Question

The \([OH^-]\) in a solution is \(1 \times 10^{-12}\) mol dm\(^{-3}\). What is the concentration of \(H^+\) ions?

• A. 0.1 mol dm\(^{-3}\)
• B. 1.0 mol dm\(^{-3}\)
• C. 2.0 mol dm\(^{-3}\)
• D. 0.01 mol dm\(^{-3}\)

Hint:

For aqueous solutions at 25°C, \([H^+][OH^-] = 10^{-14}\). If one is known, the other is \(10^{-14}\) divided by it.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We are given hydroxide ion concentration \([OH^-] = 1 \times 10^{-12}\) mol dm\(^{-3}\) and need to find \([H^+]\).

Step 2: Key Formula or Approach:
At 25°C, the ionic product of water is \(K_w = [H^+][OH^-] = 1 \times 10^{-14}\).

Step 3: Detailed Explanation:
\[ [H^+] = \frac{K_w}{[OH^-]} = \frac{1 \times 10^{-14}}{1 \times 10^{-12}} = 1 \times 10^{-2} = 0.01 \text{ mol dm}^{-3}. \]

Step 4: Final Answer:
The concentration of \(H^+\) ions is 0.01 mol dm\(^{-3}\), option (D).