SCH 3UI – Chapter 5 (Stoichiometry) Review Answer Sheet
KNOWLEDGE AND UNDERSTANDING
A.
Completion. Complete each sentence or statement.
1.
A(n) __excess_____________ reagent is the only reagent left over when all other
reagents have been consumed in a chemical reaction.
2.
A(n) __limiting____________ is a reagent that is completely consumed in a reaction
and thereby limits the amount of product(s) that is/are formed.
3.
When a balanced chemical equation is used to calculate the maximum amount of
product that should form during a reaction, the value obtained is called the
__theoretical yield____.
4.
Once a chemical reaction is actually carried out, the ratio of the actual yield to the
theoretical yield is known as the ___actual yield_______.
5.
__stoichiometry____ is the calculation of the quantities of reactants and products
involved in a chemical reaction.
B.
True/False. Indicate whether the sentence or statement is true or false. Change the
bolded word to correct the statement.
__T__ 1.
Mole ratios that relate reactants to products can be constructed from the coefficients in a
balanced chemical equation.
__F__ 2.
The amount of excess reagent limiting reagent dictates the amount of product formed in a
chemical reaction.
__T__ 3.
In a chemical reaction that involves two reactants, the limiting reagent is identified as the
reactant that is entirely consumed.
__T__ 4.
The percentage yield is the actual amount of a product expressed as a percentage of the
calculated theoretical yield of that product.
__T__ 5.
If 165.0 g of silver iodide was produced in a reaction for which the theoretical yield was
192.0 g, the percentage yield is 85.94%.
__T__ 6.
Producing sodium carbonate using the Leblanc process was proven to be very expensive,
inefficient, and harmful to the environment.
C. Multiple Choice. Identify the letter of the choice that best completes the statement or
answers the question.
__e__ 7.
Which of the following statements is true if 10.0 g of substance A reacts with 15.0 g of substance B?
a. Substance A is the limiting reagent.
b. Substance B is the limiting reagent.
c. Substance A is the excess reagent.
d. Substance B is the excess reagent.
e. not enough information
__c__ 8.
Stoichiometry is defined as:
a. mass and volume relationships in physical changes
b. the relationship between the number of moles of a substance and the mass of the same substance
c. mass and volume relationships in chemical changes
d. the formation of a polymer from monomers
e. the concept that energy is transferred in discrete units
__c__ 9.
Ethane burns in oxygen to produce carbon dioxide and water. The balanced chemical equation is
2C2H6 + 7O2
4CO2 + 6H2O. The molar ratio between the ethane and water is:
b.
2:7
c.
1:3
d.
7:4
e.
4:7
a. 1:2
__a__ 10.
a. 51.9 g
Determine the number of grams of HCl needed to react completely with 12.8 g of aluminum,
according to the following equation: 2Al + 6HCl
2AlCl3 + 3H2
b.
17.3 g
c.
34.6 g
d.
103.8 g
e.
38.4 g
12.8g Al
__d__ 11.
a. 37.6 g
1 mol Al
26.98g Al
a. 1.24 mol
a. 1.5 mol
4.0 mol O2
__a__ 14.
a. zinc
b. sulphur
c. zinc sulfide
8.00g Zn
__a__ 15.
51.9g HCl
1 mol C3H6
42.09g C3H6
6 mol CO2
2 mol C3H6
44.01g CO2
1 mol CO2
151g CO2
Determine the number of moles of silver that are produced when 210 g of silver nitrate are
completely reacted as shown in the following reaction: Sn + 2 AgNO3
2 Ag + Sn(NO3)2
b.
1.78 mol
c.
2.48 mol
d.
3.11 mol
e.
4.07 mol
210g AgNO3
__c__ 13.
36.45g HCl
1 mol HCl
Determine the number of grams of CO2 that can be produced from 48.0 g of the hydrocarbon C3H6,
according to the following equation: 2C3H6 + 9O2
6CO2 + 6H2O
b.
50.2 g
c.
87.8 g
d.
151 g
e.
188.4 g
48.0g C3H6
__a__ 12.
6 mol HCl
2 mol Al
1 mol AgNO3
169.88g AgNO3
2 mol Ag
2 mol AgNO3
1.24 mol Ag
Determine the number of moles of water produced if 4.0 mol of O2 are completely reacted
according to the following balanced equation: 2C3H6 + 9O2
6CO2 + 6H2O
b.
1.9 mol
c.
2.7 mol
d.
4.8 mol
e.
6.0 mol
6 mol H2O
9 mol O2
2.7 mol H2O
Zinc and sulphur react to form zinc sulfide, as shown in the following balanced chemical equation:
Zn + S
ZnS. If 8.00 g of zinc and 8.00 g of sulphur are available for this reaction, the limiting
reagent will be:
d. both zinc and sulphur
e. cannot be determined
1 mol Zn
65.38g Zn
0.122 mol Zn
8.00g S
1 mol S
