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Question
The formula mass (FM) of barium phosphite,
Ba3(PO3)2 is
a)
b)
c)
d)
e)
184.30 amu.
216.30 amu.
295.27 amu.
190.37 amu.
569.93 amu.
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3|1
Answer
e) 569.93 amu.
The formula mass of a substance is the sum of the
atomic weights of all of the atoms in the compound. Be
careful to use all of the subscripts when counting the
atoms in Ba3(PO3)2.
Ba: 3 × 137.33 amu = 411.99 amu
P:
2 × 30.97 amu = 61.94 amu
O: 2 × 3 × 16.00 amu = 96.00 amu
569.93 amu
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3|2
Question
You have a sample of zinc (Zn) and a sample of
aluminum (Al). You have an equal number of atoms in
each sample. Which of the following statements
concerning the masses of the samples is true?
a) The mass of the zinc sample is more than twice as great
as the mass of the aluminum sample.
b) The mass of the zinc sample is more than the mass of the
aluminum sample, but it is not twice as great.
c) The mass of the aluminum sample is more than twice as
great as the mass of the zinc sample.
d) The mass of the aluminum sample is more than the mass
of the zinc sample, but it is not twice as great.
e) The masses of each sample are equal.
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3|3
Answer
a) The mass of the zinc sample is more than
twice as great as the mass of the
aluminum sample.
Since zinc has an atomic mass more than twice
that of aluminum, the sample of zinc with the
same number of atoms will have more than
twice the mass of the sample of aluminum.
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3|4
Question
Which of the following is the most accurate
description of a mole?
a) The mass of carbon in a measured sample of
carbon
b) The number of atoms in any given mass of an
element
c) The number of sodium ions in 58.44 g of
sodium chloride
d) At least two of the above are accurate
descriptions of a mole.
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3|5
Answer
c) The number of sodium ions in 58.44 g of
sodium chloride
The molar mass of sodium chloride (NaCl) is
58.44 g. Since there is 1 atom of sodium for
each unit of sodium chloride, 58.44 g of NaCl
will contain 1 mol of sodium ions.
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3|6
Question
Which of the following is closest to the
average mass of one atom of copper?
a)
b)
c)
d)
e)
63.55 g
52.00 g
58.93 g
65.38 g
1.055 × 10−22 g
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3|7
Answer
e) 1.055 × 10−22 g
1 atom Cu
1 mole Cu
63.55 g Cu
6.022 x 1023 atomc Cu
1 mole Cu
= 1.055 × 10−22 g
Also, one atom must have a very low mass, and
choice e) is the only choice with the correct
order or magnitude.
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3|8
Question
Which of the following 100.0-g samples
contains the greatest number of atoms?
a)
b)
c)
d)
e)
Magnesium
Zinc
Silver
Calcium
All samples contains the same number
of atoms.
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3|9
Answer
a) Magnesium
Divide 100.0 g by each of the atomic masses.
Or, since Mg has the lowest atomic mass, the
number of atoms must be the greatest.
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3 | 10
Question
For which of the following compounds does 1.0 g
represent 2.27  10−2 mol?
a)
b)
c)
d)
H2O
CO2
NH3
C2H6
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Answer
b)
CO2
The answer may be obtained by solving for
molar mass: (1.0 g)(1 mol/molar mass) =
2.27  10−2 mol. The molar mass obtained
(44 g/mol) is closest to the answer CO2.
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3 | 12
Question
The mass of 0.822 mol of a diatomic molecule
is 131.3 g. Identify the molecule.
a)
b)
c)
d)
F2
Cl2
Br2
I2
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3 | 13
Answer
c)
Br2
The answer may be obtained by solving for
molar mass: (131.3 g)(1 mol/molar mass) =
0.822 mol. The molar mass obtained
(160. g/mol) is closest to the answer Br2
(2 × 79.90 g/mol).
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3 | 14
Question
Which of the following 100.0-g samples
contains the greatest number of oxygen
atoms?
a)
b)
c)
d)
e)
H2O
N2O
C3H6O2
CO2
All of the sample have the same number
of oxygen atoms.
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3 | 15
Answer
a) H2O
Divide 100.0 g by the molar mass of each compound
and multiply by the number of oxygen atoms in the
formula. The greater the number of moles of O atoms,
the greater the number of O atoms.
H2O:
N2O:
1 mol H2O
1 mol O
= 5.551 mol O
(2.016 + 16.00) g H2O 1 mol H2O
1 mol N2O
1 mol O
100.0 g N2O 

