OUR LADY OF THE ROSARY COLLEGE
CHEMISTRY PRACTICAL MANUAL
 Advanced Level
 Experiment should be carried out under the supervision of a Chemistry teacher
 Full report is required.
Division of work: Two students per group
The distribution of butanedioic acid between water and ethoxyethane
Introduction
When a solute which is significantly soluble in two immiscible solvents is shaken up in the
presence of both of these solvents, it does not dissolve exclusively in the solvent in which it is most
soluble, but distributes itself between both solvents. The purpose of this experiment is to investigate
the relationship of solubility of a solute between two immiscible liquids.
Butanedioic acid, HO.CO.CH2.CH2.CO.OH is used as the solute and the immiscible solvents
are water and ethoxyethane (diethyl ether), CH3CH2.O.CH2CH3
Chemicals
Ethoxyethane (120 cm3), butanedioic acid solid (2-3 g), phenolphthalein indicator solution,
0.50 M sodium hydroxide solution (200 cm3), 0.10 M sodium hydroxide solution (200 xm3).
Additional Apparatus
Pipette filler, burette, separating funnel
Pre-laboratory work
1. What do you understand by the term immiscible liquids?
2. Define 'Partition coefficient'. Would you expect the partition coefficient to vary with
temperature?
3.
4.
5.
6.
7.
8.
Describe the use of a separating funnel for the separation of oil and water (assume that water is
denser than oil). What precautions should be noted if you shake the separating funnel (step 3)?
Explain the precautions you have mentioned in question 1.
Write an equation for the reaction between butanedioic acid and standardized sodium
hydroxide solution
In this practical, how can you determine the concentration of butanedioic acid in water layer
and in ether layer.
The volumes of water and ethoxyethane in step 1 and 2 are not very precise. However, volume
of them must be precisely measured before titration. Why?
If you have obtained one set of equilibrium concentration of the acid in both layers, can you
calculate the partition coefficient? Explain.
Procedure
1.
Using a measuring cylinder, transfer 50.0 cm3 of distilled water into a separating funnel.
2.
Weigh out a portion of butanedioic acid of mass 1.0 - 1.5 g (accuracy 0.1 g) and add this to
the separating funnel followed by about 50.0 cm3 of ethoxyethane.
3.
Shake the mixture well and continue shaking until all the acid has dissolved.
4.
Leave the separating funnel and its contents to stand for some minutes in order to allow the
layers to separate from each other.
5.
Run off the lower layer (aqueous solution) into a clean beaker. Pipette 10.0 cm3 of this
solution into a conical flask and titrate it with 0.50 M NaOH solution using phenolphthalein
as indicator. Record your results in the table below.
6.
Repeat the titration with a further 10.0 cm3 portion of the aqueous solution.
7.
Discard the boundary layer from the separating funnel and then, using a clean pipette and a
pipette-filler, transfer 10.0 cm3 of the ethereal solution into a clean conical flask.
8.
Add a small volume of distilled water and then titrate this with 0.10 M NaOH solution to a
phenolphthalein end-point, shaking thoroughly after each addition of alkali. Titrate a second
10.0 cm3 portion of the ether solution in the same way. Record your results in the following
table.
Repeat step 1 -8 to get another set of data.
Data and Results
First set
Second set
Mass of butanedioic acid + bottle (g) =
Mass of bottle (g) =
Mass of butanedioic acid (g) =
Concentration of sodium hydroxide solution (g) =
Titration data -- First set
Aqueous layer(0.5M
Ether layer(0.1M NaOH
NaOH used)
used)
Trial
1
2
Trial
1
2
3
Final burette reading (cm )
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Mean titre:
Mean titre:
Titration data -- Second set
Aqueous layer(0.5M
Ether layer(0.1M NaOH
NaOH used)
used)
Trial
1
2
Trial
1
2
3
Final burette reading (cm )
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Mean titre:
Mean titre:
Calculation
Calculate the equilibrium concentrations in each layer and. Show the steps for the first set of data
only. Copy equilibrium concentrations 1-3 group(s) of your class. Give names of the group
members. Tabulate all equilibrium concentrations.
The following questions help you to find out the partition coefficient:
1. Assuming that butanedioic acid is a dibasic acid, how many moles of the acid must there have
been in 10 cm3 of (a) the aqueous layer? (b)the ether layer?
2. What must have been the molarities of the acid solutions in both layers?
3. By using the data determine the equilibrium constant (the partition coefficient) of butanedioic
acid between water and ethoxyethane. You should note that the treatment of the data is
important, that is, will you simply calculate the partition coefficient or will you draw a graph to
show the relation between the equilibrium concentrations and then determine the partition
coefficient from the graph?
Questions for discussion
1. Would you expect this plot to go through the origin?
2. What physical significance can be found from the shape of the graph you have plotted? Can you
say something about (Discuss) the equilibrium system?
3. Another equilibrium system, the distribution of propanoic acid between water and benzene, is
also a good example to be studied. What safety precaution should be noted when we handle
benzene?
Answers for pre-laboratory work
1. (a) Turn off the stopper of the funnel. (b) Add chemicals into it. (c) Stopper the funnel. (d) Swirl
the content of the funnel for a while. (e) Take away the stopper to release the pressure. Repeat
step (c) to (e). Safety precaution: Release pressure inside the funnel occasionally and keep clear
of bare fire.
2. Ethoxyethane is very volatile and inflammable. The pressure inside the separating funnel is
increasing during swirling. Therefore, releasing pressure is a must. Vapour of ethoxyethane has a
very low ignition temperature (or flash point). If there is a flame, the mixture of ether and air
may explode.
3. HO.CO.CH2.CH2.CO.OH(aq) + 2NaOH(aq) ----> (CH2.COO-)2Na2+(aq) + 2H2O(l)
4.Concentrations of butanedioic acid in water and in ether are determined by titrating with the
standardized sodium hydroxide solution.