Question

part i - physical vs chemical changes

1. list the types of evidence that a chemical change has taken place
2. which of these is a chemical change?

□) grating cheese
□) melting cheese
□) fermenting cheese
□) mixing two cheeses in a bowl

1. list the types of evidence that a physical change has taken place
2. which of these is not a physical change?

Explanation:

Question 1 (List evidence of chemical change)

Chemical changes involve new substance formation. Evidence includes: 1. Color change (e.g., rusting iron). 2. Gas production (e.g., baking soda + vinegar). 3. Precipitate formation (e.g., mixing solutions with insoluble product). 4. Energy change (heat/light, e.g., burning). 5. Odor change (e.g., rotting food). These indicate a new substance is made.

• Grating cheese: Physical (shape change, no new substance).
• Melting cheese: Physical (state change, solid → liquid, no new substance).
• Fermenting cheese: Chemical (microorganisms create new substances like lactic acid, odor/ taste change).
• Mixing two cheeses: Physical (no new substance, just combining).

So fermenting cheese is chemical.

Physical changes involve no new substance (only state/shape/size change). Evidence: 1. State change (solid ↔ liquid ↔ gas, e.g., melting ice). 2. Shape/size change (cutting, bending). 3. Dissolving (e.g., sugar in water, can be reversed). 4. Mixing (no reaction, e.g., mixing salt and pepper). These preserve the substance’s identity.

Answer:

• Color change
• Gas production (bubbles/fizzing)
• Precipitate (solid) formation
• Energy change (heat, light, sound)
• Odor change (new smell)

Question 2 (Identify chemical change)