Chapter 2 & 3 Test Review
*Make sure you are familiar with using significant digits in all your calculations. ;
*Make sure you are able to calculate molar mass.
*Always report the units on a calculation.
Isotopes / average atomic mass:
1. Suppose carbon-12 has a natural abundance of 99.00%. The existence of carbon-13 has been
confirmed at a natural abundance of 1.00%. What average atomic mass should be reported for carbon?
2. Rubidium has two isotopes: rubidium-85 (84.91u) and rubidium-87 (86.91u). If the average atomic
mass of rubidium is 85.47 u. Determine the percentage abundance of each isotope.
Converting between mass, moles, volume, molecules, atoms.
3. How many grams are in 43.6 L of oxygen gas?
4. How many nitrogen atoms are in 28.35 g of dinitrogen monoxide?
5. Suppose you have 2.6 mol of water. How many grams of water do you have?
b. Calculate the total number of atoms in this quantity of water.
6. Calculate the number of formula units in 5.62 g of Iron (III) oxide.
Percentage composition, Empirical formula, molecular formula
7. The chemical formula for sugar is C6H12O6. What is the percentage composition of sugar by mass?
8. Calculate the mass percentage of hydrogen in H2SO4
9. Bauxite is a pure mineral containing aluminum in the form of Al(OH)3. The aluminum can be
extracted from this mineral but it is very expensive. This is why it is important to recycle aluminum
materials.
a. Calculate the mass percentage of aluminum in bauxite.
b. From 957 g of bauxite what mass of aluminum could you expect to collect?
10. Calculate the empirical formula of a compound that contains 83.21% carbon and 16.79% hydrogen.
Use table 3.2 on page 90 to help you determine the factor to multiply.
11. Codeine has a molar mass of 299.39 g/mol. It is used as a mild painkiller in the medical field. The
mass percent of codeine determined by mass spectrometer is….
72.21 % C
16.03% O
7.08% H
4.68% N
Determine the molecular formula for codeine.
12. Octane is an important chemical component in gasoline. It aids in creating a smooth combustion
process to improve fuel efficiency and reduce undesired denotation in the engine. The empirical
formula of octane is C4H9. Determine the molecular formula If the molar mass of octane is 114.26 g/mol
Answers:
1. 12.01
2. Rb-85 abundance 72%
Rb-87 abundance 28%
3. 62.3 g O2
4. 7.758 x 1023 atoms N
5. a) 47 g H2O
b) 4.7 x 1024 atoms
6. 2.12 x 1022 F.U.
7. C: 40.00% H: 6.73% O: 53.27%
8. 2.06% H
9. a) 34.56% Al
b) 331 g Al
10. C5H12 *This question was made up quickly so it requires a factor of 5 to be used. I will make sure on
a test you would only need to multiply by 2 or 3 to get the final answer.
11. C18H21NO3 *No multiplying needed.
12. C8H18