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.