Question

part b: each each scenario. decide whether a physical or chemical change has occurred and give evidence for your answer. the first one has been done for you to use as an example.

scenario	physical or chemical change?	evidence
2. your bread has been in the toaster too long. the bread is black and the toaster is full of smoke.
3. you forget to dry the bread knife when you washed it and reddish - brown spots appeared on it.
4. you blow dry your wet hair.
5. in baking biscuits and other quick breads, the baking powder reacts to release carbon dioxide bubbles. the carbon dioxide bubbles cause the dough to rise.
6. you take out your tooth - size spoons and notice that they are very dull and have some black spots.
7. a straight piece of wire is coiled to form a spring.
8. food color is dropped into water to give it color.
9. chewing food to break it down into smaller particles represents a _ change, but the changing of starch into sugars by enzymes in the digestive system represents a _ change.
10. in a fireworks display, the fireworks explode giving off heat and light.

part c: true (t) or false (f)

2. in a physical change, the nature of matter is changed.
3. evaporation occurs when liquid water changes into a gas.
4. burning is a physical change.
5. rusting would be a physical change.
6. combining hydrogen and oxygen to make water is a physical change.
7. breaking up concrete is a physical change.
8. sand being washed out to sea from the beach is a chemical change.
9. any non - changing a chemical change occurs.
10. and non - changing a marble statue is a physical change.

Explanation:

1. Scenario 1: A student removes a leaf or branch from the tree. Physical change. Evidence: No new substance formed, just a change in the physical state of the plant part being separated.
2. Scenario 2: Yeast in bread dough makes it rise too much and the bread is black in the toaster. Chemical change. Evidence: The yeast causes fermentation (a chemical reaction) and the black - ening is due to burning (oxidation, a chemical change).
3. Scenario 3: You forget to dry the bread knife and rust spots appear. Chemical change. Evidence: Rust (iron oxide) is formed through a chemical reaction between iron in the knife, oxygen, and water.
4. Scenario 4: You blow dry your wet hair. Physical change. Evidence: Water changes from liquid to gas (evaporation), no new substance is formed.
5. Scenario 5: In baking biscuits and other quick - breads, the baking powder reacts to release carbon dioxide bubbles. Chemical change. Evidence: A chemical reaction occurs between baking powder components to produce carbon dioxide gas.
6. Scenario 6: You take out your tooth - size spoons and notice they are very dull and have some black spots. Chemical change. Evidence: Oxidation or tarnishing (a chemical reaction) causes the dullness and black spots.
7. Scenario 7: A straight piece of wire is coiled to form a spring. Physical change. Evidence: Only the shape of the wire changes, no new chemical substance is formed.
8. Scenario 8: Food color is dropped into water to give it color. Physical change. Evidence: The food color dissolves in water, no chemical reaction occurs, just a physical mixing.
9. Scenario 9: Chewing food to break it down into smaller particles represents a physical change, but the changing of starch into sugars by enzymes in the digestive system represents a chemical change.
10. Scenario 10: In a fireworks display, the fireworks explode giving off heat and light. Chemical change. Evidence: Chemical reactions occur in the fireworks to produce heat, light, and new substances.

Part C:

1. False. Changing the size and shape of a piece of wood is a physical change as no new substance is formed.
2. False. In a physical change, the nature of matter is not changed, only its physical properties like shape, size, state may change.
3. True. Evaporation occurs when liquid water changes into a gas.
4. True. This is a physical change as it involves a change in state.
5. False. Burning is a chemical change as new substances are formed.
6. False. Combining hydrogen and oxygen to make water is a chemical change as a new compound (water) is formed.
7. False. Burning a marshmallow is a chemical change as it involves oxidation and the formation of new substances.
8. False. Salt being washed out to sea from the beach is a physical change (dissolving), no new substance is formed.
9. False. An iron nail rusting is a chemical change as iron oxide is formed.
10. False. An ant - stinging a marble statue is a physical interaction (mechanical damage), not a chemical change.

Answer:

Scenario	Physical or Chemical Change	Evidence
2	Chemical change	Fermentation and burning (oxidation)
3	Chemical change	Rust (iron oxide) formation
4	Physical change	Evaporation of water
5	Chemical change	Production of carbon dioxide gas
6	Chemical change	Oxidation or tarnishing
7	Physical change	Only shape change of wire
8	Physical change	Dissolving of food color
9	Physical (chewing) and Chemical (starch - sugar conversion)	Chewing is particle - size change, enzyme - starch reaction
10	Chemical change	Chemical reactions in fireworks
Part C - 1	False	No new substance in wood shape - size change
Part C - 2	False	Matter nature unchanged in physical change
Part C - 3	True	Liquid to gas change in evaporation
Part C - 4	True	State change is physical
Part C - 5	False	Burning forms new substances
Part C - 6	False	New compound (water) formed
Part C - 7	False	Burning marshmallow forms new substances
Part C - 8	False	Dissolving (physical) of salt
Part C - 9	False	Iron oxide formation in rusting
Part C - 10	False	Ant - statue interaction is physical