2. Partition coefficient of succinic acid
Theory:
see Partition coefficient coefficient of succinic succinic acid, acid, p. 2-12 in Kopecký F., Kaclík P., Fazekaš T.: Laboratory manual for physical chemistry, Department of Physical Chemistry, FaF UK
Task: Determine the partition coefficient of succinic acid in system of two immiscible liquids: 1-butanol – water. With the aim to increase the accuracy of result, the measurement will be performed at 4 different concentrations of succinic acid and different volume ratios of partitioned mixture (1-butanol – water). Equipment and chemicals: 4 separation funnels (100 ml), 4 titrimetric flasks, fl asks, 2 burettes, pipettes, 8 beakers 3 3 succinic acid (aqueous solution c=20mg/dm ), NaOH (c=0.05 mol/dm ), 1-butanol, phenolphthalein, distilled water Procedure:
1. 2. 3.
4. 5. 6. 7. 8. 9. 10.
Prepare 4 mixtures of butanol, water and succinic acid into separation funnels following the Tab. 2.1. Shake gently the separating funnels with prepared solutions for 20 min. Put them to the holders and wait a few minutes until the mixture is apparently separated into two clear layers: lower layer is water (Wat), and upper layer is butanol (Org). Pour carefully the water phase into a beaker using the funnel’s valve. Transfer the water solution from the beaker into two titrimetric flasks, 5 ml per flask, using pipette (V=5 ml). Add 2-3 drops of phenolphthalein. Fill a burette with a standard solution of NaOH (titrant) and perform titration. When the endpoint of titration has been reached, read the used volume of NaOH from the burette ( V T T). Write it down to the table Tab. 2.2. Repeat the procedure for funnels 2 – 4. Proceed in the same way the upper layer (butanol) of the mixtures in the funnels No. 1-4.
Data treatment: 1. Calculate the average volume of titrant ( V T ) from 2 titrations of the same solution in the Tab. 2.2. 2. Succinic acid is a diprotic acid. Process Process of titration is based on the neutralization reaction:
CH2-COOH I
CH2-COOH
+ 2 NaOH
CH2-COONa →
I
CH2-COONa
+ 2 H2O
3. Calculate the concentration of succinic acid in the water and organic phase, cWat, cOrg, respectively, for each composition of the partition mixture (according to manual for titration). Remember, an analyte is the succinic acid, the volume of V A=5 ml. 4. Calculate the partition coefficient k of succinic acid at each composition of the partition mixture. cOrg k = cWat 5. Express the average value of the partition coefficient k from four experiments.
Tab. 2.1. Composition of partition mixtures. Funnel No. 1 2 3 4
Succinic acid (ml) 20 10 15 10
Water (ml) 15 10
1-butanol (ml) 15 15 15 15
Tab. 2.2. Experimental data. No. I.
Volume of titrant VT (ml) 1-butanol water II. Mean I. II.
The report must include: •
Theory (partition coefficient)
•
Equipment and chemicals
•
Working procedure and measurements
•
Tables of results and calculation
Mean
cOrg (M)
cWat (M)
k
•
In conclusions, give the obtained average value of partition coefficient from 4
experiments.
Used literature: Kopecký F., Kaclík P., Fazekaš T.: Laboratory manual for physical chemistry, Farmaceutical faculty of Comenius University, Bratislava,1996 J. Oremusová, Manual for laboratory practice in physical chemistry for students of pharmacy, Department of Physical Chemistry, Faculty of Pharmacy, Comenius University, Bratislava, 2007, in Slovak Manual written by Doc. RNDr. D. Uhríková, CSc.