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# pH Calculation

The pH is the negative logarithm of the hydrogen ion concentration

pH CALCULATION

The pH is the negative logarithm of the hydrogen ion concentration

pH = –log10 [H+]

Example: Calculate the pH of 0.01 M HNO3?

### Solution:

[H+] = 0.01

pH = –log10 [H+]

pH = –log10 [0.01]

pH = –log10 [1 × 102]

pH = –(log101 – 2 log1010)

pH = 0 + 2 × log1010

pH = 0 + 2 × 1 = 2

pH = 2

pOH: The pOH of an aqueous solution is realted to the pH.

The pOH is the negative logarithm of the hydroxyl ion concentration

pOH = –log10[OH]

### Example:

The hydroxyl ion concentration of a solution is 1 × 109M. What is the pOH of the solution?

### Solution

pOH = –log10 [OH]

pOH = –log10 [1 × 109]

pOH = –(log10 1.0 + log10 109)

pOH = –(0–9 log1010)

pOH = –(0 – 9)

pOH = 9

## Relationship between pH and pOH

The pH and pOH of a water solution at 25oC are related by the following equation.

pH + pOH = 14

If either the pH or the pOH of a solution is known, the other value can be calculated.

Example: A solution has a pOH of 11.76.

What is the pH of this solution?

pH = 14 – pOH

pH = 14 – 11.76 = 2.24

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10th Science : Chapter 10 : Types of Chemical Reactions : pH Calculation |