Exercise 18.64 Consider the following curve (Eigure 1)for the titason of a weak

Question

Exercise 18.64 Consider the following curve (Eigure 1)for the titason of a weak base with a stong add and answer each of the 12 10 0 10 20 30 40 50 volume of acid added (ml) a O Ask me anything Part B What is the volume of added acid at the equivalence point? Express your answer using two significantfigures. My Answers Gere Up Part C Ar what volume of added acid isthe plHoalaulated by working an equilibrium problem based on the insal concentration Express your answer using one significant figure. Submit My Answers Part D

Explanation / Answer

B)

Volume of acid in equivalence point

The equivalence point is given when the pH changes dratically, since there is equivalence of base + acid

so

V = 23 mL approx, since pH drops from 10 to 2

C)

The pH is calculated via Kb, when there is NO volume added... since this will be a weak base, then we use

Kb = [BH+][OH-]/[B]

from the equilibrium

B + H2O <-> BH+ + OH-

where B is the weak base and BH* the protonated base

D)

volume when pH = 14- pKb

if pKb = 5, then pOH = 5, therefore pH = 14-pOH

meaning

pOH = pKb

the only point this is true is the HALF equivalece point

therefore

choose V = 1/2*Vequivalence, from previous point, V = 23 mL is equivalence point then

Half Equiv = 23/2 = 11.5 mL

E)

find vol of acid where pH is calcualted used the Ka of conjugate acid

This is when all base is neutralized to conjugate acid

so

V > Vequivalence

Above 23 mL will do

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