Homework Help: Chemistry

Posted by Shaun on Wednesday, July 6, 2011 at 11:13am.

If a liter of a buffer is prepared with a final concentration of .3M monosodium phosphate and .5M disodium phosphate, what is the pH of this buffer? (Hint: Which is conjugate acid (HA) and conjugate base (A-)? What's the pKa for this particular pair of HA and A-?)

So I think the conjugate base HA is disodium phosphate and the conjugate acid A- is monosodium phosphate. Otherwise I'm not sure where to start and I'm not sure why or how I determine that at this point.

Chemistry - DrBob222, Wednesday, July 6, 2011 at 12:48pm
You want to use the Henderson-Hasselbalch equation. Substitute into
pH = pKa + log[(base)/(acid)].
The base is Na2HPO4. The acid is NaH2PO4.
Chemistry - Shaun, Wednesday, July 6, 2011 at 12:54pm
Okay, so based on the chart in my book I was able to determine the following.

pH=(unknown)
pKa=7.2 of Phosphoric Acid (2)
A-=.5M of Na2HPO4
HA=.3M H2PO4-
pH= 7.2 + log(.5/.3)
pH=7.2+log(1.6667)
pH=7.2+0.5108

So, the pH of this solution is:
pH=7.7108

Correct?
Chemistry - DrBob222, Wednesday, July 6, 2011 at 1:06pm
pH=(unknown)
pKa=7.2 of Phosphoric Acid (2)
A-=.5M of Na2HPO4
HA=.3M H2PO4-
pH= 7.2 + log(.5/.3)
pH=7.2+log(1.6667)
You are ok to here
pH=7.2+0.5108
I find 0.22 for the log of 1.6667
Chemistry - Shaun, Wednesday, July 6, 2011 at 1:48pm
Upon recalculating this you are definitely correct...log(1.6667)=0.22
so 7.2+.22=7.42
and the pH is then 7.42
Thanks again for your help.

Answer this Question

Related Questions

Chemistry - A buffer prepared by mixing equal amounts of the salts Na2HPo4 and ...
Chemistry - A buffer prepared by mixing equal amounts of the salts Na2HPo4 and ...
Chemistry - Which of the following will buffer near pH=9? a. 0.5M sodiumacetate/...
chemistry - a ferric phosphate solution is prepared by adding 2.4 g of ferric ...
Chemistry ...ASAP please - a ferric phosphate solution is prepared by adding 2.4...
biochem - I have 0.500ml of 3M ethanol and then I take 0.250ml of it and put it ...
chemistry - Calculate the mass of salts needed for constructing a buffer using ...
Chemistry(Please check answers) - 1)What is the pH of a saturated solution of ...
Chemistry - Which of the following is the most effective buffer system for a pH ...
chemistry! URGENT - A standard solution is prepared for the analysis of ...

For Further Reading

First Name:
School Subject:
Answer: