I need help with question #4, please. But if you are able to do number 2 and 3 j
ID: 706559 • Letter: I
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I need help with question #4, please.
But if you are able to do number 2 and 3 just so I can check my answers, that would be amazing. Thanks.
2. If you mixed 0.200 M each of NaHCO3 and H2CO3, what would be the pH of the resuting solution'? Using NaOH, if you neutralized 10% of the carbonic acid in the above solution-what would be the new pH of the resuting solution? 3. Using an unknown acid, you prepare a 0.300 M solution and neutralize half of that solution with NaOH. You find the resulting [H30+] is 2.5 x104. What is the pKa of the unknown acid? 4.Explanation / Answer
4)
the reaction between unknown acid and NaOH is 1:1 reaction
NaOH + HA -------------------> NaA + H2O
0.15 0.300 0 0 ------------------> initial
-0.15 -0.15 + 0.15 + 0.15 -----------> change
0.00 0.15 0.15 0.15 -------------> after reaction
half the HA is consumed by NaOH that means now only HA and NaA remains with equal amounts
according to buffer equation
pH = pKa + log [NaA / HA]
pH = pKa + log (0.15 / 0.15)
pH = pKa
pH = -log [H3O+]
pH = -log (2.5 x 10^-4)
pH = 3.60
pH = pKa =3.60
pKa = 3.60
note : short cut at half equivalence point always pH = pKa in case of weak monoprotic acid titration with strong base
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