Homework Help: Chemistry

Posted by George2 on Tuesday, May 18, 2010 at 4:37am.

4) Which of the following is the most effective buffer system for a pH value of 4.45?

a. H2CO3/HCO3- (K1 = 4.4 * 10-7)

b. HCO3-/CO32- (K2 = 4.7 * 10-11)

c. H2S/HS- (K1 = 1.0 * 10-7)

d. HC2O4-/C2O42- (K2 = 5.0 * 10-5)

e. H3PO4/H2PO4- (K1 = 7.5 * 10-3)
I think is D.
Because when i work out , i am uing
-log 5* 10-5 that is close to 4.3. Is that true Can u help me, Thanks

Chemistry - DrBob222, Tuesday, May 18, 2010 at 11:01am
That's right. You want the pKa value to be as close to the desired pH as possible. D fits the closest.

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