1
Temporary (Physical) and Permanent (Chemical) Changes
Objectives:
At the end of the experiment, the students will:
1. Know the difference between physical and chemical changes
2. Give examples of both changes
3. Define the two types of changes
4. Given examples determine whether they are physical or chemical changes.
5. Appreciate that the field of chemistry involves study of matter, their changes and energy that accompanies those changes.
6. Know the signs of a chemical change
Approach Used: 5 e’s or constructivist approach (learning cycle)
· Engage
· Explore
· Explain
· Expand
· Evaluate
Note time shown estimates time involved with students’ interaction).
Materials Needed:
1. Paper
2. Match
3. Raw egg (can be power pt)
4. Cooked egg (can be power pt)
5. Chocolate candy
6. Glass or transparent plastic cup (2 per station)
7. water
8. baking soda
9. raisins
10. plastic spoon
11. Hindenburg balloon explosion on power point.
ENGAGE (5-10 minutes)
Be careful of this demo. Never burn hold the paper with bare hands when lighting it since the paper burns very quickly
Teacher prepares a piece of paper. She tears it in half. Teacher uses a pair of metal tongs to hold up half of this piece of paper and then lights it with a match. Then teacher drops the paper into a bottle and covers it with a plate so no air can get in and stops the burning.
Teacher then asks: After burning the paper, is the burnt part the same as the original paper (show the other half). How do you know? (it is brown). Can you turn the burnt part back to the same paper before? (No. It changed to something else).
Teacher tears up a piece of paper into pieces. Teacher then asks: Is the torn paper same (substance) as paper before. (Yes). How do you know? ( same color and appearance). What is the difference? (different size).
First change is permanent or chemical change. Second one is temporary or physical change.
EXPLORE (10-20 minutes)
Provide the following instructions with the materials in each station:
First part:
1. Fill your glass about 1/2 full with water.
2. Add one teaspoon of baking soda and stir until it is dissolved in the water.
3. Add 5 raisins to the glass.
4. SLOWLY pour in vinegar until the glass is about 3/4 full.
5. Observe what happens
(What they will observe: The vinegar and baking soda react to form carbon dioxide bubbles, and the raisins will dance! The first is an example of chemical change. The dancing raisins prove gas CO2 forms).
Second part: optional and can be as a demo in the explain part to illustrate physical changes or just dissolving two liquids producing mixtures. .
1. Mix 2 tbsps of water with 2 tbsp of vinegar.
2. Add raisins
3. Observe what happens
(they will observe no gas or fizzing and no dancing raisins either. Note water and baking soda without vinegar is also a chem. Rxn and produce fizz. Do not use it as the no rxn example).
EXPLAIN (15-20 MINUTES)
1. What did you observe when you mix baking soda with vinegar? (Fizz or bubbles)
2. What is that fizz? Gas or solid or liquid? (gas)
3. Give me another observation that gas was produced? (the raisins danced)
4. Is that gas which is called carbon dioxide the same as the baking soda and vinegar? (no)
5. Can you transform the gas back to baking soda and vinegar? (no).
6. Why? (Totally different form that escaped).
7. Is the change permanent? (yes)
Do the demo in second part of explore section.
8. What happens when you mixed water and vinegar? No fizz
9. Did the raisins dance? No
10. Is the change permanent? (no)
11. How did you know? (no gas formed)
12. Is water still water and vinegar still vinegar? (yes)
13. Then what happened? (they just mixed or dissolve).
14. What happens when you mix sugar and water? The same
15. Chemistry is field which studies matter and their changes both physical and chemical.
EXTEND (10-15 MINUTES)
1. The teacher shows a piece of chocolate and asks : If you leave this by the window with the sun shining on it. What will happen? (it will melt). Is this permanent or temporary? How can you prove it is temporary? (place in refrigerator and it will harden and will taste chocolate). This is an example of change of state. Solid to liquid. And back also. Others are liquid to gas. And back. Ask then for examples. No eating policy. You can distribute small piece of candy per child after clean up.
2. Show students uncooked eggs and cooked egg. Ask them to describe what they see. One is liquidy, other hard. Is this permanent. How do you know? Can you get back the raw egg back? Is this the same as the chocolate melting? (no)
3. Show students clean nail and rusty nail. Ask them to describe what they see?
a. Different color
b. Crusty
4. Show a picture of an explosion Hinderberg baloon. What do they observe? Fire. Why? hydrogen combustible and heat made it burn. Point out chemistry is also involved in studying the energy accompanying the changes.
EVALUATE (15-20 MINUTES)
1. Ask the students the difference between permanent and temporary change?
2. Ask them what are the signs that a permanent change has occurred? What do they observe? Give examples of such indicators. (I found out this question is too abstract for the children and only got blank looks. It is probably better to ask again what did you observe in the dancing raising activity. Answer gas forming. What happens when a nail rust, what do you see? Answer solid kalawang. Etc etc and then summarize that these are indicators for chemical change.
· Gas forming (dancing raisin)
· Solid or precipitate forming (egg and rust in nail)
· Drastic color change (burning paper and rust)
· Heat produced. (explosion)
3. Ask them for other examples or give more examples and ask them to classify.
· Ice melting (physical
· Leaves turning brown (chemical)
· Cooking gas burning (chemical)
· Mixing coffee and milk
4. What is chemistry? Field that studies matter and their physical and chemical changes and energy that accompanies them.
Notes:
1. Be sure that the examples are appropriate for the age and background of the students. Have they been exposed to the example already?
2. Some of the examples in the Extension part can be part of the Explore part if you have time and the resources or can be a demo done by the teacher rather than a before and after or show and tell only. It can also be in the Engage part but I found that my nine year old niece had a hard time when asked to what happens when eggs are cooked for some reason. For older kids, one can ask in the Engage part for things they observe their mother do in the kitchen. Cook eggs for example and do they observe. Mix coffee with water. Etc. I find this a little bit too complicated with my niece who had never cooked before.
3. The reason the students have a hard time determining whether it is a physical or chemical change is because they do not actually have eyes that can see that new compounds with different formulas from reactants are produced. They have to use indirect evidence using the signs and common sense and experience when given examples on paper during exams.
4. Some instructors prefer to skip the classification of matter and uses the approach of showing atoms when making mixtures (physical change) and compounds (chemical change) on transparencies or video.