Experiment 7
Experiment 7 The partition of Organic acid between Water
and Organic solvent
Objectives
Understand the partition of a solute between two immiscible solvents.
Introduction
A chemical analysis that is performed primarily with the aid of volumetric glassware (e.g.,
pipets, burets, volumetric flasks) is called a volumetric analysis. For a volumetric analysis
procedure, a known quantity or a carefully measured amount of one substance reacts with a
to-be-determined amount of another substance with the reaction occurring in aqueous
solution. The volumes of all solutions are carefully measured with volumetric glassware.
The known amount of the substance for an analysis is generally measured and available in
two ways:
1. As a primary standard: An accurate mass (and thus, moles) of a solid substance is
measured on a balance, dissolved in water, and then reacted with the substance being
analyzed.
2. As a standard solution: A measured number of moles of substance is present in a
measured volume of solution - a solution of known concentration, generally expressed as
the molar concentration (or molarity) of the substance. A measured volume of the
standard solution then reacts with the substance being analyzed.
The reaction of the known substance with the substance to be analyzed, occurring in
aqueous solution, is generally conducted by a titration procedure.
The titration procedure required a buret to dispense a liquid, called the titrant, into a flask
containing the analyte. A reaction is complete when stoichiometric amounts of the reacting
substances are combined. In a titration this is the stoichiometric point. In this experiment the
stoichiometric point for the acid-base titration is detected using a phenolphthalein indicator.
Phenolphthalein is colorless in an acidic solution but pink in a basic solution. The point in the
titration at which the phenolphthalein changes color is called the endpoint of the indicator.
Indicators are selected so that the stoichiometric point in the titration coincides (at
approximately the same pH) with the endpoint of the indicator.
