Working on a demonstration to show that water in a flask can

Working on a demonstration to show that water in a flask can oil at a room temperature of 30 C

Solution

Water at room temperature in a flask boils vigorously.

MATERIALS

PROCEDURE:

With the use of a mechanical vacuum pump, water in a flask can be made to boil so vigorously at room temperature . Apparatus for such a cryophorus demonstration can be purchased or constructed.If constructed, one should use a thick, round-bottom boiling flask and a trap which can be filled with strong sulfuric acid to isolate the flask from the vacuum pump. The acid absorbs the water vapor thereby increasing the rate of boiling as well as preventing the pump oil from being contaminated with water. The use of distilled water is recommended. The water can be brought to a boil more quickly if it is preheated. A large pressure gauge visible to the audience is a useful addition.

This demonstration is best introduced by asking the audience at what temperature water will boil. Most people will answer with 212°F or 100°C. One should point out that this answer is correct only at atmospheric pressure (760 torr), and that it is well-known by the residents of high-altitude cities that it takes longer to cook a boiled egg there because water boils at a lower temperature at higher altitude. It\'s not accurate to say that it takes longer to boil an egg there because the water is actually brought to a boil more quickly. The barometric pressure drops by about 3% for each 1000 feet above sea level. A city such as Denver, Colorado is at an altitude of about 5000 feet, and thus the average barometric pressure is around 660 torr, and the boiling point of water is about 96°C. On top of Mt. Everest (29,028 feet) it\'s a chore to make a pot of tea. One can point out that a boiling liquid tends to maintain a constant temperature, and this is why many foods are cooked in boiling water. In a pressure cooker, the boiling point is raised by the increased pressure.

One then turns on the vacuum pump and lets the audience watch while the water boils furiously.

DISCUSSION

The heat of vaporization of water is 540 calories per gram, and the heat of fusion of water is 80 calories per gram. The density of water is 1 gram per milliliter. When the water evaporates, a large amount of heat is thus extracted from the water, causing the cooling