Question

description identify and describe the following changes as either physical p or chemical c and provide an explanation
nacl (table salt) dissolves in water. explanation
milk sours.
baking soda reacts to vinegar
ag (silver) tarnishes.
grass grows.
sugar dissolves in water.
fe (iron) rusts.
an apple is cut.
a tire is inflated.
wood rots.
alcohol evaporates.
heat changes h2o to steam.
food is digested.
pancakes cook.
ice melts.
paper towel absorbs water.
p/c item identify the following changes as either physical p or chemical c and provide an explanation

1. an ice cube is placed in the sun. later there is a puddle of water. later still the puddle is gone.
2. two chemicals are mixed together, and a gas is produced.
3. a bicycle changes color as it rusts.
4. a solid is crushed to a powder.
5. two substances are mixed, and light is produced.
6. a piece of ice melts and reacts with sodium.
7. mixing salt and pepper.
8. chocolate syrup is dissolved in milk.
9. a marshmallow is toasted over a campfire.
10. a marshmallow is cut in half.

iii. essay writing question

1. list at least three physical properties of tap water.
2. explain why the mass of an object cannot help you identify what material the object

Explanation:

Step1: Recall physical and chemical change definitions

Physical change: no new substances formed, change in state or appearance. Chemical change: new substances formed.

Step2: Analyze "NaCl (Table Salt) dissolves in water"

P. No new substance formed, just salt dispersed in water.

Step3: Analyze "Milk sours"

C. Bacteria cause chemical reactions, new sour - tasting substances formed.

Step4: Analyze "Ag (Silver) tarnishes"

C. Silver reacts with sulfur - containing compounds in air, new silver sulfide formed.

Step5: Analyze "Sugar dissolves in water"

P. No new substance, sugar molecules disperse in water.

Step6: Analyze "An apple is cut"

P. No new substance, just change in shape.

Step7: Analyze "Wood rots"

C. Microorganisms cause chemical breakdown, new substances formed.

Step8: Analyze "Heat changes H2O to steam"

P. Change of state from liquid to gas, no new substance.

Step9: Analyze "Pancakes cook"

C. Chemical reactions due to heat, new substances formed.

Step10: Analyze "Baking soda reacts to vinegar"

C. Produces carbon dioxide gas and other new substances.

Step11: Analyze "Grass grows"

C. Complex chemical processes involving photosynthesis and growth, new substances formed.

Step12: Analyze "Fe (Iron) rusts"

C. Iron reacts with oxygen and water, new iron oxide formed.

Step13: Analyze "A tire is inflated"

P. Air is added, no new substance formed.

Step14: Analyze "Alcohol evaporates"

P. Change of state from liquid to gas, no new substance.

Step15: Analyze "Food is digested"

C. Chemical reactions break down food into new substances.

Step16: Analyze "Ice melts"

P. Change of state from solid to liquid, no new substance.

Step17: Analyze "Paper towel absorbs water"

P. Physical absorption, no new substance.

Step18: Analyze "An ice cube is placed in the sun. Later there is a puddle of water. Later still the puddle is gone"

P. Melting and evaporation, change of state, no new substance.

Step19: Analyze "Two chemicals are mixed together, and a gas is produced"

C. New substance (gas) formed.

Step20: Analyze "A bicycle changes color as it rusts"

C. Rusting is a chemical reaction forming new iron - oxide, color change is a sign of chemical change.

Step21: Analyze "A solid is crushed to a powder"

P. Change in physical form, no new substance.

Step22: Analyze "Two substances are mixed, and light is produced"

C. Chemical reaction causing light production, new substances formed.

Step23: Analyze "A piece of ice melts and reacts with sodium"

C. Melting is physical, but reaction with sodium is chemical, producing new substances.

Step24: Analyze "Mixing salt and pepper"

P. No chemical reaction, just physical mixing.

Step25: Analyze "Chocolate syrup is dissolved in milk"

P. No new substance, just dispersion.

Step26: Analyze "A marshmallow is toasted over a campfire"

C. Chemical reactions due to heat, new substances formed.

Step27: Analyze "A marshmallow is cut in half"

P. Change in shape, no new substance.

Step28: Answer for "List at least three physical properties of tap water"

Colorless, odorless, liquid at room - temperature.

Step29: Answer for "Explain why the mass of an object cannot help you identify what material the object"

Mass is an extensive property that depends on the amount of matter. Different materials can have the same mass, and the same material can have different masses depending on its amount. We need intensive properties like density, melting point for identification.

Answer:

1. NaCl (Table Salt) dissolves in water: P, no new substance formed, just salt dispersed in water.
2. Milk sours: C, bacteria cause chemical reactions, new sour - tasting substances formed.
3. Ag (Silver) tarnishes: C, silver reacts with sulfur - containing compounds in air, new silver sulfide formed.
4. Sugar dissolves in water: P, no new substance, sugar molecules disperse in water.
5. An apple is cut: P, no new substance, just change in shape.
6. Wood rots: C, microorganisms cause chemical breakdown, new substances formed.
7. Heat changes H2O to steam: P, change of state from liquid to gas, no new substance.
8. Pancakes cook: C, chemical reactions due to heat, new substances formed.
9. Baking soda reacts to vinegar: C, produces carbon dioxide gas and other new substances.
10. Grass grows: C, complex chemical processes involving photosynthesis and growth, new substances formed.
11. Fe (Iron) rusts: C, iron reacts with oxygen and water, new iron oxide formed.
12. A tire is inflated: P, air is added, no new substance formed.
13. Alcohol evaporates: P, change of state from liquid to gas, no new substance.
14. Food is digested: C, chemical reactions break down food into new substances.
15. Ice melts: P, change of state from solid to liquid, no new substance.
16. Paper towel absorbs water: P, physical absorption, no new substance.
17. An ice cube is placed in the sun. Later there is a puddle of water. Later still the puddle is gone: P, melting and evaporation, change of state, no new substance.
18. Two chemicals are mixed together, and a gas is produced: C, new substance (gas) formed.
19. A bicycle changes color as it rusts: C, rusting is a chemical reaction forming new iron - oxide, color change is a sign of chemical change.
20. A solid is crushed to a powder: P, change in physical form, no new substance.
21. Two substances are mixed, and light is produced: C, chemical reaction causing light production, new substances formed.
22. A piece of ice melts and reacts with sodium: C, melting is physical, but reaction with sodium is chemical, producing new substances.
23. Mixing salt and pepper: P, no chemical reaction, just physical mixing.
24. Chocolate syrup is dissolved in milk: P, no new substance, just dispersion.
25. A marshmallow is toasted over a campfire: C, chemical reactions due to heat, new substances formed.
26. A marshmallow is cut in half: P, change in shape, no new substance.
27. Physical properties of tap water: Colorless, odorless, liquid at room - temperature.
28. Mass cannot identify material: Mass is an extensive property that depends on the amount of matter. Different materials can have the same mass, and the same material can have different masses depending on its amount. We need intensive properties like density, melting point for identification.