Question

following is a list of observations from a chemistry laboratory. place them in the appropriate category. evidence of a chemical change: wax melting, a candle being lit, crushing a rock with a hammer, a car rusting. no evidence for a chemical change: burning toast, water boiling, a white cloudy substance occurs after mixing two clear solutions, leaves changing color in october, yellow and blue paints mixed together

Explanation:

Step1: Recall chemical change criteria

A chemical change results in a new substance with different properties. Physical changes only affect the form or state of a substance without changing its chemical composition.

Step2: Analyze each observation

• Burning toast: Produces new substances like carbon - new chemical compounds are formed, so it's a chemical change.
• Wax melting: Only changes from solid to liquid, same wax substance, physical change.
• A candle being lit: Combustion occurs, new substances like carbon dioxide and water are formed, chemical change.
• Crushing a rock with a hammer: Just changes the size and shape of the rock, no new substances, physical change.
• A white cloudy substance occurs after mixing two clear solutions: Indicates a chemical reaction forming a new substance (precipitate), chemical change.
• A car rusting: Iron reacts with oxygen and water to form iron oxide (rust), new substance, chemical change.
• Leaves changing color in October: Chemical reactions (like breakdown of chlorophyll) occur, new substances are involved, chemical change.
• Yellow and blue paints mixed together: Just a physical mixing of pigments, no new chemical substances are formed, physical change.
• Water boiling: Changes from liquid to gas (water vapor), same water substance, physical change.

Answer:

Evidence of a chemical change: Burning toast, A candle being lit, A white cloudy substance occurs after mixing two clear solutions, A car rusting, Leaves changing color in October.
No evidence for a chemical change: Wax melting, Crushing a rock with a hammer, Yellow and blue paints mixed together, Water boiling.