Question

The pH of a solution is 3. What is the concentration of hydrogen ions in this solution?

• A. 1 × 10$^{-3}$ M
• B. 3 × 10$^{-4}$ M
• C. 10$^{-3}$ M
• D. 10$^{-3}$ M

Hint:

pH is a logarithmic scale where pH = $-\log_{10} [H^+]$.
A pH of 3 corresponds to $[H^+]$ = 10$^{-3}$ M.
Always check the exponent and coefficient in options.

Answer 1

The Correct Option is C

To determine the hydrogen ion concentration \([H^+]\) from a solution's pH, use the formula: \[ \text{pH} = -\log_{10} [H^+] \] Step 1: Utilize the pH formula
Given pH = 3, rearrange the formula to solve for \([H^+]\):
\[ [H^+] = 10^{-\text{pH}} \] Step 2: Input the pH value
Substitute pH = 3 into the equation:
\[ [H^+] = 10^{-3} \, \text{M} \] Step 3: Interpret the result
The hydrogen ion concentration is \( 10^{-3} \, \text{M} \),
which equals 0.001 moles per liter.
Step 4: Evaluate the options
- (a) 1 × 10$^{-3}$ M is equivalent to 10$^{-3}$ M.
- (b) 3 × 10$^{-4}$ M is not equivalent.
- (c) 10$^{-3}$ M matches the calculated value.
- (d) 10$^{-3}$ M is a repeat of (c).
Options (a) and (c) are equivalent; however, (c) follows standard notation.
Step 5: Conclusion
The hydrogen ion concentration is \( 10^{-3} \, \text{M} \),
making (c) 10$^{-3}$ M the correct selection.