= 2.272 mol O
(28.02 + 16.00) g N2O 1 mol N2O
100.0 g H2O 
C3H6O2:
100.0 g C3H6O2 

1 mol C3H6O2
(36.03 + 6.048 + 32.00) g C3H6O2

2 mol O
1 mol C3H6O2
= 2.700 mol O
1 mol CO2
2 mol O
100.0
g
CO


CO2:
2
(12.01 + 32.00) g CO2 1 mol CO2
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= 4.544 mol O
3 | 16
Question
Which of the following 100.0-g samples
contains the highest percentage oxygen
by mass?
a)
b)
c)
d)
e)
H2O
N2O
C3H6O2
CO2
All of the sample have the same number
of oxygen atoms.
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3 | 17
Answer
a) H2O
The mass of the samples does not matter, nor does it
matter that the samples have the same mass.
H2O: [(16.00 g)/(2.016 + 16.00) g] × 100% = 88.81% O
N2O: [(16.00 g)/(28.02 + 16.00) g] × 100% = 36.35% O
C3H6O2: [(32.00 g)/(36.03 + 6.048 + 32.00) g] × 100%
= 43.20% O
CO2: [(32.00 g)/(12.01 + 32.00) g] × 100% = 72.71% O
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3 | 18
Question
In combustion analysis, the mass of oxygen, in a sample
containing only carbon, hydrogen, and oxygen
a) is determined using the mass of carbon dioxide,
CO2, collected in an absorber and converting it to
mass of oxygen.
b) is determined using the mass of water, H2O,
collected in an absorber and converting it to mass of
oxygen.
c) is determined by difference, using the initial sample
weight and subtracting the amounts of carbon and
hydrogen collected by the absorbers.
d) is determined by adding the amounts of oxygen
collected by the carbon dioxide and water
absorbers.
e) cannot be determined in a combustion analysis.
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3 | 19
Answer
c)
is determined by difference, using the initial
sample weight and subtracting the amounts of
carbon and hydrogen collected by the
absorbers.
Since the compound contains only carbon, hydrogen,
and oxygen, we can calculate the mass of oxygen by
difference. The carbon weight in the sample is
calculated using the mass of carbon dioxide, CO2,
collected in an absorber. The hydrogen weight in the
sample is calculated using the mass of water, H2O,
collected in an absorber. So the mass of O =
sample weight − (carbon weight + hydrogen weight)
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Question
The empirical formula of styrene is CH; its
molar mass is 104.1. What is the molecular
formula of styrene?
a)
b)
c)
d)
C2H4
C8H8
C10H10
C6H6
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3 | 21
Answer
b)
C8H8
Since the molecular formula is (CH)n, the n may
be obtained from the equation
(n)(12.0 g/mol + 1.0 g/mol) = 104.1 g/mol,
and so n = 8.
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3 | 22
Question
Which of the following compounds have a
different empirical formula than the other
compounds?
a)
b)
c)
d)
Glucose, C6H12O6
Sucrose, C12H22O11
Fructose, C6H12O6
Ribose, C5H10O5
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3 | 23
Answer
b)
Sucrose, C12H22O11
All simple carbohydrates have a molecular
formula of CnH2nOn, and an empirical formula
CH2O. For glucose n = 6, for fructose n = 6,
and for ribose n = 5. Sucrose is a complex
carbohydrate, with an empirical formula of
C12H22O11.
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3 | 24
Question
In the reaction
4NH3 (g) + 5O2 (g)  4NO (g) + 6H2O (g)
How many grams of H2O are generated when
1.54 moles of NH3 react ?
a)
b)
c)
d)
e)
2.31 g H2O
41.6 g H2O
18.5 g H2O
39.3 g H2O
6.51 g H2O
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3 | 25
Answer
b) 41.6 g H2O
Using the balanced chemical equation, 4 mol of
NH3 would generate 6 mol of H2O, so
1.54 mol NH3 
6 mol H2O
4 mol NH3
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18.02 g H2O

