Page 21 - Chemistry - XI

EXPERIMENT - 9

Objective

Determination of boiling point of a liquid organic compound.

Principle/Theory
The boiling point of a liquid is the temperature at which vapour pressure of the liquid becomes equal to the
atmospheric pressure. Diff erent liquids have diff erent boiling points because they have diff erence in the
intermolecular forces operating between the molecules of the liquid.

Materials Required
Beaker (250 mL) or Thiele’s tube, ignition tube (fusion tube), thermometer 110°C, rubber band, laboratory
stand with clamp and ring, burner, tripod stand and wire gauze, and liquid organic compound (benzene/
acetone/acetic acid)

Procedure

1. Take 1–2 mL of the given liquid in an ignition tube
and tie it with the bulb of the thermometer with a
rubber band. Capillary tube
2. Place it in a beaker half fi lled with water (Fig. 9.1). Fusion Tube
3. Seal one end of the capillary tube by heating the tip
on a bunsen burner or spirit lamp.

4. Place this capillary tube with its open end downward
in the ignition tube.
5. Heat the beaker with a bunsen burner and stir the
water gently.

6. Observe the escape of bubbles at the lower end of the
capillary tube. Fig. 9.1
7. Note down the temperature at which brisk evolution of bubbles occurs at the lower end of the capillary
tube. This temperature is the boiling point of the liquid.

Result

1. The boiling point of the given liquid is ___________ °C.

VIVA VOCE

Q1. Defi ne boiling point.
Ans. The temperature at which the vapour pressure of the liquid becomes equal to the atmospheric
pressure (external pressure) is the boiling point of the liquid.

Q2. Explain in brief why does a liquid boil.
Ans. When we heat a liquid, the kinetic energy of molecules increases and its vapour pressure increases.
When we heat a liquid, the kinetic energy of molecules increases and its vapour pressure increases.
When the vapour pressure of liquid becomes equal to the atmospheric pressure, the liquid starts
When the vapour pressure of liquid becomes equal to the atmospheric pressure, the liquid starts
boiling.
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