In Figure 19.1 the equivalence point is at point D. If 40.00 mL of C = 0.106 for

Question

In Figure 19.1 the equivalence point is at point D. If 40.00 mL of C = 0.106 formic acid(HOOCH) is titrated with 0.212 M NaOH, what is the volume of titrant, NaOH, required to reach the equivalence point D. At point D., the titrated solution is basic. Show reaction that is responsible for the basic pH at the equivalence point D Using the Ka for formic acid, calculate the pH at the equivalence point D. for the titration described in Question 1. Calculate the pi I at the beginning of a titration of 50.00 of 0.005M HA (Ka = 2.0 times 10^-2) with NaOH solution. If the quadratic equation is assumed to be accurate, what would the percent error in the pH if the simpler (squareroot) equation were used to calculate the pH instead. According to Figure 19.1 at which points A.B.C. D. on the titration curve does a buffer solution result?

Explanation / Answer

Q1.

a)

V = 40 mL, M = 0.106 M of acid

M = 0.212 M; V = ?

find voluem required

1:1 ratio so

mol of acid = mol of base

M1*V1 = M2*V2

40*0.106 = 0.212*V2

V2 = 40*0.106/0.212

V2 = 20 mL of BASE

1b)

the reaction responsible for basic pH:

HCOOH --> HCOO-

HCOO-(aq) + H2O(l) --> HCOOH(aq) + OH-(aq)

Q2.

use Ka for pH:

Kb = [HCOOH][OH-]/[HCOO-]

(10^-14)/(1.8*10^-4) = 5.55*10^-11

5.55*10^-11 = x*x/(40*(0.106)/100 -x)

5.55*10^-11 = x*x/(0.0424 -x)

x = OH- = 1.53*10^-6

pOH = -log( 1.53*10^-6) = 5.81530

ph = 14-5.81530 = 8.1847

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