what is the pH of an aqueous nitric acid HNO3 solution that has a concentration of 0.500 M? Nitric acid is a strong acid and its dissociation in water can be respresented by the following equation: HNO3 + H2O –> H3O+ + NO3-
The Correct Answer and Explanation is:
Correct Answer:
The pH of a 0.500 M aqueous nitric acid (HNO₃) solution is 0.301.
Explanation (without using the word “we”):
Nitric acid (HNO₃) is classified as a strong acid, which means it dissociates completely in aqueous solution. This complete dissociation implies that each mole of HNO₃ produces one mole of hydronium ions (H₃O⁺). The chemical reaction in water can be expressed as:
HNO₃ + H₂O → H₃O⁺ + NO₃⁻
Given a nitric acid concentration of 0.500 M, the hydronium ion concentration in the solution is also 0.500 M because of the 1:1 molar ratio in the reaction.
The pH of a solution is determined using the formula:
pH = –log[H₃O⁺]
Substituting the known concentration:
pH = –log(0.500)
pH ≈ 0.301
This result is obtained using logarithmic rules. The negative logarithm of 0.500 gives a positive pH value, indicating an acidic solution. A pH around 0.3 is highly acidic, consistent with the behavior of strong acids at moderate concentrations.
The pH scale typically ranges from 0 to 14, with lower values corresponding to higher acidity. A pH of 0.301 confirms that the solution is strongly acidic due to the full ionization of nitric acid. This characteristic allows nitric acid to donate protons effectively and increase the hydronium ion concentration in the solution.
In summary, the pH is calculated directly from the concentration of H₃O⁺, which in the case of strong acids like HNO₃ equals the original acid concentration. Therefore, a 0.500 M solution of HNO₃ results in a pH of approximately 0.301.
