Question

The pH of a solution of \( 10^{-7} \, \text{M} \, \text{HCl} \) at 25°C is:

• A. 7.0
• B. 6.79
• C. 7.89
• D. 7.69

Hint:

For a \( 10^{-7} \, \text{M} \) strong acid like HCl, the pH will be 7.0 because the concentration of \( H^+ \) ions is \( 10^{-7} \, \text{M} \).

Answer 1

The Correct Option is A

For a \( 10^{-7} \, \text{M} \, \text{HCl} \) solution, we know that the concentration of hydrogen ions is equal to the concentration of HCl, because HCl is a strong acid and dissociates completely in water. At 25°C, the concentration of hydrogen ions is \( [H^+] = 10^{-7} \, \text{M} \). The pH is calculated using the formula: \[ \text{pH} = -\log[H^+] \] Substituting the value of \( [H^+] \): \[ \text{pH} = -\log(10^{-7}) = 7.0 \] Thus, the pH of the solution is 7.0. Final Answer: \[ \boxed{7.0} \]