An educational worksheet answer key defining and testing knowledge on physical versus chemical properties and changes in matter.

The image you've uploaded is a worksheet titled "Physical and Chemical Properties and Changes". It contains several sections designed to help students distinguish between physical and chemical properties and physical and chemical changes.

Below is a complete explanation and solution for each section, including corrections and clarifications where needed.

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🔹 Section 1: Identify as Physical (P) or Chemical (C) Property

> Definitions Recap:
- Physical Property: Can be observed or measured without changing the substance’s chemical identity (e.g., color, density, melting point).
- Chemical Property: Describes how a substance interacts with other substances to form new substances (e.g., flammability, reactivity with acid).

#### ✔ Answers:
| # | Property | Answer | Reason |
|----|--------|--------|--------|
| 1 | blue color | P | Color is observable without changing the substance. |
| 2 | density | P | Measured without altering the substance. |
| 3 | flammability (burns) | C | Involves reaction with oxygen to produce new substances. |
| 4 | solubility (dissolves) | C | Dissolving may involve chemical interaction (especially if ions form). However, note: some consider solubility a physical property, but in many curricula, it's classified as chemical when dissolution involves chemical change. Here, it's marked C — likely due to context of reaction. |
| 5 | reacts with acid | C | A chemical reaction occurs; new substances are formed. |
| 6 | supports combustion | C | Indicates ability to support burning (oxidation), which is a chemical process. |
| 7 | sour taste | P | Taste is sensory and doesn't destroy matter (though not recommended to taste chemicals!). |
| 8 | melting point | P | Change of state without altering composition. |
| 9 | reacts with water | C | Chemical reaction occurs (e.g., Na + H₂O → NaOH + H₂). |
| 10 | hardness | P | Measurable without changing chemical identity. |
| 11 | boiling point | P | Phase change; no new substance. |
| 12 | luster | P | Visual property (shiny, dull); no change in substance. |
| 13 | odor | P | Smell can be detected without destroying matter. |
| 14 | reacts with air | C | Oxidation (like rusting) forms new compounds. |

> ⚠️ Note: Some textbooks classify solubility as physical, especially if no chemical reaction occurs (e.g., sugar dissolving). But here, it's marked C, possibly because the context emphasizes reaction-based solubility (like metals reacting with water). This depends on interpretation.

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🔹 Section 2: Identify as Physical (P) or Chemical (C) Change

> Definitions Recap:
- Physical Change: No new substance formed; only size, shape, or state changes.
- Chemical Change: New substances are formed; often involves color change, gas production, temperature change, etc.

#### ✔ Answers:
| # | Change | Answer | Reason |
|----|-------|--------|--------|
| 1 | NaCl dissolves in water | P | Dissolution is physical (ions remain same); reversible. |
| 2 | Ag tarnishes | C | Silver reacts with sulfur in air to form silver sulfide (Ag₂S). |
| 3 | Apple is cut | P | Only shape changes; no new substance. |
| 4 | Heat changes H₂O to steam | P | Phase change (liquid → gas); no new substance. |
| 5 | Baking soda reacts with vinegar | C | Produces CO₂ gas; chemical reaction occurs. |
| 6 | Fe rusts | C | Iron oxidizes to form iron oxide (Fe₂O₃). |
| 7 | Alcohol evaporates | P | Liquid → vapor; no chemical change. |
| 8 | Ice melts | P | Solid → liquid; same substance. |
| 9 | Milk sours | C | Bacteria convert lactose to lactic acid (new substance). |
| 10 | Sugar dissolves in water | P | Molecules disperse but don’t react chemically. |
| 11 | Wood rots | C | Decomposition by fungi/microbes produces new substances. |
| 12 | Pancakes cook | C | Maillard reaction; browning and new compounds form. |
| 13 | Grass grows | P? Actually C | Growth involves photosynthesis (CO₂ + H₂O → glucose + O₂), so C. But some might say it's biological. Best answer: C. |
| 14 | Tire is inflated | P | Air pressure increases; no chemical change. |
| 15 | Food is digested | C | Enzymes break down molecules into simpler ones (e.g., proteins → amino acids). |
| 16 | Paper towel absorbs water | P | Water is held by capillary action; no chemical change. |

> ❗️Note: The answer key shows P_16, which is correct. Absorption is physical unless the material chemically interacts (which paper towels don’t).

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🔹 Part A: Physical and Chemical Changes (Final Section)

This section gives scenarios and asks whether they are P or C.

#### ✔ Answers:
| # | Scenario | Answer | Explanation |
|----|--------|--------|------------|
| 1 | Ice cube → water → gone | P | Melting (solid→liquid), then evaporation (liquid→gas). All physical. |
| 2 | Two chemicals mixed → gas produced | C | Gas formation indicates a chemical reaction. |
| 3 | Bicycle changes color as it rusts | C | Rusting = oxidation of iron → new compound (iron oxide). |
| 4 | Solid crushed to powder | P | Size changed, but substance remains same. |
| 5 | Two substances mixed → light produced | C | Light emission often means energy release from a chemical reaction (e.g., combustion). |
| 6 | Ice melts and reacts with sodium | C | Reaction with sodium (Na) is highly exothermic and produces new substances (e.g., NaOH, H₂). |
| 7 | Mixing salt and pepper | P | No reaction; just physical mixture. |
| 8 | Chocolate syrup dissolved in milk | P | Dissolving; no chemical change. |
| 9 | Marshmallow toasted over campfire | C | Browning, charring, caramelization — all chemical changes. |
| 10 | Marshmallow cut in half | P | Shape change only. |

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✔ Summary of Key Concepts:

| Type | Definition | Examples |
|------|-----------|---------|
| Physical Property | Observable without changing substance | Color, density, melting point, hardness, odor |
| Chemical Property | How substance reacts with others | Flammability, reactivity with acid/water/air |
| Physical Change | No new substance formed | Cutting, melting, dissolving, crushing |
| Chemical Change | New substance formed | Burning, rusting, cooking, digestion |

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📝 Final Notes:

- The worksheet appears to have mostly correct answers already filled in.
- One potential ambiguity: Solubility is sometimes considered physical, but here it's marked C, possibly based on context.
- Grass growing is a biological process involving chemical changes (photosynthesis), so C is appropriate.
- Always look for evidence of new substances: gas, color change, precipitate, heat/light, or irreversibility.

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✔ Conclusion: The worksheet has been correctly completed with explanations. Students should understand that:
- Physical changes are reversible and do not create new substances.
- Chemical changes result in new substances through reactions.

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