Base your answers to questions 1 through 3 on the particle diagrams below, which show atoms and/or molecules in three different samples
of matter at STP.
1. Explain why (x)(x) does not represent a compound.
2. When two atoms of y react with one atom of z, a compound forms. Using the number of atoms shown in sample 2, what is the maximum
number of molecules of this compound that can be formed?
3. Which sample represents a pure substance?
4. Base your answer to the following question on the
information below, which describes the smelting of iron
ore, and on your knowledge of chemistry.
In the smelting of iron ore, Fe2O3 is reduced in a blast
furnace at high temperature by a reaction with carbon
monoxide. Crushed limestone, CaCO3, is also added to
the mixture to remove impurities in the ore. The carbon
monoxide is formed by the oxidation of carbon(coke), as
shown in the reaction below:
2 C + O2 - 2 CO + energy
Liquid iron flows from the bottom of the blast furnace
and is processed into different alloys of iron.
Balance the equation for the reaction of Fe2O3 and CO
using the smallest whole-number coefficients.
5. In a laboratory experiment, a student determined the mass of the product, NaCl(s), to be 1.84 grams.
a Calculate the gram formula mass of NaCl(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all work.
Indicate the correct answer, including an appropriate unit.]
b Calculate the number of moles of NaCl(s) produced. Show all work. Indicate the correct answer.
6. Base your answers to the following questions on the information below.
Sodium is an essential ingredient in the human diet.The Federal Food and Drug Administration recommends that
the average adult daily requirement for sodum is 2.4 grams. Sodium is ingested through consuming plant and
animal tissues, but another good source is table salt, sodium chloride.
a) Write the chemical formula of sodium chloride.
b) What is the gram-formula mass of a mole of sodium chloride?
c) How many moles of table salt, sodium chloride would need to be comsumed in order to ingest the 2.4 grams? [Show all work]
7. Given the unbalanced equation:
__Ca(ClO3)2 → __CaCl2 + __O2
balance the equation using smallest whole number
coefficients.
8. In a laboratory experiment, a student determined the mass of the product, NH4NO3(s), to be 7.89 grams.
a. Calculate the gram formula mass of NH4NO3(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all
work. Indicate the correct answer in proper significant figures and include an appropriate unit.]
b. Calculate the number of moles of NH4NO3(s) produced. [Show all work.
Indicate the correct answer in proper significant figures.]
9. Given the equation:
2H2(g) + O2(g) - 2H2O(g)
If 8.0 moles of O2 are completely consumed, what is the
total number of moles of H2O produced?
Base your answers to questions 10 through 12 on the information and equation below.
Antacids can be used to neutralize excess stomach acid. Brand Aantacid contains the acid-neutralizing agent magnesium
hydroxide, Mg(OH)2. It reacts with HCl(aq) in the stomach, according to the following balanced equation:
2 HCl(aq) + Mg(OH)2(s) → MgCl2(aq) + 2 H2O(…)
10. Show a correct numerical setup for calculating the number of moles of Mg(OH)2 (gram-formula mass = 58.3 grams/mole) in an 8.40gram sample.
11. If a person produces 0.050 mole of excess HCl in the stomach, how many moles of Mg(OH)2 are needed to neutralize this excess
hydrochloric acid?
12. Brand B antacid contains the acid-neutralizing agent sodium hydrogen carbonate. Write the chemical formula for sodium hydrogen
carbonate.
13. What is the gram-formula mass of (NH4)2CO3? Use
atomic masses rounded to the nearest whole number.
Base your answers to questions 14 and 15 on the unbalanced equation provided:
___ C5H12(g) + ___ O2(g) → ___ CO2(g) + ___ H2O(g)
14. Balance the equation using the smallest whole-number coefficients.
15. Using your balanced equation, show a correct numerical setup for calculating the total number of moles of H2O(g) produced when 5.0
moles of O2(g) are completely consumed.
16. Base your answers to the following questions on the information below.
Rockets use as fuel, liquid hydrogen, H2(l) and liquid oxygen , O2(l) , which react together forming hot gaseous
water. This reaction provides the energy to lift the the shuttle and it's crew.
Write a balanced equation for the reaction of liquid hydrogen with liquid oxygen to produce gaseous water. Include the energy term
( " + energy" ) in your equation.
17. In a laboratory experiment, a student determined the mass of the product, KNO3(s), to be 19.8 grams.
a Calculate the gram formula mass of KNO3(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all
work. Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of KNO3(s) produced. [Show all work. Indicate the correct answer in proper significant figures.]
