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Nitric acid (HNO₃) is a strong acid, which means it completely ionizes in water. For a strong acid, the concentration of hydrogen ions [H⁺] is equal to the concentration of the acid. In this case, the solution has a concentration of 0.001 M, so [H⁺] = 0.001 M.
The pH of a solution is calculated using the formula:
pH = –log[H⁺]
Substitute the hydrogen ion concentration:
pH = –log(0.001)
0.001 can be written as 10⁻³. Therefore:
pH = –log(10⁻³) = 3
This shows that a 0.001 M solution of HNO₃ has a pH of 3. The pH scale ranges from 0 to 14, with values less than 7 indicating acidic solutions. Strong acids, even at low concentrations, give pH values below 7. Nitric acid, being a strong monoprotic acid, dissociates completely to produce H⁺ ions, which directly determine the pH.
Understanding the relationship between acid concentration and pH is essential in analytical chemistry. It helps in titrations, buffer preparation, and chemical analysis. Using the logarithmic formula ensures precise calculation for any molar concentration of strong acids.
0.001 M HNO₃ is an example of a dilute acid solution where pH is above 0 but still acidic. This method applies to other strong acids such as HCl, H₂SO₄ (for the first ionization), and HClO₄.
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