32.00g S
0.250 mol S
excess
When calcium is allowed to react with nitrogen, N2, calcium nitride is formed, as shown in the
following balanced chemical equation: 3Ca + N2
Ca3N2. If 24.0 g of calcium and 12.0 g of
nitrogen are available for this reaction, the limiting reagent will be:
a. calcium
d. both calcium and nitrogen will be consumed completely
b. nitrogen
e. cannot be determined
c. calcium nitride
24.0g Ca
1 mol Ca
40.08g Ca
0.599 mol Ca
limiting
12.0g N2
1 mol N2
28.02g N2
0.428 mol N2 x 3 = 1.28 mol Ca needed
__c__ 16.
If 2.0 mol of aluminum are allowed to react with 2.8 mol of bromine, determine which of the
statements below is true, given the following balanced equation: 2Al + 3Br2
2AlBr3
a. The aluminum will react completely
d. The aluminum is the limiting reagent
b. The bromine is the reagent in excess
e. Both (a) and (d) are true
c. The bromine is the limiting reagent
2.0 mol Al requires 3.0 mol of bromine
__b__ 17.
a. 71.5%
If 226.1 g of tin(II) chloride was the actual amount obtained in a reaction for which the theoretical
yield was 288.0 g, the percentage yield is:
b.
78.51%
c.
81.98%
d.
84.11%
e.
86.77%
226.1g/288.0g x 100% = 78.51%
__d__ 18.
The LeBlanc process was one method used to produce sodium carbonate in industry. One of the
negative aspects of producing sodium carbonate (soda ash) using this method is:
a. the process was expensive
d. both (a) and (b)
b. the process was environmentally harmful
e. none of the above
c. workers in the industry developed cancer
INQUIRY AND COMMUNICATION
D.
1.
Problem Solving.
Consider the following balanced equation: Mg(OH)2 + 2HCl
MgCl2 + 2H2O
Determine the mass of magnesium chloride produced when 5.91g of Mg(OH)2 is combined with excess HCl.
5.91g Mg(OH)2
2.
1 mol Mg(OH)2
58.33g Mg(OH)2
1 mol MgCl2
1 mol Mg(OH)2
95.21g MgCl2
1 mol MgCl2
Consider the following reaction: Pb(NO3)2 + 2 KI → 2 KNO3 + PbI2
a)
Determine the limiting reactant if 8.30 g of lead (II) nitrate and 7.50 g of potassium iodide are available
for reaction.
b)
How much lead (II) iodide precipitate will be formed given the amounts of reagents above?
8.30g Pb(NO3)2
1 mol Pb(NO3)2
0.0251 mol Pb(NO3)2
x 2 = 0.0502 mol KI needed
7.50g KI
331.22 Pb(NO3)2
8.30g Pb(NO3)2
3.
9.65g MgCl2
1 mol KI
0.0452 mol KI
limiting
166.00g KI
1 mol Pb(NO3)2
331.22g Pb(NO3)2
1 mol PbI2
1 mol Pb(NO3)2
461.00g PbI2
1 mol PbI2
11.6g PbI2
Sodium chloride is produced when sodium metal combines with excess chlorine gas as shown in the following
unbalanced equation: 2 Na + Cl2
2 NaCl. In an experiment, 36.9 g of sodium chloride is produced when
15.9 g of Na and 27.4 g of chlorine are combined. Determine the percentage yield of the product.
15.9g Na
15.9g Na
percentage yield =
1 mol Na
22.99g Na
0.691 mol Na
limiting
1 mol Na
22.99g Na
27.4g Cl2
1 mol Cl2
70.90g Cl2
1 mol NaCl
1 mol Na
actual yield
x 100% = 36.9g Na x 100% = 91.3%
theoretical yield
40.4g Na
0.386 mol Cl2
x 2 = 0.772 mol Na needed
58.44g PbI2
1 mol NaCl
40.4g NaCl
theoretical yield
MAKING CONNECTIONS
E.
Industrial Chemistry
Complete the chart in order to compare the LeBlanc and Solvay Processes.
LeBlanc
Solvay
by-products
CaS (calcium sulfide)
CaCl2 (calcium chloride)
HCl (gas)
energy use
very high – coal was burned to
much lower and more efficient
produce heat to drive many of the most reactions were aqueous
non-aqueous reactions forward
which requires less energy
pollution
HCl gas released in 2 steps
Only by-product was CaCl2 which
(waste products)
coal burned created air pollution could be sold as a de-icing salt
CaS has no uses and was waste
1.
2. The Ostwald process is used to produce nitric acid which has many uses including the production of fertilizers,
pharmaceuticals and explosives. The Ostwald process involves 4 steps – the balanced equations are listed below:
(i)
(ii)
(iii)
(iv)
a)

b)

c)

d)

e)
4 NH3 (gas) + 5O2 (gas) → 4 NO (gas) + 6 H2O (gas)
2 NO (gas) + O2 (gas) → 2NO2 (gas)
3 NO2 (gas) + H2O (liquid) → 2 HNO3 (aq) + NO (gas)
4 NO2 (gas) + O2 (gas) + 2H2O (liquid) → 4HNO3 (aq)
List the intermediate products that are used up in follow steps.
2 NO (gas), 2NO2 (gas), H2O
What is the primary product?
HNO3 (aq)
What are the raw materials?
NH3 (gas), O2 (gas)
What are the by-product(s)?
none
stumper – How many moles of nitric acid are produced from 4 moles of ammonia?