Unit 2: Practice
Modified True/False
Indicate whether the statement is true or false. If false, change the identified word or phrase to make the statement true.
____
1. There are 6.02  1023 molecules in one mole of water. _________________________
____
2. One mole of ammonia, NH3, is made up one atom of nitrogen and three atoms of hydrogen.
_________________________
____
3. The mass of one formula unit of sodium chloride is the sum of the mass of one sodium ion and one chloride
ion. _________________________
____
4. Avogadro’s number is the number of particles in one mole of any substance. _________________________
____
5. Since atoms are so small, chemists find that it is easier to count the number of particles when doing
experiments. _________________________
____
6. The amount of excess reagent dictates the amount of product formed in a chemical reaction.
_________________________
____
7. In a chemical reaction that involves two reactants, the limiting reagent is identified as the reactant that is
entirely consumed. ______________________________
____
8. If 165.0 g of silver iodide is produced in a reaction for which the theoretical yield is 192.0 g, the percentage
yield is 85.94%. _________________________
____
9. Low yield can be caused by impurities in products. _________________________
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____ 10. Which of the following best describes one mole of potassium sulfate, K2SO4?
a. It contains six atoms in total.
c. It has a molar mass of 174.3 g.
b. It contains one sulfur atom.
d. It contains 3.01 1023 molecules.
____ 11. The molar mass of copper(II) sulfate pentahydrate, CuSO4 5H2O, is
a. 245.6 g/mol
c. 219.2 g/mol
b. 177.5 g/mol
d. 249.6 g/mol
____ 12. The number of carbon atoms present in 0.062 mol acetic acid, HC2H3O2, is
a. 7.5 1022 atoms
c. 1.5 1023 atoms
b. 3.8 1022 atoms
d. 6.0 1023 atoms
____ 13. The number of molecules of hydrogen peroxide found in 3.15 mol H2O2 is
a. 3 molecules
c. 3.80 1023 molecules
b. 1.90 1024 molecules
d. 7.60 1023 molecules
____ 14. The molar mass of a sample of atoms of an element was found to be 107.9 g/mol. This element is likely to be
a. silver
c. magnesium
b. copper
d. oxygen
____ 15. Ammonia is produced from a reaction as shown in the equation 3 H2(g) + N2(g)
2 NH3(g).
The number of moles of hydrogen required to produce 12 moles of ammonia is
a. 1
c. 6
b. 3
d. 18
____ 16. Ethane burns in oxygen to produce carbon dioxide and water. The balanced chemical equation is
2 C2H6 + 7 O2
4 CO2 + 6 H2O. The molar ratio between the ethane and water is
a. 1:2
c. 1:3
b. 2:7
d. 7:4
Short Answer
17. Determine the number of molecules found in 5.00 mol water.
18. Determine the number of carbon atoms found in 2.50 mol methane, CH4.
19. Calculate the number of moles of lead present in 8.6 1017 atoms of Pb.
20. Determine the molar mass of mercury(II) sulfide.
21. Ammonium carbonate is commonly found in smelling salts. Determine the molar mass of (NH4)2CO3.
22. Convert 6.27 mol hydrogen peroxide, H2O2, into mass (in grams).
23. Convert a mass of 89.7 g of lithium hydroxide, LiOH, into an amount in moles.
24. If 4.61 g of gold(I) oxide was the actual yield in a reaction for which the theoretical yield was 8.14 g,
determine the percentage yield.
Problem
25. Potassium chlorate decomposes to form potassium chloride and oxygen gas. What mass of potassium chlorate
is required to form 120.0 g of potassium chloride?
26. Iron(III) oxide can be formed by combining iron and oxygen gas. Determine the mass of iron(III) oxide
produced when 48.2 g of oxygen gas reacts with excess iron.
Unit 2: Practice
Answer Section
MODIFIED TRUE/FALSE
1. T
2. F, one molecule
3. T
4. T
5. F measure moles
use moles
use mass
6. F, limiting
7. T
8. T
9. F, reagents
MULTIPLE CHOICE
10.
11.
12.
13.
14.
15.
16.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
D
A
B
A
D
C
SHORT ANSWER
17. ANS:
There are 3.01  1024 water molecules in 5.00 mol water.
18. ANS:
Since there is one carbon atom in each methane molecule, there are 1.51 1024 atoms of carbon present.
19. ANS:
There is 1.4  106 mol lead present.
20. ANS:
The molar mass of mercury(II) sulfide is 232.7 g/mol.
21. ANS:
The molar mass of ammonium carbonate is 96.11 g/mol.
22. ANS:
The mass of 6.27 mol hydrogen peroxide is 2.13 102 g.
23. ANS:
A mass of 89.7 g of lithium hydroxide is equivalent to 3.74 mol.
24. ANS:
PROBLEM
25. ANS:
balanced equation: 2 KClO3
mole ratio:
2 KCl + 3 O2
KClO3:KCl = 1:1
The mass of potassium chlorate required to produce 120.0 g of potassium chloride is 197.3 g.
26. ANS:
balanced equation: 4 Fe + 3 O2
mole ratio:
2 Fe2O3
O2:Fe2O3 = 3:2
The mass of iron(III) oxide that will be produced is 160 g.