Question

Calculate the \([\text{H}_3\text{O}^+]\) if pH of the solution is \(4.25\)

• A. \(6.123\times 10^{-5}\) M
• B. \(5.623\times 10^{-5}\) M
• C. \(4.508\times 10^{-5}\) M
• D. \(4.085\times 10^{-5}\) M

Hint:

Use [H3O+] = 10^(-pH).

Answer 1

The Correct Option is B

Step 1: Idea
The pH of 4.25 lies between 4 and 5, so the concentration lies between $10^{-5}$ and $10^{-4}$ M, closer to $10^{-5}$.

Step 2: Antilog
Write 4.25 as $5 - 0.75$. Then $[\text{H}_3\text{O}^+] = 10^{-5}\times 10^{0.75}$ and the antilog of 0.75 is 5.623.

Step 3: Verify
Take the log of the result: $\log(5.623\times10^{-5}) = 0.75 - 5 = -4.25$. So the pH is 4.25 as needed.

Step 4: Conclusion
Hence the answer is 5.623e-5 M. The remaining values differ in the leading digits and give pH values away from 4.25.

Final Answer:
The concentration is 5.623 x 10^-5 M. This is option (B). \[ \boxed{\text{(B) }5.623 \times 10^{-5}\ \text{M}} \]