Recrystallization (Page 2 of 4) in pdf

Part 2. Solubility Tests

In the second part of today's experiment, you will test the solubility properties of

resorcinol and benzoic acid (see structures below) in seven different solvents: methanol,

ethanol, acetone, acetic acid, water, toluene and ligroin (also known as petroleum ether).

See LTOC, Section 15.4, and the table on page 222. Knowing the solubility properties,

you will be able to draw some conclusions regarding an appropriate recrystallization

solvent or solvents for each compound.

Resorcinol

Benzoic acid

Use a flow chart format to outline the steps of the following procedure (see below

for an example). You should perform these tests while your phthalic acid is crystallizing.

Mix 20-30 mg of solid

with methanol. Stir!

soluble?

yes

Add a few drops of water

Heat mixture in water bath

precipitate?

yes

etc.

Caution! Methanol, ethanol, acetone, toluene and ligroin are flammable!

To test the solubility of a solid, transfer a “spatula-tip” full of the compound (you

may weigh out 20-30 mg of one of the solids to get an idea of how much should be used)

into a 10x75 mm test tube and add 10 drops of solvent. Stir with a thin stirring rod, break

up any lumps, observe and record whether or not the solid is readily soluble at room

temperature.

If the solid does not dissolve in a given solvent at room temperature, heat the test

tube containing the mixture in a beaker of water heated on a hot plate. If the solid

Recrystallization Page 2