Barbara Pawela - Retired

It's a Gas!

Barbara Pawela                   Retired
                                     
                

Objective(s):  
    
    Grades 6-8
  1. To demonstrate that gases are a state of matter.
  2. To generate some gases.
  3. To investigate some properties of gases.
  4. To compare some properties of different gases. 
                                                 
Materials Needed:

     Activity 1           Activity 2            Activity 3         Activity 4
     sound maker          dry yeast             balloons           ammonia
     spray perfume        hydrogen peroxide     vinegar            5 ml HCL
     plastic bags         large test tube       baking soda        a few zinc
     pie pan              balloon               small pop bottles    chips
     small candles        matches               wooden splint      large test
     piece of clay        wooden splint         matches              tube
     tall glass
     matches

Strategy:

     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 safety rules.

  Activity 1      
     Begin the demonstration by asking the students to put their hands about
     12 inches away from their face.  Ask them what they see in the space 
     between their nose and their hands.  Tell the students to wave their hands
     in front of their face.  Discuss and conclude that although they could not
     see the air in front of their face, they could feel the breeze against 
     their skin.
     Spray some perfume.  Ask the students to raise their hands when they smell
     something.  The odor will diffuse and, depending on the distance away from
     the source, the students will raise their hands at intervals.
     Wave a sound tube or use something else to make a sound.  Discuss and 
     conclude that the odor was being diffused; and the sound vibrations 
     were being transmitted through the air.
     Pass out plastic bags (like the ones from the produce section) to each
     group.  Tell the students to wave the bag and scoop the air, and then to 
     close the bag.  Discuss and conclude that air takes up space.
     These demonstrations help to show that although air cannot be seen, it
     can be felt; an odor can be diffused through it; sound vibrations can be
     transmitted through it; and it takes up space.   
     Stick clay pieces on the base of of a candle and on opposite sides of the
     rim of a clear tall glass.  Stand the candle in the pie pan.  Pour water 
     into the pie pan 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 rises.  Discuss and conclude that the 
     candle burned until it used up the oxygen, which is one of the gases in
     air.  The water rises about one-fifth of the way up the glass because
     oxygen, which is necssary 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 other gases.

  Activity 2
    Place 1/2 teaspoon of dry yeast into a large test tube.  Add about 10 ml of
    hydrogen peroxide.  Immediately place the open end of a 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.  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 combustion.

  Activity 3
    To generate carbon dioxide gas put about one tablespoon of vinegar into a 
    small pop bottle.  Put about two tablespoons of baking soda inside a 
    balloon.  Place the open end of the balloon over the top of the bottle.  The 
    reaction will release carbon dioxide gas and the balloon will expand.  
    Repeat the glowing splint test (see Activity 2) by placing the glowing 
    splint into the pop bottle.  The splint goes out and does not burn. 

  Activity 4  (optional teacher demonstration)
    To generate hydrogen gas:  Place a few zinc chips in a test tube.  Add 
    5 mL of dilute hydrochloric acid.  CAUTION: HYDROCHLORIC ACID IS VERY
    CORROSIVE.  Cover the test tube to prevent the gas from escaping.  Light a
    match and bring it close to the mouth of the test tube.  Hydrogen gas is
    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.
    Teacher holds an open bottle of ammonia and lets the students take a weft.
    Explain that the pungent odor is ammonia gas escaping from the water in 
    which it is dissolved.
              
Performance Assessment:

   Students' responses during the activities and follow-up discussions.