Titrimetric Determination of an Equilibrium Constant
In this experiment you will determine the equilibrium constant for the esterification reaction
between n-propyl alcohol and acetic acid.
HC2H3O2
+
C3H7OH

C2H3O2C3H7
+
H2O
Acetic acid
n-propyl alcohol 
n-propyl acetate
water
Esterification reactions are typically catalyzed by the addition of a strong mineral acid. In this
experiment a small amount of sulfuric acid will be needed as a catalyst. The amount of catalyst
added will have to be determined, because this amount of catalyst will also be present in the
equilibrium mixture and will need to be subtracted from the titrimetric determination of [H+] to
avoid under estimation of the Keq.
You must set up the reaction in such a way that the initial concentrations of HC2H3O2 and
C3H7OH within the mixture are known. The reaction should then be allowed to stand for one
week to come to equilibrium. As HC2H3O2 reacts with C3H7OH, the acidity of the mixture will
decrease, reaching a constant concentration once the system reaches equilibrium. The quantity
of acid present in the equilibrium system should then be determined.
The concentration of acetic acid in the mixture is determined by the technique of titration.
Acetic acid reacts with sodium hydroxide on a 1:1 stoichiometric basis:
HC2H3O2 + NaOH  NaC2H3O2 + H2O
The concentration of n-propyl alcohol will be determined stoichiometrically from the amount of
acetic acid present. We will use volumes that allow for equal molar quantities of acetic acid and
n-propyl alcohol at the start of the reaction.
Procedural Notes:
A. First Week- Set Up of the Initial Reaction Mixture
1. Items to choose from for use during this experiment:
Graduated cylinders
volumetric pipettes
Erlenmeyer flasks
beakers
burets
buret clamps
droppers
phenolphthalein
NaOH
HC2H3O2
C3H7OH
2. Use a precisely measured quantity around 14 mL of glacial acetic acid, and around 19 mL
of n-propyl alcohol. Fill the remaining volume with water to a total solution volume of
50 mL. Swirl to mix, which will begin the reaction.
3. Initial concentration of the acetic acid should be determined before addition of the
sulfuric acid catalyst. Titrate two samples, three if it looks like there will be time.
4. 10 drops is an appropriate amount of catalyst, and will not significantly change the
volume of the solution. Do not add until after initial concentration of acetic acid has been
determined.
5. Concentration of sulfuric acid catalyst in the flask must be determined, and use of a blank
may be considered to be most accurate. Titrate two samples, three if it looks like there
will be time.
C. Second Week- Determination of the Equilibrium Mixture
1. After standing for a week, the reaction system of n-propyl alcohol and acetic acid will
have come to equilibrium.
2. Titrate two samples, three if you have time.
Elements of a Thorough Analysis (Calculations and Conclusions):
1. From the average volume of NaOH used to titrate 1.00 mL of the reaction mixture and
the concentration of the NaOH, calculate the concentration (in mol/L) of acetic acid and
the concentration (in mol/L) of n-propyl alcohol in the reaction mixture.
2. By subtracting the average volume of standard NaOH used in Part A (acetic acid only)
from the average volume of NaOH used in Part B (acetic acid + sulfuric acid), calculate
how many milliliters of the standard NaOH solution are required to titrate the sulfuric
acid catalyst present in 1 mL of the reaction mixture. This volume represents a
correction that can be applied to the volume of NaOH that will be required to titrate the
samples next week, after equilibrium has been reached.
3. Calculate the mean volume of standard NaOH required to titrate 1.00mL of the
equilibrium mixture. Using the volume of NaOH required to titrate the sulfuric acid
catalyst present in the mixture (from Part B), calculate the volume of NaOH that was
used in titrating the acetic acid component remaining in the equilibrium mixture.
4. From the volume and concentration of NaOH used to titrate the acetic acid in 1.00 mL of
the equilibrium mixture, calculate the concentration of acetic acid in the equilibrium
mixture in mol/L. Since the reaction was begun with equal molar amounts of acetic acid
and n-propyl alcohol, the concentration of n-propyl alcohol in the equilibrium mixture is
the same as that calculated for acetic acid.
5. Calculate the change in the concentration of acetic acid between the initial and the
equilibrium mixtures. Form the change in the concentration of acetic acid, calculate the
concentrations of the two products of the reaction (n-propyl acetate, water) present in the
equilibrium mixture.
6. From the concentrations of each of the four components of the system at equilibrium,
calculate the equilibrium constant for the reaction.
7. Calculate the equilibrium constant for this reaction.
8. Sulfuric acid was used as a catalyst in this reaction. Would the presence of a catalyst
affect the position of the equilibrium (ie, the relative amounts of substances present once
equilibrium was reached)? Why?