Get A+ with YaClass!
Register now to understand any school subject with ease and get great results on your exams!

Theory:

How to calculate the \(pH\) of a solution?
The \(pH\) is the negative logarithm of the hydrogen ion concentration.
 
i.e, \(pH= -log_{10}[H^+]\)
Example:
 
Calculate the \(pH\) of \(0.01\) \(M\) \(HNO_3\).
 
Solution:
 
\([H^+] = 0.01\)
\(pH = -log_{10}\) \([H^+]\)
\(pH = -log_{10}\) \([0.01]\)
\(pH = -log_{10}\) \([1\times10^{-2}]\)
\(pH = -(log_{10}·1 - 2\, log_{10}10)\)
\(pH = 0 + 2\times\,log_{10}\,10\)
\(pH = 0 + 2\times1 = 2\)
\(pH = 2\)
pOH
The \(pH\) is related to the \(pOH\) of an aqueous solution.
The \(pOH\) is the negative logarithm of the hydroxyl ion concentration.
 
\(pOH= -log_{10}[OH^-]\)
Example:
 
The hydroxyl ion concentration of a solution is \(1\times10^{-9}\) \(M\). What is the \(pOH\) of the
solution?

Solution:

\(pOH = -log_{10}[OH^-]\)
\(pOH = -log_{10}[1\times10^{-9}]\)
\(pOH = -(log_{10}\times1.0 + log_{10}\times10^{-9})\)
\(pOH = -(0 - 9\,log_{10}\,10)\)
\(pOH = -(0 - 9)\)
\(pOH = 9\)
 
Relationship between \(pH\) and \(pOH\):
 
At \(25°C\), the \(pH\) and \(pOH\) of a water solution are related by the following equation:
 
\(pH + pOH = 14\)
 
It is possible to calculate the other value if the \(pH\) or \(pOH\) of a solution is known.
 
Example:

\(pOH\) of a solution is \(11.76\). What is the \(pH\) of this solution?
\(pH = 14 - pOH\)

\(pH = 14 – 11.76 = 2.24\)
\(pH\) indicates acidity or hydrogen ion concentration, whereas \(pOH\) indicates alkalinity or hydroxide ion concentration.