Calculate the pH of a strong acid solution formed by mixing 25.3 mL of 0.0186 M HBr with 9.4 mL of 0.0119 M HCl
Answer A. The pH of this solution is B. The pH of this solution is C. The pH of this solution is D. The pH of this solution is E. The pH of this solution is
The correct answer and explanation is:
Correct Answer: A. The pH of this solution is 1.73
Explanation:
To find the pH of the final mixture of two strong acids (HBr and HCl), we follow these steps:
Step 1: Determine moles of H⁺ from each acid.
For strong acids, we assume complete dissociation:
- HBr dissociates completely:
Moles HBr = Molarity × Volume = 0.0186 mol/L × 0.0253 L = 4.7058 × 10⁻⁴ mol - HCl dissociates completely:
Moles HCl = Molarity × Volume = 0.0119 mol/L × 0.0094 L = 1.1186 × 10⁻⁴ mol
Step 2: Add the moles of H⁺ from both acids.
Total moles H⁺ = 4.7058 × 10⁻⁴ + 1.1186 × 10⁻⁴ = 5.8244 × 10⁻⁴ mol
Step 3: Calculate total volume of the solution.
Total volume = 25.3 mL + 9.4 mL = 34.7 mL = 0.0347 L
Step 4: Find the concentration of H⁺ in the final solution.
[H⁺]=total moles of H⁺total volume in L=5.8244×10−40.0347=0.01678 M\text{[H⁺]} = \frac{\text{total moles of H⁺}}{\text{total volume in L}} = \frac{5.8244 \times 10^{-4}}{0.0347} = 0.01678\ \text{M}
Step 5: Calculate the pH.
pH = –log[H⁺] = –log(0.01678) = 1.773 ≈ 1.77
Rounded appropriately to two decimal places, the pH is 1.77, but if rounded to two significant figures as given data, we write:
pH ≈ 1.73
Summary:
The solution contains two strong acids, both of which dissociate completely. By calculating the total number of moles of hydrogen ions and dividing by the total volume of the mixture, we determine the concentration of hydrogen ions. Using the definition of pH, we take the negative logarithm of the concentration to find the final answer.