Cloud in a Bottle
This experimentillustrates the effect of pressure change and aerosols on cloud formation.
1) Two clear, empty, plastic water bottles withlids. Remove labels.
· Forthe first bottle, add about 1 inch of hot tap water and put the lidon. Shake vigorously.
· Lookthrough the bottle. It is best viewed ingood lighting against a dark background.
· Squeezethe bottle as hard as you can, then release it. Repeat this 5 or 6 times.
· Youare trying to see if there is any change in the air inside the bottle. To get a clear view, swirl the water aroundto remove condensation from the inside walls of the bottle.
· Forthe second bottle, again add about 1 inch of hot tap water, put the lid on, andshake.
· Takethe lid off, light a match, blow it out, drop it into the bottle while it isstill smoking, then immediately put the lid back on the bottle.
· Againlook through the bottle, squeeze the bottle as hard as you can, then releaseit. Repeat this several times. Swirl the water as needed to removecondensation from the inside walls of the bottle.
· Safetyprecautions are always important “in the lab”. Take a moment to put the matches away, out ofreach of children. Thanks!
Which bottle had better cloudformation, the one with smoke in it, or the one without?
Did the cloud appear when you caused high pressure on the air in the bottle (bysqueezing), or when you caused low pressure (by releasing)?
What is happening?
The warm moist air in thebottle is close to saturation. Squeezingthe bottle increases the air pressure which also causes an adiabatictemperature increase. This increasedtemperature allows more water to evaporate. Releasing the bottle decreases the pressure and temperature slightly andcauses the excess water vapor to condense. The smoke particles are condensation nuclei which improve cloudformation.
The formation of the cloudwhen the pressure decreases is analagous to what happens to a parcel of airrising in the atmosphere.
Answer the following questions,based on the experiment and these sections in your textbook: Dew-Point Temperature, page 495
Adiabatic Temperature Changes, page 498
Condensation and Cloud Formation, page 596
The amount of vapor needed forsaturation ________ with increasing temperature.
Saturation occurs if sufficient watervapor is added to air, or if air is cooled to its dew point.
Cooling below the ________ causeswater vapor to condense.
Air that is allowed to expand________; air that is compressed________.
When a parcel of air moves upward,it expands and cools.
In order for a cloud to form, airmust be cooled below its _____ point.
In the experiment, squeezing thebottle causes pressure and temperature to ________; releasing the bottle causespressure and temperature to _________.
Tiny bits of particulate matterknown as ________ serve as surfaces for water vapor condensation.
Give two examples of condensation nuclei.
Explain why the cloud appeared whenyou released the bottle.