Question

Calculate the pH of a \(0.001\,\text{M}\) solution of \(HNO_3\).

• A. \(1\)
• B. \(2\)
• C. \(3\)
• D. \(4\)

Hint:

For strong acids, assume complete dissociation. If \([H^+] = 10^{-n}\), then \(pH = n\).

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to determine the acidity of a Nitric acid solution expressed as pH. Nitric acid (\(HNO_3\)) is a strong monoprotic acid.
Step 2: Key Formula or Approach:
1. For a strong acid: \([H^+] = \text{Molarity of the acid}\) (if monoprotic).
2. \(pH = -\log_{10}[H^+]\)
Step 3: Detailed Explanation:
Since \(HNO_3\) is a strong acid, it dissociates completely:
\[ HNO_3 \rightarrow H^+ + NO_3^- \]
Given concentration \([HNO_3] = 0.001\,\text{M} = 10^{-3}\,\text{M}\).
Therefore, \([H^+] = 10^{-3}\,\text{M}\).
Calculating pH:
\[ pH = -\log(10^{-3}) \]
Using the log property \(\log(a^b) = b\log(a)\):
\[ pH = -(-3)\log(10) \]
Since \(\log(10) = 1\):
\[ pH = 3 \]
Step 4: Final Answer:
The pH of the solution is \(3\).