= 41.6 g H2O
1 mol H2O
3 | 26
Question
In the reaction 2A + 3B  C
4.0 moles of A react with 4.0 moles of B.
Which of the following choices best answers the
question: “Which reactant is limiting?”
a) Neither is limiting because equal amounts
(4.0 mol) of each reactant are used.
b) A is limiting because two is smaller than three (the
coefficients in the balanced equation).
c) A is limiting because there are 2 moles but 4.0
moles are needed.
d) B is limiting because three is larger than two (the
coefficients in the balanced equation).
e) B is limiting because there are 4.0 moles but 6.0
moles are needed.
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Answer
e)
B is limiting because there are 4.0 moles
but 6.0 moles are needed.
Using the balanced chemical equation, 4.0 mol
of A would require (4.0 mol A)(3 mol B/2 mol A)
or 6.0 mol of B, but there are only 4.0 mol of B,
so B is the limiting reactant.
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3 | 28
Question
The limiting reactant in a reaction
a) has the lowest coefficient in a balanced
equation.
b) is the reactant for which you have the fewest
number of moles.
c) has the lowest ratio of moles
available/coefficient in the balanced equation.
d) has the lowest ratio of coefficient in the
balanced equation/moles available.
e) none of these
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3 | 29
Answer
c) has the lowest ratio of moles
available/coefficient in the balanced
equation.
Using the moles of materials available and the
balanced chemical equation, the ratio of the
moles of a material available to its
corresponding coefficient in the balanced
equation gives the quantity available per
quantity needed. By comparing these ratios, the
smallest will be the limiting reactant.
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3 | 30
Question
Consider the following balanced equation:
A + 5B  3C + 4D
Which of the following choices best answers the
question, When equal masses of A and B are reacted,
which is limiting?
a) If the molar mass of A is greater than the molar
mass of B, then A must be limiting.
b) If the molar mass of A is less than the molar mass of
B, then A must be limiting.
c) If the molar mass of A is greater than the molar
mass of B, then B must be limiting.
d) If the molar mass of A is less than the molar mass of
B, then B must be limiting.
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3 | 31
Answer
d) If the molar mass of A is less than the molar
mass of B, then B must be limiting.
Since the masses are equal, if the molar mass
of A is less than that of B, the number if moles
of A will be greater than the number of moles of
B. Since more moles of B are required (a 1:5
ratio of A:B according to the balanced
equation), B must be limiting.
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3 | 32
Question
Which of the following reaction mixtures would
produce the greatest amount of product
according to the following chemical equation?
2H2 + O2  2H2O
a)
b)
c)
d)
e)
2 mol H2 and 2 mol O2
2 mol H2 and 3 mol O2
2 mol H2 and 1 mol O2
3 mol H2 and 1 mol O2
Each of the choices above would produce the
same amount of product.
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3 | 33
Answer
e) Each of the choices above would produce
the same amount of product.
Each will produce 2 mol of H2O:
For choice a, H2 is limiting; 2.0 mol H2 will produce
2.0 mol H2O.
For choice b, H2 is limiting; 2.0 mol H2 will produce
2.0 mol H2O.
For choice c, neither is limiting; 2.0 mol H2 will
produce 2.0 mol H2O; 1.0 mol O2 will
produce 2.0 mol H2O.
For choice d, O2 is limiting; 1.0 mol O2 will produce
2.0 mol H2O.
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3 | 34
Question
Methyl salicylate (oil of wintergreen) can be prepared in
the lab by heating salicylic acid, C7H6O3, with methanol,
CH3OH, according to the following reaction:
C7H6O3 + CH3OH  C8H8O3 + H2O
If the student starts with 2.53 g of salicylic acid and an
excess of methanol and collects 2.62 g of methyl
salicylate, what is the student’s percentage yield?
(Hint: molecular weight [MW] C7H6O3= 138.12 g/mol; MW CH3OH =
32.04 g/mol; MW C8H8O3 = 152.14 g/mol)
a)
b)
c)
d)
94.0%
106%
96.7%
87.7%
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3 | 35
Answer
a) 94.0%
The theoretical yield is
2.53 g C7H6O3 
1 mol C7H6O3
138.12 g C7H6O3

