- Joined
- Feb 10, 2011
- Messages
- 895
- Reaction score
- 126
Given that the pKa for nitrous acid is 3.34, what is the pH of a 0.10 nitrous acid solution?
A. 1.00
B. 2.17
C. 3.24
D. 4.34
If it were a strong acid, pH = - log [H+] where [H+] = .10 b.c all of the acid dissolves.
Since nitrous acid is weak acid, HA <--> H+ + A, not all of HA is converted into H+ so the pH will be more basic than pH of 1. This rules out A.
Now, since pKa is when half of the acid has been dissolved. Meaning that HA <---> H+ and A- , where [HA] = H+ and [A-]
Initially , half of the acid hasn't been dissolved, as it's a weak acid and we haven't added any titrant (to cause the reaction to shift towards dissociation and increase [H+] ...currently very little H+ , so wouldn't the answer be D?
It's not. Tell me what's the missing gap in this reasoning.
Thanks!
A. 1.00
B. 2.17
C. 3.24
D. 4.34
If it were a strong acid, pH = - log [H+] where [H+] = .10 b.c all of the acid dissolves.
Since nitrous acid is weak acid, HA <--> H+ + A, not all of HA is converted into H+ so the pH will be more basic than pH of 1. This rules out A.
Now, since pKa is when half of the acid has been dissolved. Meaning that HA <---> H+ and A- , where [HA] = H+ and [A-]
Initially , half of the acid hasn't been dissolved, as it's a weak acid and we haven't added any titrant (to cause the reaction to shift towards dissociation and increase [H+] ...currently very little H+ , so wouldn't the answer be D?
It's not. Tell me what's the missing gap in this reasoning.
Thanks!