Formic acid (HCOOH) is an acid produced by some stinging insects (e.g., fire ant
ID: 964613 • Letter: F
Question
Formic acid (HCOOH) is an acid produced by some stinging insects (e.g., fire ants) and plants such as stinging nettles. A student working on a research project obtains a 50.00mL formic solution extracted from stinging nettles and titrates the solution with 12.50mL of a 0.100M NaOH solution. Constants needed are in the data table. From the titration data, what is the concentration of Formic acid (FA) in the solution? What is the PH after the student has added 6.25 mL of the NaOH solution? Calculate the PH at the equivalence point.Explanation / Answer
a) millimoles of acid = millimoles of base
50 x C = 12.50 x 0.100
C = 0.025 M
concentration of formic acid = 0.025 M
b)
millimoles of acid = 0.025 x 50 = 1.25
millimoles of base = 0.1 x 6.25 = 0.625
HCOOH + NaOH ------------------> HCOONa + H2O
1.25 0.625 0 0
0.625 0 0.625 -
it is half equivalence point here pH = pKa
pKa = 3.74
pH = 3.74
c)
at equivalence point only salt remains ;
salt concentration = 1.25 / (12.50 +50)
= 0.02 M
pH = 7 + 1/2 [pKa + logC]
pH = 7 + 1/2 [3.74 + log 0.02]
pH = 8.02