1 mol C8H8O3
1 mol C7H6O3

152.14 g C8H8O3
=
1 mol C8H8O3
= 2.79 g C8H8O3
So the percentage yield is
2.62 g C8H8O3
actual yield
 100% =
100% = 94.0%
theoretical yield
2.79 g C8H8O3
Note that the percentage yield must be less than 100%.
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3 | 36
Question
A student adds 85.92 g of KCl to a 500.00-mL
volumetric flask. He then adds water, dissolves
the solids, and dilutes the flask to the mark.
What is the molar concentration of KCl in the
flask?
a)
b)
c)
d)
172 M KCl
1.72 M KCl
4.610 M KCl
2.305 M KCl
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3 | 37
Answer
d) 2.305 M KCl
Molarity is defined as moles of solute per
liter of solution.
85.92 g KCl 1 mole KCl
500.0 mL 74.55 g KCl
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1000 mL
1L
= 2.305 M
KCl
3 | 38
Question
Consider five solutions that each have the same
mass of solute in 100.0 mL of solution. Which
has the highest concentration as measured in
molarity?
a)
b)
c)
d)
e)
KCl
NaCl
Na2SO4
NaF
CaCl2
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3 | 39
Answer
d)
NaF
The highest concentration as measured in
molarity for the same volume of solution
will be determined by the solute with the
smallest molar mass.
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3 | 40
Question
Which of the following solutions contains
the greatest number of ions?
a)
b)
c)
d)
400.0 mL of 0.10 M NaCl
300.0 mL of 0.10 M CaCl2
200.0 mL of 0.10 M FeCl3
800.0 mL of 0.10 M sucrose
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3 | 41
Answer
b) 300.0 mL of 0.10 M CaCl2
The concentrations are all the same, so we
must look at the volumes and number of ions
per compound. While FeCl3 dissolves into four
ions, and CaCl2 dissolves into only three, the
greater volume of the CaCl2 solution more than
makes up for this.
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3 | 42
Question
Which of the following solutions contains the
greatest total ion concentration?
a) One mole of potassium chloride dissolved in
1.0 L of solution
b) One mole of iron(II) nitrate dissolved in 1.0 L of
solution
c) One mole of potassium hydroxide dissolved in
1.0 L of solution
d) One mole of sodium phosphate dissolved in
1.0 L of solution
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3 | 43
Answer
d) One mole of sodium phosphate dissolved in
1.0 L of solution
All of the possible answers are strong electrolytes, so
the one that dissociates into the most ions (KCl into 2mol ions, Fe(NO3)2 into 3-mol ions, KOH into 2-mol
ions, Na3PO4 into 4-mol ions) is the answer.
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3 | 44
Question
You have separate aqueous solutions of NaOH
and Ca(OH)2 with the same concentrations.
You wish to neutralize an aqueous solution of
HCl. Which basic solution would require more
volume to neutralize the acid?
a) The NaOH solution
b) The Ca(OH)2 solution
c) More information is needed to answer this
question.
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3 | 45
Answer
a)
The NaOH solution
The basic solution requiring the greater
volume to neutralize the acid is the one
with the fewer hydroxide ions available to
react with the hydrogen ions.
2 HCl (aq) + Ca(OH)2 (aq)  CaCl2 (aq) + H2O (l)
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
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3 | 46
Question
A student needs to prepare 250.0 mL of a
0.300 M BaCl2 and has a stock solution of
1.50 M BaCl2. What volume of the
concentrated stock solution does the student
need to prepare the dilute solution?
a)
b)
c)
d)
e)
50.0 mL
1250 mL
250 mL
112.5 mL
200. mL
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3 | 47
Answer
a) 50.0 mL
Because the moles of solute do not change during
dilution, Mi × Vi = Mf × Vf. This equation can be
rearranged to
Vi 

Mf  Vf

Mi
0.300 M BaCl2  250.0 mL
1.50 M BaCl2
= 50.0 mL of 1.50 M BaCl2
the concentration of the dilute solution is one-fifth of the
concentrated solutions, so the volume needed is onefifth of the dilute solution volume.
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3 | 48