Titration of Na2CO3 with HCl >> Calculate Ka2 and Ka1 for Carbonic acid
In a Na2CO3 titration with HCl
I am supposed to do the following:
Calculate Ka2 (pH=pKa2 at 1/2 V equivalence point 1)
and Ka1 (pH=pKa1 at 1/2 (V ep2 - V ep1) for Carbonic acid (H2CO3).
I'm confused because of the 1/2 V eqivalence point volumes... I'm not sure how I would know what those are.
From my titration curve I know that equivalence point one is at 9.90 mL HCl and 8.11 pH and that equivalence point two is 19.4 mL and 4.32 pH,
but I don't know where to go from there.
The 1/2 V Equivalent Point 1 ( at 9.90 / 2 => 4.95 mL ) is the point where half of Carbonate ion was consumed and equal amount of Bicarbonate ion was generated. ====> [ CO3 ion ] = [ HCO3 ion ]
At this 1/2 V Equivalent Point 1 ; pH of solution will be equal to pKa2 of Carbonic acid.
The 1/2 V Equivalent Point 2 ( at 19.40 - 9.90 / 2 => 4.75 + 9.90 => 14.65 mL ) is the point where half of Bicarbonate ion was consumed and equal amount of Carbonic acid was generated. ====> [ HCO3 ion ] = [ H2CO3 ]
At this 1/2 V Equivalent Point 2 ; pH of solution will be equal to pKa1 of Carbonic acid.