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Multiple Choice
Calculate the pH of a solution that is 0.075 M in HNO₃ and 0.170 M in HC₇H₅O₂, given that HNO₃ is a strong acid and HC₇H₅O₂ is a weak acid.
A
pH = 2.45
B
pH = 4.89
C
pH = 3.67
D
pH = 1.12
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1
Identify the nature of the acids: HNO₃ is a strong acid, meaning it completely dissociates in water, while HC₇H₅O₂ is a weak acid, meaning it only partially dissociates.
Calculate the concentration of hydrogen ions [H⁺] contributed by the strong acid HNO₃. Since it is a strong acid, the concentration of H⁺ ions is equal to the concentration of the acid: [H⁺] = 0.075 M.
Consider the contribution of hydrogen ions from the weak acid HC₇H₅O₂. However, since HNO₃ is a strong acid and its contribution to [H⁺] is significant, the contribution from HC₇H₅O₂ can be considered negligible for the pH calculation.
Calculate the pH of the solution using the formula: pH = -log[H⁺]. Substitute the concentration of hydrogen ions from the strong acid into the formula.
Evaluate the expression to find the pH of the solution. Since the contribution from the weak acid is negligible, the pH is primarily determined by the strong acid HNO₃.