Download Name: David Kett Id Number: 0564591

Title: Like Dissolves Like: Solubility of Organic Compounds
Aim: To observe the solubility of organic compounds and the hydrocarbon Hexane in
both water and acetone and to examine the effects of increased carbon-chain on
solubility.
Target Group: Suitable for a Senior cycle Chemistry class with sufficient prior
knowledge and understanding of the concepts dealt with.
Solubility Background
If the intermolecular forces between the molecules of one substance are roughly the
same as the intermolecular forces between the molecules of another substance, then
the two substances will most likely dissolve in each other. Thus, polar substances
such as water can dissolve other polar substances such as alcohols and carboxylic
acids. Water can be broken down into H - OH, thus it has the -OH group which
identifies alcohol and carboxylic acids. Non polar substances, however, such as
hydrocarbons (E.g. Hexane) dissolve in other non polar substances, but do not tend to
dissolve in polar substances
The hydrocarbon portion is said to be hydrophobic (water hating) because it
will not hydrogen bond with water but does tend to dissolve in hydrocarbon liquids.
The water-like alcohol and carboxylic acid groups hydrogen bond with water and are
said to be hydrophilic (water-loving). Thus, the solubility of alcohols, aldehydes and
carboxylic acids in water is made smaller when the hydrophobic portion of the
molecule is made larger.
Safety Hazard:
Alcohols are flammable liquids and so students must exercise caution when handling
them. Appropriate eye protection must be worn and students are instructed not to
leave any unknown material in the waste disposal.
Chemicals Required:
Organic Compounds: Methanol; Butan-1-ol; Ethanal; Butanal; Methanoic Acid;
Butanoic Acid; Hexane;
Solvents: Water; Acetone; 0.01% w/v Methlyene blue solution.
Apparatus Required:
14 Test – tubes; 7 small beakers; 7 droppers.
Experimental Method:
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Organic Compounds (Alcohols, Carboxylic Acids, Aldehydes and Hexane) are
tinted with 0.01% w/v Methylene Blue; to allow for ease in examination of
solubility of the compound.
20 ml of each compound is placed in a small beaker and labelled
appropriately.
Ten drops of water and an equal amount of acetone; are placed in respective
test tubes.
The organic compound (Methanal, Butan-1-ol etc.) is added drop wise to the
solvent in the test tube, stirring until a total of five drops have been added.
Repeat procedure for remaining chemicals.
Record solubility or lack of, in table below.
Sample results/Observations:
Organic Compound
Water
Acetone
Ethanol
(ethyl alcohol)
Soluble (10 drops)
Soluble (10 drops)
Propan-1-ol
Soluble (17 drops)
Soluble (20 drops)
Sucrose
(table sugar)
Insoluble
Insoluble
Insoluble (20 drops)
Soluble (30 drops)
Soluble(9 drops)
Soluble (5 drops)
Insoluble (Less Dense)
Insoluble (More Dense)
Butanal
Methanoic Acid
(formic acid)
Olive Oil
State whether soluble or insoluble in the rows provided, or in certain cases, the
number of drops resulting in solubility or insolubility.
Conclusions:
The pupils discover that the longer the carbon chain in the alcohol, the less soluble it
is in water. Branching however, in the case of Propan-1-ol, increases solubility as a
result in the reduction in the size of the hydrophobic portion with respect to the
hydrophilic one. All of the alcohols are soluble in acetone, thus acetone is a good
solvent for a wide variety of substances.
Possible Questions:
1. Pupils can be asked to orally define the rules of solubility of organic
compounds in water and acetone.
2. To explain the meaning of the ‘like dissolves like’ principle
3. What trend can be found in the solubility of alcohols in water when the
number of carbons is increased?
Links to Irish Curriculum:
Solubility has high relevance with regard to the Irish curriculum especially with
regard to organic compounds as wholes sections are devoted to this area. It is also
important to have a good understanding of the concepts of polar and non polar when
considering solubility and the solvents available.