HOMEWORK for UNIT 1

HOMEWORK for UNIT 1. Doing science

Significant figures in measurement 1. a. What do the significant figures in a measurement tell you? b. How many digits should you record for a measurement?

2. Report each measurement to the correct number of significant figures. Include units.

13.40 g 5

a. graduated cylinder (mL) b. thermometer (°C) c. digital balance

3. Determine the number of significant figures in each of these measurements: a. 0.723 m b. 8.0 g c. 3,000 µm d. 6.00 x 10–2 g e. 0.0051 L f. 10.50 cm3

4. Determine the number of significant figures in each of these measurements: a. 0.9867 g/mL b. 410 mg c. 1.2300 g d. 7.0 x 10–3 L e. 0.000268 kg f. 24.80 °C

Significant figures in calculations 5. Round off each answer to the appropriate number of significant figures. a. 207.2g12.011g 47.9982g 267.2092g b. 12.4cm 3.8cm 0.6cm 28.272cm3 3 4 .8 2 g g c.  6 .1 0 8 7 7 1 9 3 3 5 .7 c m 3 cm   6. Round off each answer to the appropriate number of significant figures. a. 2 6 . 8 3 g  0 . 9 7 g  2 5 . 8 6 g b. 3 . 8 m  1 2 . 2 m  4 6 . 3 6 m 2  3 6 . 5 1 g g 4 5 . 3 c m c.  8 . 1 3 7 5 m L d.  0 . 8 3 3 9 4 6 9 8 1 c m 8 . 2 m L  7 . 4 m L  9 . 7 c m  5 . 6 c m 

Scientific method 7. a. How is a law different from a theory? b. How is a hypothesis different from a theory? c. Why does the phrase “just a theory” misrepresent scientific knowledge?

8. Classify each of the following as an observation, a law, or a theory: a. A gas is composed of tiny particles in constant random motion. b. When iron rusts in a closed container, the mass of the container and its contents does not change. c. In chemical reactions, mass is conserved (neither gained nor lost). d. When a match burns, heat is released. e. Chlorine is a highly reactive poisonous gas. f. If elements are listed in order of increasing atomic mass, their chemical reactivity follows a repeating pattern. g. The reactivity of elements depends on the arrangement of their electrons. Avogadro’s hypothesis & relative mass 9. a. Describe the experiments that led to Avogadro’s hypothesis. b. State Avogadro’s hypothesis. c. When did Avogadro propose his hypothesis? When did it become widely accepted?

10. The three identical containers illustrated at right contain three different gases at the same temperature and pressure. a. Which contains the largest number of molecules? b. Draw simple circle pictures to illustrate the molecules in the A B C containers. 3.2 g 5.6 g 8.0 g c. Why do the gas samples have different masses? methane nitrogen argon d. What is the relative mass of argon, compared to methane?

The mole and mole conversions 11. The gram is a unit that describes mass, and the meter is a unit that describes length. What does the mole describe?

12. What is the molar mass of a. copper (Cu) b. nitrogen (N2) c. methane (CH4) d. ammonia (NH3)

13. What is the mass of 1.35 mol argon (Ar)?

14. How many moles are in 57 g iron (Fe)?

15. What is the mass of 0.482 mol ammonia (NH3)?

16. How many moles are in 0.0739 g methane (CH4)?

Avogadro’s number and mole conversions 17. a. What is Avogadro’s number? What does it describe? b. How do you decide whether to use molar mass or Avogadro’s number in a mole conversion?

18. How many molecules are in 1.85 moles of nitric oxide (NO)?

19. How many moles are in 34 g mercury (Hg)?

20. What is the mass of 0.204 mol carbon dioxide (CO2)?

21. How many molecules are in 0.477 mol helium (He)?

22. How many molecules are in 13.7 g oxygen (O2)?