Remarks
Volatility of liquids is dependent upon the strength of the intermolecular forces. Discussion of London dispersion forces, dipole-dipole interaction, and hydrogen bonding should be utilized. The effect of structural isomerism on the degree of polarity is nicely illustrated.
Figure 11. Boiling points, vapor pressures, and heats of vaporization for selected liquids.
Reference
This demonstration is modified from Experiments and Demonstrations for the 1986 ICE Workshop in Tucson.
Demonstration 2: Boiling Water the Fast Way
Description
Warm water is drawn into a large syringe, and the end is sealed. When the plunger of the syringe is drawn out and the pressure drops, the warm water quickly boils.
Materials
Plastic syringe, 30-mL or 50-mL Cap for the syringe Beaker of warm water
Hazards
If the water is too warm, a skin burn may result.
Procedure
1. Place open end of syringe into the beaker of warm water. The water does not have to be extremely warm; 50°C to 60°C suffices. In fact, the lower the temperature at which the water can be made to boil, the more impressed students will be.
2. Draw approximately 10-mL water into the syringe.
3. Place the plastic cap on the end of the syringe if one is available. If no cap is available to seal the syringe, place the end of your index finger over the end of the syringe or plug the end with modeling clay. 4. Pull on the plunger until it is nearly out of the syringe. Do not pull so hard as to ÒpopÓ the plunger completely out of the syringe. The water should begin to boil. If it does not, try warmer water.
5. Let the plunger slide back into the syringe. The boiling will stop. Repeat this process as often as you like. You will need to use a fresh sample of warm water once boiling cannot be sustained. It is possible to get the plunger to stay out by drilling a hole in the stem of the plunger and inserting a nail in the hole as the plunger is extended. This will help to keep your fingers from getting tired.
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