Acid strength-HClO4 vs H3PO4 (HW 12.51d)

Moderators: Chem_Mod, Chem_Admin

Izzy Ick 4B
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Acid strength-HClO4 vs H3PO4 (HW 12.51d)

Postby Izzy Ick 4B » Sun Nov 29, 2015 8:59 pm

HW 12.51 part d

When you compare acids like HClO4 and H3PO4 that differ in multiple ways (number of H atoms, Cl v. P), how do you determine which one is stronger?

Jonathan Shih 3H
Posts: 37
Joined: Fri Sep 25, 2015 3:00 am

Re: Acid strength-HClO4 vs H3PO4 (HW 12.51d)

Postby Jonathan Shih 3H » Mon Nov 30, 2015 3:11 am

In this case, I think you just have to know that perchloric acid is a strong acid so it dissociates completely in an aqueous solution while phosporic acid simply does not as it is a weak acid. Sorry if I can't come up with a better explanation but I think this one of those more black and white answers where you just have to memorize the list of strong acids!
Hope I helped!

Chem_Mod
Posts: 18400
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 435 times

Re: Acid strength-HClO4 vs H3PO4 (HW 12.51d)

Postby Chem_Mod » Tue Dec 01, 2015 11:23 am

To approach this problem, we should look at the similarities of the polyatomic ions: there is one central atom (phosphorus/chlorine) and 4 surrounding oxygen atoms to which hydrogen atoms will attach. Chlorine has a higher electronegativity than phosphorus, so it pulls the oxygen atom electrons towards itself with greater force than phosphorus. The fact that chlorine has a higher pull means that oxygen electrons become less accessible for the hydrogen atoms to "share", making it less favorable for hydrogen to stay bonded versus dissociating from the acid. Phosphorus by contrast pulls the electrons less, meaning that hydrogen has greater access to oxygen electrons, making it less favorable for it to dissociate, hence why H3PO4 is a weaker acid.


Return to “Properties & Structures of Inorganic & Organic Acids”

Who is online

Users browsing this forum: No registered users and 0 guests