solving for pH with diprotic/triprotic acids


by dnt
Tags: acids, solving
dnt
dnt is offline
#1
Apr20-06, 11:13 AM
P: 238
i know if you have an acid, say .0001 M HCl, to get the pH you simply take the -log of the acid concentration (which is the same as [H+]), but what if you have a diprotic (H2SO4) or triprotic (H3PO4) acid...do you need to multiply the acid contentration by 2 or 3 to get the new H+ concentration BEFORE plugging it into -log[H+]?

and the same goes for pOH? eg. Mg(OH)2 needs to be multiplied by 2?
Phys.Org News Partner Science news on Phys.org
Simplicity is key to co-operative robots
Chemical vapor deposition used to grow atomic layer materials on top of each other
Earliest ancestor of land herbivores discovered
siddharth
siddharth is offline
#2
Apr20-06, 12:22 PM
HW Helper
PF Gold
siddharth's Avatar
P: 1,198
Check out these links. They should help in answering your question.

http://www.science.uwaterloo.ca/~cch.../polyprot.html
http://www.sparknotes.com/chemistry/.../section1.html
PPonte
#3
Apr20-06, 01:03 PM
P: n/a
Mg(OH)2 do not completely ionise in water as do for instance NaOH or KOH.

Borek
Borek is online now
#4
Apr20-06, 06:22 PM
Admin
Borek's Avatar
P: 22,662

solving for pH with diprotic/triprotic acids


Depending on your level of education - you may either calculate pH assuming full dissociation, or you may need to calculate dissociation equilibrium. Check out these links: general method for polyprotic acids and bases pH calculation and simplified method of pH calculation for polyprotic substances.

Best,
Borek


Register to reply

Related Discussions
calculating molecular mass of oxalic acid (diprotic acid) using only given #s? Biology, Chemistry & Other Homework 1
triprotic acid? Chemistry 12
pH with 2 acids Biology, Chemistry & Other Homework 5
Acids and pH Biology, Chemistry & Other Homework 3
for acids Introductory Physics Homework 1