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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: penguin_nguyen on October 12, 2011, 03:54:37 AM

Title: buffer capacity of Na3PO4 and HCl solution
Post by: penguin_nguyen on October 12, 2011, 03:54:37 AM
First, I'm sorry because I'm not a foreign student my english is not good
I have a big problem with this exercise when i study analytical chemistry. Could you help me?
The concentration of HCl solution when mixed 150ml that solution with 100 mL Na3PO4 0,2M to get a pH of 7.21. The buffering capacity of the solution
H3PO4 pka1=2,15   ;  pka2 = 7,21;   pka3 = 12,32
I don't know which reactions happen when we put HCl into Na3PO4
Title: Re: buffer capacity of Na3PO4 and HCl solution
Post by: AWK on October 12, 2011, 08:59:17 AM
Hcl is a strong acid, PO43- and HPO4- are weak bases. What will happen when you mix acid with base?
Title: Re: buffer capacity of Na3PO4 and HCl solution
Post by: penguin_nguyen on October 13, 2011, 03:28:02 AM
I'm not sure.I think that may be there are two reactions.
  Na2HPO4 ----> 2Na+ +  HPO4(2-)  and    HPO4(2-)  +  H3PO4 ---->  2H2PO4-
Can you help me!?
Title: Re: buffer capacity of Na3PO4 and HCl solution
Post by: Borek on October 13, 2011, 07:20:46 AM
Neither of the reactions you wrote contains PO43- as a reactant. You are looking for

PO43- + H+ -> ...