® Grad /8/2017 11:55 PM A 37.9/100 Print Calculator Q Periodic Table on 19 of 26
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® Grad /8/2017 11:55 PM A 37.9/100 Print Calculator Q Periodic Table on 19 of 26 Sapling Learning The half-equivalence point of a titration occurs half way to the end point, where half of the analyte has reacted to form its conjugate, and the other half still remains unreacted. 10.440 moles of a monoprotic weak acid (K, 3.8 * 10°) is titrated with NaC , what is the pH of the solution at the half-equivalence point? Number pH- O Previous Vam sonson e Checa Answer Onu contactius O -di -7 OPXAR 8 enw =Explanation / Answer
The Ka of weak acid is 3.8x10-5
Thus pKa of acid = 4.42
Now the titration
HA + NaOH --------------------> NaA + H2O
0.440 0 0 - initial moles
0.220 0 0.220 - at the half equivalence point
Now the solution has 0.220mol of weak acid HA and 0.220moles of its conjugate base A-
Thus the solution acts as abuffer.
The pH of a buffer is calculated using Hendersen equation
pH = pKa + log [conjugate base]/[acid]
= 4.42 + log 0.22/0.22
= 4.42
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