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Vapor Pressure of Gas/Liquid

Last updated

Aug 15, 2020
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- Vanishing Water
- Vinegar Cannon

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In this demonstration the reddish brown color of the Br₂ vapor in a sealed vessel intensifies as the vessel is heated

Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves

Equipment	Chemicals
Seal tubes w/ Br	Water
Hot Plate	Ice bath (ice, water and NaCl)
Two 500ml beakers or two 1000ml beakers

Procedure:

Prepare a warm water bath by heating 300ml water to 50^oC in 500ml beaker. Do not place tubes in water bath if temp is greater than 58^oC.
Prepare ice-water bath 250ml ice in 500ml beaker and add 50ml water.
Place a bromine tube in the ice water bath and the bromine vapors will condense.
Place a bromine tube in the warm water bath and the bromine vapors will expand and be most intense.

Discussion:

Bromine is a reddish brown, volatile, diatomic liquid with a suffocating odor. Its melting point is -7.25^oC and its normal boiling point is 59.47^oC. Bromine is suitable for demonstrating the effects of temperature on the vapor pressure of a liquid. The intensity of a deep reddish brown color of the vapor is a direct indication of the vapor pressure.

Hazards:

The boiling point of bromine is 59^oC, and the vapor pressure of bromine is over 1 atm above this temperature. Therefore the tubes should not be immersed in baths above this temperature, to avoid creating high pressures within the tubes.

SOP:

Corrosive – Barium Hydroxide, Sulfuric Acid

Disposal (by Storeroom)

Slowly pour a concentrated sodium thiosulfate (Na₂S₂O₃) solution into the cylinder until the bromine has been reduced. Caution! Exothermic reaction, the mixture will become hot. Flush the resulting cooled solution down the drain with water.

Acknoledgement and adapted from:

B. Z. Shakhashiri Chemical Demonstrations; A Handbook for Teachers of Chemistry Vol.2, Wisconsin, 1989, Vol.2, p.75-77

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