ENTHALPY OF VAPORIZATION OF WATER



ENTHALPY OF VAPORIZATION OF WATER

The purpose of this lab is to determine the vapor pressure of water at various temperatures, and from these data to calculate ∆Hvaporization for water.

Procedure

Bring two 600 mL beakers of water to a boil on your hot plate. Fill a tall 1000 mL beaker nearly full with hot tap water. Fill a small graduated cylinder about 1/2 with tap water, seal it with thumb or finger, and invert it into the beaker of water. The volume of trapped air should be around 5 mL (if it isn’t, try again). Use clamps or string to support the inverted cylinder in a vertical position, not touching the beaker. Suspend a thermometer near the cylinder.

Add boiling water to the large beaker to bring the water to about 75 °C. Make sure the inverted cylinder is completely submerged. Put the beaker on the stir plate and stir gently as you read and record the temperature and trapped air volume (bottom of the meniscus) about every 5 °C until the water has cooled to about 50 °C.

Now you need to add cold water and eventually ice to bring the temperature down to less than 5 °C, without disturbing the trapped air and preferably without flooding the lab. You can move the beaker (without stirrer!) into the sink and run cold water in it; you can set up a siphon and siphon out warm water as you add cold water: devise your own clever method for replacing the warm water with cold water without messing up the trapped air. Bottom line: get the temperature down below 5 °C, and take your final reading of temperature and trapped air volume. Read and record barometric pressure.

Analysis and Discussion

If we assume that the vapor pressure of water is negligible at ................
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