APPARATUS: Melting point apparatus, 250 tal beaker containing high boiling point oil (Liquid paraffin or glycerol) 210° C thermoraéter, three semi-micro test-tubes with corks, two semi-micro
egetaljinde
, benzoic acid, hydroquinone, biphenylee
stirring rods
, some melting point társes, camphor, naphthalene, organic substance whose molecular
weight is to be determined (e. g.
PROCEDURE:
Place some camphor in a semi-micro test tube; in a second semi-micro test tube weigh accurately
about 0.10 g naphthalene and add about 1.0 g camphor and re-weigh. In a third semi-micro test-tube
weigh accurately about 'e-10 g of substance whose molecular weight is be determined followed by
about 1.0 g camphor and re-weigh. Label the three test tubes, cork loosely and heat in the oil bath
until just completelyzínelted.
Stir the two solutions thoroughly, using semi-micro stirring rods. Then take two samples from each
test-tube by kúpping melting point tubes into each solution and seal the tubes above the sample. By
means of the melting point appartus, determine to 0.1° the melting point of each sample, which is
when the last crystal disappears.
Questions on Experiment
1. Calculate Kc for camphor.
2. Calculate the molecular weight of the given substance..
3. Why is camphor often made the solvent in the determination of molar mass by freezing point
depression method?
4. What is meant by colligative properties? List the colligative properties of a solute-solvent system?
5. Why is the freezing point depression method of determining molar masses often chosen?
6. Which of the colligative properties would you measure when dtermining the molar mass of
proteins? Give reasons.
7. List the relevant equations used for the determination of molar mass from colligative properties.​