What is the pH of a solution if the concentration of hydrogen ions [H⁺] is 1 x 10⁻⁷ M?

• A. 6
• B. 7
• C. 8
• D. 9

Answer: (B)

The pH of a solution is calculated using the formula:

[

\text{pH} = -\log[H^{+}]

]

Given that the concentration of hydrogen ions ([H^+]) is (1 \times 10^{-7} , M), we can substitute this value into the formula:

[

\text{pH} = -\log(1 \times 10^{-7})

]

Using the properties of logarithms, this simplifies to:

[

\text{pH} = 7

]

This indicates that a solution with a hydrogen ion concentration of (1 \times 10^{-7} , M) is neutral, as a pH of 7 corresponds to pure water at 25°C.

In the context of the pH scale, values below 7 indicate acidity while values above 7 indicate basicity. Therefore, since the calculated pH is exactly 7, it confirms the solution is neither acidic nor basic but neutral. Understanding this is crucial for assessing the nature of various solutions in chemical and biological contexts.