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Homework Help
Chem help: Buffers and pH calculations....
By dancer_all_daymember has saluted, click to view salute photos Comments: 2326, member since Thu Feb 12, 2004
On Mon Sep 24, 2012 06:31 PM

I mixed 50 mL of 0.1 M sodium dihydrogen phosphate (NaH2PO4) and 0.1 M disodium hydrogen phosphate (Na2HPO4) to make a buffer solution.

My teacher asked if the volume would go down and why? I didnt see it go down (below 100 mL) but I have a feeling volume decreases but I dont know why. Might it have something to do with more bonds being formed when the acid and base mix?

Then I placed 25 mL of the buffer solution in another beaker with 1 mL of 0.1 M NaOH. How do you calculate the pH of this new solution?

And lastly, I have to calculate the mol of A- (which herer is the HPO4 2- molecule). HE gives a hint saying that "remeber the initial solution contained half A- and half HA." Im pretty sure the Henderson-Hasselbach has to be used but how do you calculate the concentrations of acid and base??

Thanks in advance!!!!