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  • Read the passage carefully and answer the following questions: a) Why do we dissolve oleic acid in alcohol? b) What is the role of lycopodium powder? c) What would be the volume of oleic acid in each mL of solution prepared?

In an experiment to estimate the size of a molecule of oleic acid, 1mL of oleic acid is dissolved in 19mL of alcohol. Then 1mL of this solution is diluted to 20mL by adding alcohol. Now, 1 drop of this diluted solution is placed on water in a shallow trough. The solution spreads over the surface of water forming one molecule thick layer. Now, lycopodium powder is sprinkled evenly over the film we can calculate the thickness of the film which will give us the size of oleic acid molecule.

Read the passage carefully and answer the following questions:

a) Why do we dissolve oleic acid in alcohol?

b) What is the role of lycopodium powder?

c) What would be the volume of oleic acid in each mL of solution prepared?

d) How will you calculate the volume of n drops of this solution of oleic.

e) What will be the volume of oleic acid in one drop of this solution?

Answers (1)

(a) We can reduce the concentration of oleic acid by dissolving it in a proper solvent to get a molecular level. It can be dissolved in organic solvent alcohol and not ionic solvent water since it is an organic compound.

(b) Mixing of oleic acid in water is prevented by Lycopodium when a drop of oleic acid is poured on water. Thus, if we spread lycopodium powder on the water surface, the layer of oleic acid will be formed on the surface of the powder,

(c)(\frac{1}{20})(\frac{1}{20\; V}) = \frac{V}{400} ml is the concentration of oleic acid in an alcohol solution. Its required conc. in 1 ml solution is 1/400 ml.

(d) By dropping one ml of solution drop by drop in a beaker through burette and counting its no., can be used to calculate the volume of n drop solution. If there is 1ml of n drop, then its volume will be 1/n ml.

(e)  If there is 1ml of n drop, then its volume will be 1/n ml. The concentration of oleic acid in one drop of the solution will be

\frac{1}{400\; V}=\frac{1}{400}.\frac{1}{n}ml

=\frac{1}{400}ml of oleic acid.

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