(Prelim) Expt 2 Prelab MP Determination

Question 1

Any property of a substance that can be observed without transforming the
substance into some other substance

Answer 1

Physical Property

Question 2

1. Research on the theoretical melting point of ALL samples to be used as a guide in actual determination of the melting point.
2. Using a Bunsen burner, prepare 5 capillary tubes by sealing one end.
3. Pulverize each separately using a mortar and pestle and form a heap of each sample.
4. Introduce each sample gradually into the capillary tube occupying 1 cm of the capillary tube.
5. Heat the melting point apparatus to a temperature 30°C below the lowest point of the theoretical melting point of all the samples.
6. Raise the temperature of the apparatus slowly at a rate of 1-2 °C per minute.
7. Introduce the capillary tube with the sample in the apparatus when the temperature is 5-6 °C below the theoretical melting point.
8. Record the temperature range at which samples begins to liquefy until it has completely liquified. Note any sintering, coloring, softening or any signs of
   decomposition.

Answer 2

Accurate Method

Question 3

the common Physical Properties that are being measured:

Answer 3

• Melting Point
• Boiling Point
• Solubility

Question 3

Dependent on the intermolecular forces of attraction between the solid particles and the packing of the crystal structure

Answer 3

Melting Point

Question 3

1. Research on the theoretical melting point of naphthalene and benzoic acid to be used as a guide in actual determination of the melting point.
2. Using a Bunsen burner, prepare 3 capillary tubes by sealing one end.
3. Pulverize each naphthalene and benzoic acid separately using a mortar and pestle and form a heap of each sample.
4. Introduce each sample gradually into the capillary tube occupying 1 cm of the capillary tube.
5. On the 3rd capillary tube, add a mixture of naphthalene and benzoic acid in a 1:1 ratio
   occupying 2 cm of the capillary tube.
6. Attach the capillary tubes with the samples to the thermometer using a ring of rubber
   tubing. The capillary tube should be attached in a manner that the solid sample inside
   the capillary tube is alongside the bulb of the thermometer.
7. Immerse the thermometer with the capillary tube in the mineral oil bath and heat the
   bath.
8. Record the temperature range at which the pure substance and the mixture begins to
   liquefy until it has completely liquified. Note any sintering, coloring, softening or any
   signs of decomposition.

Answer 3

Rough Method

Question 4

Temperature at which a given solid material changes from a solid state to a
liquid, or melts.

Answer 4

Melting Point

Question 5

Melting points are determined for three reasons:

Answer 5

1. If a compound is a known one, the melting point will help to characterize the sample.
2. If the compound is new, then the melting point is recorded to allow future characterization by others.
3. The range of the melting point is indicative of purity of the compound – an impure compound will melt over a wide range of temperatures

Question 6

Rough Melting Point Method Sample

Answer 6

Naphthalene
Benzoic Acid

Question 7

Accurate Melting Point Method

Answer 7

*Benzoic Acid
*Sodium Benzoate
*Urea
*Salicylic Acid
*Napthalene