18. A student heats a 243 gram sample of BaCl2 • 2H2O hydrated crystals?
a What was the percentage by mass of water in the hydrated crystals?[Show all work]
b If all the water was driven out of the crystal, what would be the expected weight of the BaCl2 sample remaining?[Show all work]
Base your answers to questions 19 and 20 on the information below.
Gypsum is a mineral that is used in the construction industry to make drywall (sheetrock). The chemical formula for
this hydrated compound is CaSO4 • 2 H2O. A hydrated compound contains water molecules within its crystalline
structure. Gypsum contains 2 moles of water for each 1 mole of calcium sulfate.
19. Show a correct numerical setup for calculating the percent composition by mass of water in this compound and record your answer.
20. What is the gram formula mass of CaSO4 • 2 H2O?
21. Given the unbalanced equation:
__Fe2O3(s) + __CO(g) → __Fe(l) + __CO2(g)
Balance the equation using smallest whole number
coefficients.
22. Base your answers to the questions below on the following information:
Ethene reacts with oxygen in a combustion reaction as shown by the chemical equation below:
C2H4 +
O2 → 2 CO2 + 2 H2O + Heat
a In order for the equation to be balanced, what coefficient should the oxygen have?
b What is the mole ratio of ethene to water?
c How many moles of oxygen are needed if 2.5 moles of ethene are combusted?
d Is this an exothermic or endothermic reaction? Explain your answer.
23. Given the unbalanced equation:
__Al(OH)3 + __H2SO4 → __Al2(SO4)3 + __H2O
Balance the equation using smallest whole number
coefficients.
Base your answers to questions 24 through 26 on the balanced chemical equation below.
2 H 2O → 2 H 2 + O 2
24. What type of reaction does this equation represent?
25. How does the balanced chemical equation show the Law of Conservation of Mass?
26. What is the total number of moles of O2 produced when 8 moles of H2O is completely consumed?
27. Base your answers to the following questions on the information below.
For health reasons, the element chlorine is added to the drinking water because it will kill disease-causing
organisms. Typically 0.50 ppm of chlorine is added to drinking water to make it safe.
In 2.0 liters of drinking water (2000.g), how many grams of chlorine is present?[Show all work. Include in your answer proper
units and significant figures.]
28. In a laboratory experiment, a student determined the mass of the product, KClO3(s), to be 45.7 grams.
a. Calculate the gram formula mass of KClO3(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all
work. Indicate the correct answer in proper significant figures and include an appropriate unit.]
b. Calculate the number of moles of KClO3(s) produced. [Show all work. Indicate the correct answer in proper significant figures.]
29. Given the unbalanced equation:
__Li + __N2 → __Li3N
balance the equation using smallest whole number
coefficients.
30. Given the compound C4H10O8,
a Calculate the molar masss of the compound.
b
Calculate the number of moles in 17.7 grams of the compound.
c
What is the empirical formula for this compound?
31. Show a correct numerical setup for calculating the
number of moles of CO2 (gram-formula mass = 44
g/mol) present in 11 grams of CO2.
32. In a laboratory experiment, a student determined the mass of the product, CaCl2(s), to be 45.5 grams.
a Calculate the gram formula mass of CaCl2(s). Round atomic masses from the Periodic Table to the nearest tenth. [ Show all work.
Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of CaCl2(s) produced. [Show all work. Indicate the correct answer in proper significant figures.]
33. In a laboratory experiment, a student determined the mass of the product, HgBr(s), to be 98.7 grams.
a Calculate the gram formula mass of HgBr(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all work.
Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of HgBr(s) produced. [ Show all work. Indicate the correct answer in proper significant figures.]
34. The following procedures are carried out during a laboratory activity to determine the mass in grams of CuSO4 in a hydrated sample
of CuSO4•5H2O.
Step 1 Determine the mass in grams of the crucible and CuSO4•5H2O.
Step 2 Determine the mass in grams of the crucible and CuSO4
Step 3 Determine the mass in grams of CuSO4•5H2O.
Step 4 Determine the mass in grams of the empty crucible.
Step 5 Determine the mass in grams of CuSO4
Arrange the steps above in the order that the student should use to determine the mass of CuSO4 in the sample.
_______, _______, _______, _______, ________
35. In a laboratory experiment, a student determined the mass of the product, KI(s), to be 4.66 grams.
a Calculate the gram formula mass of KI(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all work.
Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of KI(s) produced. [Show all work. Indicate the correct answer in proper significant figures.]
36. In a laboratory experiment, a student determined the mass of the product, NH4Cl(s), to be 0.372 grams.
a Calculate the gram formula mass of NH4Cl(s). Round atomic masses from the Periodic Table to the nearest tenth. [ Show all
work. Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of NH4Cl(s) produced. [Show all work. Indicate the correct answer in proper significant figures.]
