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 find the concentration of hydrogen ions \([H^+]\) given the pH of the solution,
we use the pH formula: 
\[ \text{pH} = -\log_{10} [H^+] \] Step 1: Use the pH formula 
The pH is given as 3. Rearrange the formula to solve for \([H^+]\): 
\[ [H^+] = 10^{-\text{pH}} \] Step 2: Substitute the pH value 
Substitute pH = 3 into the equation: 
\[ [H^+] = 10^{-3} \, \text{M} \] Step 3: Interpret the result 
The concentration of hydrogen ions is \( 10^{-3} \, \text{M} \), 
which is equivalent to 0.001 moles per liter. 
Step 4: Compare with options 
- (a) 1 × 10$^{-3}$ M is the same as 10$^{-3}$ M. 
- (b) 3 × 10$^{-4}$ M is different. 
- (c) 10$^{-3}$ M matches the calculated value. 
- (d) 10$^{-3}$ M is a duplicate of (c). 
Since (a) and (c) are equivalent, either is correct, but (c) aligns with standard notation. 
Step 5: Conclusion 
The concentration of hydrogen ions is \( 10^{-3} \, \text{M} \), 
making (c) 10$^{-3}$ M the correct answer.