drink is \[3.8 \times {10^{ - 3}}M\]. What is its pH? :-

Answer 1

Hint: Using the equation, \[pH = - \log \left[ {{H^ + }} \right]\], we can solve for pH of the solution sample as, \[ \Rightarrow \;pH = - {\log _{10}}\left[ {{H^ + }} \right]\] or, we can also write,
\[\left[ {{H^ + }} \right] = 10 - pH.\]
by exponentiating both sides with base 10 to "undo" the common logarithm. The pH of Solution can be calculated easily and we can easily get our final result.
\[ \Rightarrow \;pH + pOH = 14\]

Complete step by step answer:
In the above question, concentration of hydrogen ion in a sample of soft drink is given to be \[3.8 \times {10^{ - 3}}\]M, we have to find the pH of the solution;
First, let’s know what the pH of a solution means.
The pH of a solution is a measure of the molar concentration of hydrogen ions in the solution and as such is a measure of the acidity or basicity of the solution.
The pH scale is said to range from 0 to 14, Anything below 7.0 is acidic, and anything above 7.0 is alkaline or basic.
If the pH is about 7, the solution is neutral.
pH is defined as : \[ - {\log _{10}}\;of\;\left[ {{H^ + }} \right]\]
\[pH = - {\log _{10}}\left[ {{H^ + }} \right]\]
\[So,\;pH = - {\log _{10}} \times 3.8 \times {10^{ - 3}}\]
\[ = - (3){\log _{10}} - \log 3.8\]
\[As\;{\log _{10}}\;is\;1\;we\;get;\]
\[pH = - ( - 3) \times 1 - \log \left( {3.8} \right)\]
\[ = \left( {3 \times 1} \right) - \log \left( {3.8} \right)\] \[\left[ {\because \;\;\log \left( {3.8 = 0.57\% } \right)} \right]\]
\[ = 3 - 0.5798\]
\[ \Rightarrow \;pH = 2.42\]
\[\therefore \] pH of the solution is 2.42

Note:
The letters pH stand for potential of hydrogen, since pH is effectively a measure of the concentration of hydrogen ions (that is, protons) in a substance.
The pH scale is a measure of the acidity or alkalinity (basicity) or a solution. The scale runs from 0 to 14, with acids having a pH less than 7, 7 being neutral, and bases having a pH higher than 7. Acids and bases react with each other in what is called a neutralization reaction.