Which of the solutions below will have the lowest pH? 0.10 M HBr 0.10 M HF 0.25 M HC2H3O2 View Available Hint(s) Which of the solutions below will have the lowest pH? 0.10 M HBr 0.10 M HF 0.25 M HC2H3O2 0.10 M HF 0.10 M HBr 0.25 M HC2H3O2 0.10 M HBr and 0.10 M HF will have the same (lowest) pH.
The Correct Answer and Explanation is:
To determine which solution will have the lowest pH, we need to understand the nature of the acids involved and their dissociation properties.
1. 0.10 M HBr (Hydrobromic acid):
HBr is a strong acid, meaning it completely dissociates in water: HBr→H++Br−\text{HBr} \rightarrow \text{H}^+ + \text{Br}^-HBr→H++Br−
Since it dissociates completely, the concentration of hydrogen ions [H+][H^+][H+] will be equal to the molarity of the acid, i.e., 0.10 M. The pH of a strong acid solution is calculated as: pH=−log[H+]\text{pH} = -\log[H^+]pH=−log[H+]
For HBr, we have: pH=−log(0.10)=1.00\text{pH} = -\log(0.10) = 1.00pH=−log(0.10)=1.00
2. 0.10 M HF (Hydrofluoric acid):
HF is a weak acid, meaning it does not dissociate completely in water. The dissociation reaction for HF is: HF⇌H++F−\text{HF} \rightleftharpoons \text{H}^+ + \text{F}^-HF⇌H++F−
The degree of dissociation is represented by the acid dissociation constant KaK_aKa. The value for KaK_aKa of HF is 7.2×10−47.2 \times 10^{-4}7.2×10−4, indicating that it dissociates only partially. To calculate the pH, we would need to use the equilibrium expression for the dissociation of HF, but since it doesn’t dissociate fully, the concentration of [H+][H^+][H+] will be less than 0.10 M, resulting in a higher pH compared to HBr.
3. 0.25 M HC₂H₃O₂ (Acetic acid):
Acetic acid is also a weak acid, and its dissociation constant KaK_aKa is 1.8×10−51.8 \times 10^{-5}1.8×10−5. Like HF, it dissociates only partially. The concentration of [H+][H^+][H+] in this solution will also be less than the initial concentration of 0.25 M, leading to a pH that is higher than that of HBr but still less than neutral.
Comparison of pH:
- 0.10 M HBr will have the lowest pH because it is a strong acid that dissociates completely, giving a high concentration of hydrogen ions.
- 0.10 M HF and 0.25 M HC₂H₃O₂ will both have higher pH values than HBr, as they are weak acids that dissociate partially.
Thus, the solution with the lowest pH is the 0.10 M HBr, as it is a strong acid and dissociates completely, providing the highest concentration of hydrogen ions.
Conclusion:
The solution with the lowest pH is 0.10 M HBr.
