Experiment P13
To determine the partition coefficient of butanedioic acid (HO 2C(CH2)2CO2H)
between water and diethyl ether (CH 3CH2OCH2CH 3)
Chemicals:
Apparatus:
butanedioic acid
about 2.0 g
diethyl ether
40 cm3
0.50 M sodium hydroxide
about 60 cm3
0.10 M sodium hydroxide
about 45 cm3
phenolphthalein indicator
about 1 cm3
100 cm 3 separating funnel,
50 cm 3 measuring cylinder,
100 cm 3 beaker,
100 cm3 conical flask,
50.0 cm 3 burette,
10.0 cm3pipette,
glass rod,
white tile,
pipette filler,
weighing bottle,
thermometer.
Hazard Warning
Butanedioic acid is irritant. Diethyl ether is flammable. Phenolphthalein indicator is flammable and
harmful. Wear safety goggles during the experiment.
Principle:
If a solute is soluble in two different solvents, it usually has different solubilities in each of them. If
the two solvents are immiscible and the solute is added to them, it will distribute itself between the two
solvents according to its respective solubilities. An equilibrium is then set u p between the
solute particles in one solvent and the solute particles in another solvent. The ratio of
the concentrations of the solute in the two solvents is called partition coefficient or distribution
coefficIent.
In this experiment, the partition coefficient of butanedioic acid between water and diethyl
ether is determined.
P.1
Experiment P13
To determine the partition coefficient of butanedioic acid (HO 2C(CH2)2CO2H)
between water and diethyl ether (CH 3CH2OCH2CH 3)
Procedures:
A.
Setting up of Equilibrium
1.
Measure 40.0 cm 3 of distilled water or deionized water using a 50 cm 3 measuring
cylinder. Pour it into a 100 cm3 beaker.
2.
Weigh about 2.0 g of butanedioic acid and record the mass weighed.
3.
Pour the weighed butanedioic acid into the beaker containing 40.0 cm3 of distilled
water.
4.
Stir the mixture using a clean and dry glass rod until all butanedioic acid dissolves.
5.
Pour the mixture into a clean and dry 100 cm 3 separating funnel.
6.
Measure 40.0 cm3 of diethyl ether using a 50 cm3 measuring cylinder. Pour it into the
separating funnel.
7.
Stopper the funnel and shake vigorously for 2 minutes. Open the tap occasionally to
release the pressure in the funnel. (Caution: Diethyl ether is very volatile and
flammable. Make sure that there is no flame nearby and do not point the tip of the
funnel towards anyone.)
8.
Place the separating funnel in the ring. Leave it to stand for several minutes until its
contents separate into 2 clear and steady layers.
9.
Measure and record the room temperature using a thermometer.
P.2
Experiment P13
To determine the partition coefficient of butanedioic acid (HO 2C(CH2)2CO2H)
between water and diethyl ether (CH 3CH2OCH2CH 3)
B.
Titration of the aqueous layer
1.
Pour 0.50 M sodium hydroxide solution into the burette through a filter funnel.
2.
Open the cork of the separating funnel and then the stopcock. Run off the
aqueous layer (lower layer) from the tip into a clean and dry 100 cm 3 beaker.
Discard the fraction just below and above the boundary of the two layers into
another beaker.
3.
Pipette 10 cm3 of the aqueous layer into a 100 cm3 conical flask.
4.
Add 2 drops of phenolphthalein indicator into the conical flask.
5.
Record the initial burette reading in Table 1.
6.
Titrate the aqueous solution in the conical flask with 0.50 M sodium hydroxide
solution in the burette.
C.
7.
Record the final burette reading in Table 1.
8.
Repeat steps 3-7 to obtain 2 sets of consistent results.
Titration of the Ethereal Layer
1.
Pour 0.10 M sodium hydroxide solution into the burette through a filter funnel.
2.
Run off the remaining layer (ethereal layer) in the separating funnel into a clean
and 100 cm3 dry beaker.
3.
Pipette 10 cm3 of the ethereal layer into a 100 cm3 conical flask.
4.
Add about 10 cm3 of distilled water or deionized water into the conical flask.
5.
Add 2 drops of phenolphthalein indicator into the conical flask.
6.
Record the initial burette reading in Table 2.
7.
Titrate the aqueous solution with 0.10 M sodium hydroxide solution.
8.
Record the final burette reading in Table 2.
9.
Repeat steps 3-8 to obtain 2 sets of consistent results.
P.3
Experiment P13
To determine the partition coefficient of butanedioic acid (HO 2C(CH2)2CO2H)
between water and diethyl ether (CH 3CH2OCH2CH 3).
Results
Mass of weighing bottle and butanedioic acid:
Mass of weighing bottle:
Mass of anhydrous butanedioic acid used:
Room temperature =
°C
Table 1
Titration
1 (trial)
2
3
2
3
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Average of sodium hydroxide used =
Table 2
Titration
1 (trial)
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of NaOH used (cm3)
Average of sodium hydroxide used =
P.4
Experiment P13
To determine the partition coefficient of butanedioic acid (HO 2C(CH2)2CO2H)
between water and diethyl ether (CH 3CH2OCH2CH 3)
Name:
Seat No.:
Date:
Questions
1.
Calculate the concentration of butanedioic acid in the diethyl layer in mol dm-3.
2.
Calculate the concentration of butanedioic acid in the aqueous layer in mol dm-3.
3.
Determine the partition coefficient of butanedioic acid between diethyl ether and water.
P.5