This document describes an experiment to determine the partition coefficient of benzoic acid between benzene and distilled water. The experiment involves preparing mixtures of benzoic acid saturated benzene solution and water in separating funnels, allowing the benzoic acid to distribute between the solvents, then measuring the concentrations in each solvent layer by titration. The partition coefficient is the ratio of concentrations of solute in the two solvents at equilibrium and this experiment aims to calculate it for benzoic acid between benzene and water.

1. Experiment 10
To determine partition
coefficient of benzoic acid
between benzene and distilled
water.
SRP: Partition Coefficient
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2. SRP: Partition Coefficient
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 When a solute is shaken with two immiscible solvents it gets distributed between the
solvents.
 This distribution of solute in two solvents depends upon the solubility of the solute in two
solvents.
 At the distribution equilibrium, the ratio of concentration of the solute in the two solvents is
constant at a given temperature.
 The constant is called the partition coefficient (K) or the distribution coefficient of the solute
between the two solvents
To determine the partition co-efficient of benzoic acid between benzene and water.

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REQUIREMENTS:
Chemicals: Saturated solution of benzoic acid in benzene Benzene
• 0.01N NaOH
• 0.1N NaOH
• Distilled water
Apparatus: Separating funnel: 250 ml, Conical flask, Pipette, Burette and Stoppered bottles
Separating funnel Conical flask Pipette
Burette
Stoppered bottles

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PROCEDURE: Prepare the following mixtures in separating funnels:
Set I: 25ml water + 25 ml of saturated solution of benzoic acid in benzene
Set II: 25 ml water + 20 ml saturated solution of benzoic acid in benzene + 5 ml benzene
Set III: 25ml water + 15 ml saturated solution of benzoic acid in benzene + 10 ml benzene
Shake the mixture in the separating funnel vigorously for about 30 minutes so that the benzoic acid gets distributed between
the two solvents and the distribution equilibrium is reached. Allow the flasks to stand for 10 minutes to separate into two
clear layers (remove the stopper of the separating funnel and keep its mouth open during this period to facilitate the
separation). Drain off the lower aqueous layers in 3 different stoppered dry bottles. (Discard the intermediate layer between
the two phases). Benzene layer remains in the separating funnels. Using a dry pipette take 5 ml of organic layer (Benzene)
into a conical flask containing 10ml of water and titrate against 0.1 N NaOH using TCI FEP Fluoropolymer Films FEP Films
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not to show that ad again Ad closed by phenolphthalein as an indicator. End point: Colorless to pink.Pipette out 10 ml of the
aqueous layer using a dry pipette and titrate it against 0.01 N NaOHsolution using phenolphthalein as an indicator. End point
will be colorless to pink.

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Similarly calculate concentration of benzoic acid in aqueous layer of sets II and III.
Similarly calculate concentration of benzoic acid in aqueous layer of sets II and III.

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Reference: More HN, Hajare AA. Practical Physical Pharmacy, Career publications, 2010: 73-76.