37. Given the unbalanced equation:
__Al2(SO4)3 + __Ca(OH)2 → __Al(OH)3 + __CaSO4
Balance the equation using smallest whole number
coefficients.
38. Given the unbalanced equation:
__Al2(SO4)3 + __ZnCl2 → __AlCl3 + __ZnSO4
balance the equation using smallest whole number
coefficients.
39. In a laboratory experiment, a student determined the mass of the product, CaSO4(s), to be 31.9 grams.
a Calculate the gram formula mass of CaSO4(s). Round atomic masses from the Periodic Table to the nearest tenth. [Show all
work. Indicate the correct answer in proper significant figures and include an appropriate unit.]
b Calculate the number of moles of CaSO4(s) produced. [Show all work.
Indicate the correct answer in proper significant figures.]
40. The table below shows the data collected during the heating of a 10.0-gram sample of a hydrated salt.
a What is the percent by mass of water in the original sample?
b Why is it important in this experiment to heat the salt until the mass of salt remains constant?
Reference Tables
Answer Key
1. Acceptable responses: A compound must contain two or more
different elements, only 1 kind of atom present.
25. Acceptable responses: 4 H and 2 O on both sides; 4 H = 4 H
and 2 O = 2 O; same number of each element on both sides.
2. Allow credit for 2.
26. 4
3. Allow credit for 3.
27. 0.0010 g
4. 1 Fe2O3 + 3 CO - 2 Fe + 3 CO2
5. a) 23.0 + 35.5 = 58.5 g
mole
6. a) NaCl
b) 1.84 g × 1.00 mole/58.5 g = 0.0315
b) 57.5 grams c) 0.042
7. _1_Ca(ClO3)2 → _1_CaCl2 + _3_O2
8. a) 14.0 + 4(1.0) + 14.0 + 3(16.0) = 80.0 g b) 7.89g × 1.00
mole/80.0g = 0.0986 mole
28. a) 39.1 + 35.5 + 3(16.0) = 122.6 g
mole/122.6g = .373 mole
b) 45.7g x 1.00
29. _6_Li + _1_N2 → _2_Li3N
30. a) 186 grams b) .095 moles c) C2H5O4
31. 11 g × 14444mole
gg or
11
44
32. a) 40.1 + 2(35.5) = 101 grams b) 45.5g x 1.00 mole/101g =
.450 mole
9. 16 or 16.0
33. a) 200.6 + 79.9 = 280.5g
0.352 mole
10. Acceptable responses:
mole 8.4
8.4
8.40g × 158.3
58.3 gg ; 58.3
b) 98.7g × 1.00 mole/280.5g =
34. 4,1,3,2,5
11. 0.025
35. a) 39.1 + 126.9 = 166 grams
.0281 mole
12. NaHCO3
13. 96
36. a) 14.0 + 4(1.0) + 35.5 = 53.5 g
mole/53.5g = .00695 mole
b) 4.66g x 1.00 mole/166g =
b) 0.372g x 1.00
14. Allow credit for C5H12(g) + 8 O2(g) → 5 CO2(g) + 6 H2O(g).
Allow credit even if the coefficient “1” is written in front of C5H1237. _1_Al2(SO4)3 + _3_Ca(OH)2 → _2_Al(OH)3 + _3_CaSO4
(g)
38. _1_Al2(SO4)3 + _3_ZnCl2 → _2_AlCl3 + _3_ZnSO4
15. Allow credit for a numerical setup consistent with the student’s
response to previous question
39. a) 40.1 + 32.1 + 4(16.0) = 136.2 g b) 31.9g x 1.00
mole/136.2g = 0.234 mole
16. 2 H2(l) + O2(l) → 2 H2O(g) + energy
40. a) 20.% b) To insure that all of the water has been driven out
of the salt.
17. a) 39.1 + 14.0 + 3(16.0) = 101 grams
b) 19.8g x 1.00
mole/101g = .196 mole
18. a) 36/ (137 + 71 + 36) × 100 = 15% b) 207 grams
19. Allow credit for a response consistent with the student’s setup and
consistent with the student’s response to previous question.
Significant figures do not need to be used.
20. Acceptable responses: 172, 172.2.
21. _1_Fe2O3(s) + _3_CO(g) → _2_Fe(l) + _3_CO2(g)
22. a) 3 b) 1:2 c) 7.5 moles
d) Exothermic because it releases heat.
23. _2_Al(OH)3 + _3_H2SO4 → _1_Al2(SO4)3 + _6_H2O
24. Acceptable responses: decomposition; analysis; redox;
endothermic; electrolysis.