Practice exam #1 Key 9/19/06

1. Refer to Table 1.3. Which of the following represents the largest mass? A. 2.0 x 102 mg B. 0.0010 kg C. 1.0 x 105 μg D. 2.0 x 102 cg

2. Carry out the following unit conversions

(1 gallon = 4 quarts, 1 L = 0.26 gal, 1 mile = 5280 feet, 1 foot = 0.30 meters, 1 minute = 60 seconds, 1 hour = 60 minutes)

A. 325 mg to kg 3.25 x 10-4 kg B. 3.7 L to quarts 3.8 qt

C. 57 miles per hour to kilometers per second 2.5 x 10-2 kps

3. Bromine is a red liquid at 25°C. Its density is 3.12g/cm3. What is the volume of 28.1 g of liquid bromine? 9.01 cm3

You will need to know the density equation! Density = mass/volume.

4. Radio waves travel at the speed of light, which is 3.00 x 108 m/s. How many minutes does it take for a radio message to reach earth from Mars if Mars is 9.9 x 107 km from Earth? 5.5 min.

Did you get 0.18 for the answer? You were warm…what were the units?

5. How many protons and electrons are contained in the following species?

A. Magnesium ion (Mg2+) 12 p 10 e B. Calcium atom (Ca) 20 p 20 e

C. Chloride ion (Cl-) 17 p 18 e

6. (Multiple choice) What percentage of the mass of a carbon-12 atom is contributed by its electrons? (The mass of an electron is 5.45 x 10-4 amu.)

A. 0.027% Could you have done this if it wasn’t mult choice? B. 6.0% C. 33.0% D. 50.0% E. 99.97%

7. Name the following molecules. (Refer to Table 2.3 in the text.)

A. NH4NO3 ammonium nitrate (recognize ammonium as a common cation) B. N2O4 dinitrogen tetroxide (or dinitrogen tetraoxide)

C. Fe3(PO4)2 iron (II) phosphate

8. The molecular formula of caffeine, the active ingredient in many popular morning beverages, is C8H10N4O2.

A. What is the molecular mass of caffeine? 1.942 x 102 amu

B. What is the molar mass of caffeine? 1.942 x 102 g

C. What is the empirical formula of caffeine? C4H5N2O

9. One nanogram seems like a very small amount. How many magnesium (Mg)

atoms are there in 1.00 ng of Mg? 2.48 x 1013 atoms

10. Boron obtained from borax deposits in Death Valley consists of two isotopes: boron-10 and boron-11 with atomic masses of 10.013 amu and 11.009 amu, respectively. The atomic mass of boron is listed on the periodic table as 10.81 amu. Calculate the natural abundances of these two isotopes.

Boron-10: 20% Boron-11: 80%

Remember: the equation for this problem will not be given to you on exam day.

11. What is the empirical formula of a compound of uranium (U) and fluorine (F) that is composed of 67.6% U and 32.4% F (by mass)? UF6

Can you go backwards (ie. from empirical formula to percent composition)?

12. Ammonia (NH3) reacts with diatomic oxygen (O2) to form nitrogen oxide (NO) and water vapor (H2O):

A. Represent this reaction with a balanced equation. 4NH3 + 5O2 → 4NO + 6H2O

B. When 20.0 g NH3 and 50.0 g of O2 are allowed to react, which is the

limiting reagent? NH3

C. When 20.0 g NH3 and 50.0 g of O2 are allowed to react, what is the mass of nitrogen oxide produced? 3.54 x 101 g