Which solution will have the lowest pH?
a. 0.10 M HClO2, pKa = 1.96
b. 0.10 M HCN, pKa = 9.21
c. 0.10 M HF, pKa = 3.19
d. 0.10 M HClO, pKa = 7.538
e. 0.00010 M HCl
Does the lower the pka stronger the acid, means the lower the ph, so the answer is A?
Yes but you must account for HCl separately. Of the acids listed with a pKa value, HClO2 is the strongest. Then HCl has pH of 4 so A is correct.
To determine which solution will have the lowest pH, we need to compare the pKa values of each compound given. The pKa value represents the acidity of a compound, with lower values indicating stronger acids.
However, it's important to note that pKa alone doesn't directly determine the pH of a solution. pH is a measure of the concentration of hydrogen ions (H+) in a solution, and it is calculated using the formula:
pH = -log[H+]
From the options provided, we can make the following comparisons:
a. 0.10 M HClO2, pKa = 1.96
b. 0.10 M HCN, pKa = 9.21
c. 0.10 M HF, pKa = 3.19
d. 0.10 M HClO, pKa = 7.538
e. 0.00010 M HCl
Comparing the pKa values, we see that HCN has the highest pKa value of 9.21, indicating that it is the weakest acid among the options. HClO2 has the lowest pKa value of 1.96, suggesting it is the strongest acid.
However, to determine the actual pH, we need to consider the concentration of each compound. While HClO2 has the lowest pKa, its concentration is the same as the other options, 0.10 M. To find the lowest pH, we need to consider the concentration of hydrogen ions (H+) present in the solution.
To compare the pH, we need to first determine the concentration of H+ for each compound. This can be done by considering the dissociation of the acid. Strong acids dissociate completely in water, while weak acids only partially dissociate.
For HClO2 (option a), since it is a strong acid, it will dissociate completely. Therefore, the concentration of H+ is 0.10 M.
For HCN (option b) and HF (option c), they are weak acids that only partially dissociate. So, to determine the concentration of H+ in their solutions, we need to calculate it using the acid dissociation constant (Ka):
[H+][A-] / [HA] = Ka
Given that the concentration of each compound is 0.10 M, we can assume that the concentration of the undissociated acid (HA) remains nearly constant. So, the concentration of H+ will be determined by the ratio of the dissociated ions (H+) to the initial concentration of the acid (HA). Comparing the pKa values, HF with a pKa value of 3.19 will have a lower concentration of H+ compared to HCN, which has a pKa of 9.21.
For HClO (option d), it is an oxyacid, which can partially dissociate to release H+. However, without further information on its dissociation constant, we cannot determine its specific concentration of H+ compared to the other options.
Lastly, for HCl (option e), since it is a strong acid, it will dissociate completely. Therefore, the concentration of H+ is 0.00010 M.
Considering the calculations above, the solution with the lowest pH would be option e, 0.00010 M HCl, as it has the lowest concentration of H+ ions.