Introduction to Gases
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Barbara Pawela Retired
1. To demonstrate that gases are a state of matter.
2. To generate a number of gases.
3. To discover some properties of gases.
4. To compare some of the properties of different gases.
5. To relate the Kinetic Molecular Theory to the change of state
Activity 1 Activity 2 Activity 3 Activity 4
balloons balloons dry yeast 1/2 t. powdered sulfur
plastic bags vinegar hydrogen peroxide 1/2 t. iron filings
clay baking soda large test tube crucible
transparent small bottles balloon hot plate
pan or bowl egg shells wooden splint
candle wooden splint matches
Activity 5 (optional) Activity 6
a few iodine crystals shoe box
sealed flask small light-weight spheres
5 mL hydrochloric acid
a few zinc chips
large test tube
Set up stations for the different activities and have the materials needed
for each activity ready. Group the students into teams of four. Remind the
students about science lab safety rules.
Begin the presentation by asking the students what they see in front of their
nose. Let students respond. Tell the students to wave their hand in front
of their face. Discuss and conclude that although they could not see the air
in front of their face, they could feel it as a breeze against their skin.
Spray a little room deodorant or perfume. Ask the students to raise their
hand when they smell something. The smell will diffuse and, depending on the
distance away from the source, the students will raise their hands at
Have some of the students blow air into balloons, and some students blow air
into plastic bags. Discuss and conclude that air takes up space.
Wave a sound tube or use something to make a sound. Discuss and conclude
that the sound vibrations are being transmitted through the air.
These three demonstrations help to show that: although the air cannot be
seen, it can be felt; an odor can be diffused through it; and sound
vibrations can be transmitted through it, air is matter and does exist and
take up space. Discuss and conclude that air is a mixture of gases.
Stick clay pieces on the base of a candle and on the opposite sides of the
rim of a tall glass. Stand the candle in a transparent container. Pour water
into the container so that about one-third of the candle is in the water.
Light the candle for a few seconds, then place the open end of the glass over
the candle. Observe what happens. In a short while the flame goes out. The
water level in the glass will rise. Discuss with the students and conclude
that the candle burned until it used up all the oxygen, which is one of gases
in air. The water rises about one-fifth of the way up the glass because
oxygen, which is necessary for combustion, makes up about one-fifth of the
gases in air. The gases left in the glass are about four-fifths nitrogen,
with trace amounts of some other gases.
Teacher holds an open bottle of ammonia and lets the students take a waft.
Explain that the pungent odor is ammonia gas that is escaping from the water
in which it is dissolved.
To generate carbon dioxide put about one tablespoon vinegar into a empty
small pop a bottle. Put about three tablespoons baking soda inside a balloon.
Place the open end of the balloon over the top of the bottle. Hold the
balloon so that the baking soda will fall into the bottle. The reaction will
release carbon dioxide gas and the balloon will expand. Discuss with the
students what they observed and conclude that a gas was released and that a
gas takes up space.
Place 1/2 teaspoon into a large test tube. Add about 10 mL of hydrogen
peroxide. Immediately place the open end of the balloon over the open end of
the test tube. There will be a reaction in which oxygen gas is released and
the balloon will inflate. Take the balloon off and tie the open end of
the balloon to keep the gas in the balloon. Take a wooden splint and light it
with a match. Blow out the flame so that the splint is glowing. Insert the
glowing splint into the test tube. The oxygen gas will reignite the splint.
Explain that although oxygen itself will not burn, it is necessary for
Put 1/2 teaspoon powdered sulfur into a crucible. Add 1/2 teaspoon iron
filings. Heat the crucible. Make sure that there is good ventilation,
because an acrid gas will be released in the reaction.
Activity 5 (Optional teacher demonstration )
To make an iodine gas tube place a few iodine crystals into a flask and seal
it with a stopper. Gently heat the flask for about 10 seconds. The crystals
will sublimate and a purplish gas will be visible in the flask. CAUTION:
Iodine gas is poisonous.
To generate hydrogen gas: Place a few zinc chips in the test tube. Add about
5 mL of dilute hydrochloric acid. CAUTION: HYDROCHLORIC ACID IS VERY CAUSTIC.
Cover the test tube to prevent the gas from escaping. Light a match and bring
it close to the test tube's mouth: uncover the test tube. Hydrogen gas was
produced in the reaction between the zinc and hydrochloric acid. This gas is
highly flammable and gives off a characteristic small explosion, when ignited
in a test tube.
Take a shoe box and make cuts in the box to make flaps which can be opened.
Fill the shoe box with small light-weight plastic or styrofoam balls. Use
this to model the Kinetic Molecular Theory. Have the shoe box filled about
three-fourths full with the balls. With the cover off, gently shake the box.
Explain that the although the balls can move, they are restricted. This is
a model of the way the molecules are arranged in a solid. Shake the box
harder, so that the balls will have more motion. Explain that this models
the way the molecules behave in a liquid. Finally open the flaps in the box
and shake the box vigorously. The "molecules" should come out of the box and
spread out. Explain that this models the way gas molecules behave.
Students' responses during the activities and follow-up discussions will be
used as the performance assessment.