TO NOTE THAT AT HALF EQUIVALENCE POINT THE CONCENTRATION OF ANION FORMED IS EQUAL TO CONCENTRATION OF THE REMAINING ACID.
HCOOH + NaOH H2O +HCOO-Na+
AT HALF EQUIVALENCE POINT [ HCOOH ] = [HCOO-Na+]
AT HALF EQUIVALENCE POINT HALF OF THE VOLUME OF SODIUM HYDROXIDE NEUTRALISES HALF OF THE ACID HCOOH, SO CONCENTRATION SALT FORMED = CONCENTRATION OF ACID REMAINING.
IN THE HENDERON EQUATION , THEN pH BECOMES EQUAL TO pKa VALUE OF HCOOH
SO pH = pKa
= -LOG(1.8X 10-4)
= 4- LOG1.8
= 4-0.25527
= 3.74
OPTION e IS MATCHING
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