Why is the formula pH=(1/2)(pKa1+pKa2) used?
Moderators: Chem_Mod, Chem_Admin
-
Chem_Mod
- Posts: 23858
- Joined: Thu Aug 04, 2011 1:53 pm
- Has upvoted: 1253 times
-
Chem_Mod
- Posts: 23858
- Joined: Thu Aug 04, 2011 1:53 pm
- Has upvoted: 1253 times
Re: Why is the formula pH=(1/2)(pKa1+pKa2) used?
The formula is used when a polyprotic compound is amphiprotic (it acts as both an acid and a base). Because it can behave as both, it is not obvious if the pH will be acidic or basic. Noting that a high pKa means a small Ka value, having both high pKa1 and pKa2 values tells you that the polyprotic compound doesn't behave as a good acid, so we expect a higher pH, which is what the formula pH=(1/2)(pKa1+pKa2) tells us as well.
Return to “Amphoteric Compounds”
Who is online
Users browsing this forum: No registered users and 12 guests