(Bold items will be written on the board, and students copy everything from the board into their notes.)

 

MON   26-10-04   11:10-12:20   FORM 1

 

Changing State

            3b Matter 2, pp. 24-25 text; p. 5 syllabus; p. 116 GCSE book

 

Objectives:

• Demonstrate how matter can be changed from one state to another.
• Find out how solids, liquids, and gasses change state.
• Understand each change of state, including melting, evaporation, boiling, solidification/freezing, condensation, and sublimation.

 

Previous knowledge:

• ALOUD- Q: “What happens when you leave solid ice in the sun?”
• STUDENTS: “It melts.” (It changes from solid to liquid state.)
• ALOUD- Q: What happens when a puddle is exposed to the sun’s heat?”
• STUDENTS: “It evaporates.  It disappears.”  (It changes from liquid to gas state.)                   
• ALOUD- Note: “It does not boil!”

 

Solid

Teaching Materials:

·          Diagram to be drawn on board:

 

        Melting        

Freezing/                            Sublimation

         Solidification

          

    

Gas

Liquid

Evaporation

      

     Condensation

 

• Demonstration materials:
• Small piece of wax (candle), Test tube
• Beaker (cover the rim with dampened cotton), Water
• Bunsen burner, Matches
• Tripod, Gauze
• Evaporating dish
• Ammonium Chloride (crystals) in a test tube
• Heat tongs for heated test tubes and for heated beaker
• Test tube rack

 

Teacher/Learner Activities:

1. Briefly study and discuss the diagram on the board.
2. During the demonstrations, write down observations in your notes using the terms in the diagram. 
3. The teacher will do the demonstrations using the demonstration materials, and the students will crowd around to observe.  The teacher will guide students’ observations and ask them what they see throughout. 
1. Turn on the gas and light the Bunsen burner with a match.  Adjust the flame.
2. Gently heat a solid piece of wax in a test tube over the Bunsen burner flame, using the heat tongs to hold the test tube, until it becomes a liquid.            

MELTING

3. Place the test tube containing the liquid wax in the test tube rack to use later.  The wax would have started to evaporate if it had continued to heat.
4. Set the tripod above the Bunsen burner flame and place the gauze on top.  Place the water-filled beaker on top of the gauze. 
5. While waiting for the water to boil:

                                                               i.      Remind students to pay attention, and ask them what will happen.

                                                             ii.      Refer to the diagram on the board.

                                                           iii.      Ask students to differentiate between evaporation and boiling, and write the answer on the board.

1.        EVAPORATION occurs at the surface of a liquid, and boiling is not necessary.

2.       BOILING occurs throughout the liquid, as you can see by the bubbles.  The bubbles escape into the air at the surface, so evaporation is still occurring.

6. The water should be boiling or vapor should be escaping.  Whether or not this is true, place the evaporating dish on top of the beaker.
7. Point out the water vapor escaping from the beaker.                                                      EVAPORATION
8. Point out the bubbles produced from the steady boil.                                        BOILING
9. Point out the liquid collecting on the evaporation dish and on the sides of the beaker.  Lift up the evaporating dish to show the students.                                       CONDENSATION
10. Gently heat the ammonium chloride crystals in the test tube over the Bunsen burner flame, using the heat tongs to hold the test tube, until it changes state.
11. Ask students to observe carefully!  The ammonium chloride will become a gas without becoming a liquid.  When students can see the gas clearly, ask individual students to peer at the tube and into the tube to see if any liquid is present.  They will not see any liquid.                                                                 SUBLIMATION
12. Pick up the tube with the wax again, and show students.  It should be solid.                  SOLIDIFICATION/FREEZING
3. Review the observed changes in state, combined with additional information.
1. Ask students what happened to the candle wax. 

                                                               i.      It melted.  Then it solidified/froze.

2. Ask students what happened water in the beaker. 

                                                               i.      It evaporated.  It boiled.  It condensed on the evaporating dish and on the beaker.

3. Ask students what happened to the ammonium chloride crystals.

                                                               i.      They sublimed.

4. Give students additional information, possibly by asking for their responses.

                                                             i.      Evaporation can occur at different temperatures.

1.        Boiling is not necessary.

2.       Different substances evaporate/boil at different temperatures.

                                                           ii.      Each substance has a unique melting and boiling point.

                                                           iii.      A substance boils and condenses at the same temperature, depending whether it is warming or cooling.  (@ 100 degrees Celsius for water)

                                                            iv.      A substance melts and freezes/solidifies at the same temperature, depending whether it is warming or cooling.  (@ 0 degrees Celsius for water)

                                                              v.      Draw a picture of dry ice (carbon dioxide) on the board, and explain it.  We use it in MI.  It is an example of sublimation at room temperature.  In contrast, the ammonium chloride had to be heated in order to sublime. 

                                                            vi.      Iodine crystals and Naphthalene balls are examples of sublimation.

 

Core Points:

• Substances can change state by warming or cooling.
• Changes in state include melting, evaporation, boiling, solidification/freezing, condensation, and sublimation.

 

Evaluation:  Write on Board!    12 POINTS Begin to mark in class.