Question

What is the pH of a 1×10−4
mol HCl solution?(1 point)
Responses

6
6

8
8

2
2

4

Answer 1

To determine the pH of a \(1 \times 10^{-4}\) mol HCl solution, we first note that HCl is a strong acid and will dissociate completely in solution. Therefore, the concentration of hydrogen ions \([H^+]\) will also be \(1 \times 10^{-4} \, \text{M}\).

The formula for calculating pH is:

\[
\text{pH} = -\log[H^+]
\]

Substituting the value we have:

\[
\text{pH} = -\log(1 \times 10^{-4}) = 4
\]

However, we need to consider that the solution also contains a small amount of \(H^+\) ions from the water itself (from the autoionization of water). Pure water has a \([H^+]\) concentration of \(1 \times 10^{-7} \, \text{M}\). When calculating the pH of very dilute acid solutions, we must account for this contribution.

This results in the total \([H^+]\):

\[
[H^+]_{\text{total}} = 1 \times 10^{-4} + 1 \times 10^{-7} \approx 1 \times 10^{-4} \, (\text{since } 1 \times 10^{-4} \text{ is much larger than } 1 \times 10^{-7})
\]

Thus, the estimated pH remains close to 4.

Therefore, the correct answer to the pH of a \(1 \times 10^{-4}\) mol HCl solution is:

**4**