Chemistry

CHEM& 140 – Checkpoint 1 – Show It Homework Name ______________________________ Section ____

1. The manufacturer of a particular brand of toothpaste claims that the brand contains “no chemicals”. In a few sentences, describe what you think the company means by that statement. Would a scientist consider that statement to be correct? Why or why not?

2. Explain the scientific method. Include definitions, in your own words, for the terms observation, hypothesis, law, and theory.

3. A chemist in an imaginary universe does an experiment that attempts to correlate the size of an atom with its chemical reactivity. The results are tabulated as follows.

Size of Atom Chemical Reactivity

small low

medium intermediate

large high

a. Formulate a law from this data.

b. Formulate a theory to explain the law.

4. What is matter composed of?

5. Classify each property as physical or chemical. To distinguish between physical and chemical properties, consider whether the substance changes composition while displaying the property. If it does not change composition, the property is physical; if it does, the property is chemical.

a. the boiling point of ethanol

b. the temperature at which dry ice sublimes (solid CO2 turns into gaseous CO2)

c. the flammability of ethanol

d. the smell of perfume

e. the tendency of copper to turn green when exposed to air

6. When given a chemical formula of a substance, how can you tell if it represents an element or a compound?

7. Is a compound a mixture or a pure substance?

8. Why do liquids and gases take on the shape of the container they are in but solids do not?

9. Liquid water vaporizes to form steam. Is this a chemical or physical change? Which diagram, a, b, or c, best represents the molecules in steam?

10. Classify each substance as a pure substance or a mixture. If it is a pure substance, classify it as an element or compound. If it is a mixture, classify it as homogeneous or heterogeneous.