Experiments for the determination of the melting point

Summary

This experiment is from the official website of Tianjin Agricultural College

Operation method

Experiments for the determination of the melting point

Principle

Pure crystalline organic compounds have a certain melting point, the melting range does not exceed 0.5 ℃, when there are impurities when the melting point drops, the melting range is widened. The use of the determination of melting point can determine the purity of solid organic compounds, identify different organic compounds. Melting point: at atmospheric pressure, the compound is heated by the solid state into a liquid state, the solid-liquid two-phase vapor pressure is consistent, solid-liquid two-phase equilibrium coexistence, the temperature at this point is called the melting point of the compound.

Materials and Instruments

Acetanilide Benzoic acid; 8-hydroxyquinoline Glycerine Ethanol 95 %
Thiele tubes Thermometers Melting point tubes Long glass tubes Surface dishes Files Incisions Cork Gum plugs Rubber rings Microscopic melting point tester Tweezers

Move

[Instruments, medicines]

Instruments: ① Thiele tube; ② 100 ℃, 200 ℃ thermometer; ③ melting point tube, long glass tube (60 cm);

④ surface dish (medium size), file, cut cork, glue plug, rubber ring

⑤ Micro melting point tester, tweezers, etc.

Drugs: unknown 1: acetanilide; unknown 2: benzoic acid; unknown 3: 8-hydroxyquinoline

Glycerol (hot carrier); ethanol 95 %

1. The sample should be finely ground and packed so that the heat is conducted quickly and evenly.

2. Control the rate of temperature rise, slightly faster at the beginning, and gradually slower when approaching the melting point.

3. Each sample measured three times (coarse measurement once, fine measurement twice).

4. Observe the temperature of the thermometer.

5. Replace the other tube when the temperature of the oil bath falls below 30 °C.

6. Install correctly and operate rigorously.

7. With the melting point tester to measure the melting point, take and put the coverslip and heat insulation glass, must use tweezers to hold, is strictly prohibited to touch the hand, so as to avoid scalding (because of the melting point of the hot plate belongs to the high-temperature components).

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