CHEMISTRY 150
December 11th, 2012
Dr. B. MacLean
NAME: (please print) _____________________________
ID #:
____________________________
This is a two-and-a-half (2.5) hour exam.
Read over the entire exam before beginning, and begin by doing those questions which you find easiest. It’s
recommended that you don’t spend more than 30 minutes on the multiple choice questions unless you have time
left over. Try to budget your time according to the value of each question.
There should be 15 pages in this exam (including this page). If your exam copy does not have 15 pages, notify me
immediately.
Necessary data, including equations, constants, an electronegativity table, and a Periodic Table may be found at
the end of the exam questions.
Answer all parts of this exam as indicated. For multiple choice questions, use the data card provided and hand this
card in with your exam when you are finished. Be sure to indicate your name and ID number on this card and the
exam. It is your responsibility to ensure that all of your answers are legible.
READ ALL QUESTIONS CAREFULLY
Questions
Out of
Sec A
30
B1
12
B2
10
B3
14
B4
12
B5
12
B6
10
TOTAL ____________
1
100
Section A; Multiple choice: 30 points (1 each): Answer each of the following multiple choice questions
on the computer card provided by shading (be sure this is dark enough) the letter (A, B, C, or D) that
corresponds to the best response in each case.
A1) Four acids are shown below, along with corresponding pKa values. Which acid is the strongest?
a)
b)
c)
d)
Acid 1, pKa = 6
Acid 2, pKa = 3
Acid 3, pKa = 10
Acid 4, pKa = 5.5
A2) How many millimeters are there in one kilometer?
a)
b)
c)
d)
one million
one thousand
one hundred
10-3
A3) For the following calculation
how many significant figures are there in the answer?
a)
b)
c)
d)
2
3
4
5
A4) Which of the following figures is an exact quantity?
a)
b)
c)
d)
the number of ounces in a pound
the number of centimeters in a yard
the number of dm3 in a quart
the number of gallons in a liter
A5) In 6.0g of water, there will be approximately _______ hydrogen atoms
a)
b)
c)
d)
2.0 x 1023
6.0 x 1023
4.0 x 1023
3.0 x 1023
A6) How many orbitals are in the second energy shell?
a)
b)
c)
d)
2
4
6
8
2
A7) A cylinder with a volume of 10.0 L contains a mixture of 2.00 mole O2 gas and 8.00 moles of N2 gas
25oC. The volume of the O2 gas is _____ L.
a)
b)
c)
d)
10.0 L
2.00 L
22.4 L
24.6 L
A8) Which one of the following is always a characteristic of a chemical change?
a) heat is absorbed
b) a change of state occurs
c) light is emitted
d) one (or more) new substance is formed
A9) Which of the following reactions must be exothermic?
a)
b)
c)
d)
an exchange reaction
a single replacement reaction
a decomposition reaction
a combustion reaction
A10) According to VSEPR theory, the molecular geometry for the nitrate ion is
a)
b)
c)
d)
linear
trigonal planar
trigonal pyramid
tetrahedral
A11) The kinds of intermolecular forces that are responsible for a salt (e.g. NaCl) dissociating in water
are known as
a)
b)
c)
d)
London forces
H-bonding
dipole-dipole forces
ion-dipole forces
A12) The following data describes activation energy (Ea) and reactant-product energy difference (E)
data for four reactions. What data set describes the fastest reaction? (J = joule, a unit of energy)
a)
b)
c)
d)
Ea = 10 J; E = 500 J
Ea = 1000 J; E = -200 J
Ea = 100 J; E = 50 J
Ea = 100 J; E = -500 J
3
A13) Which of the following molecular compounds would you expect to be water-soluble?
a)
b)
c)
d)
CF4
NH3
CO2
F2
A14) Which of the following molecules can form hydrogen bonds with other molecules like itself?
a)
b)
c)
d)
CH4
CH3F
CH3CN
CH3COOH
b
a
c
d
A15) When NaCl is added to pure water
a)
b)
c)
d)
the vapor pressure of the resulting solution will be lower than for pure water
the boiling point of the resulting solution is lower than for pure water
the resulting solution will have a higher freezing point than pure water
the resulting solution will be volatile
A16) If red blood cell fluid has an osmolarity of 0.30 M, which of the following solutions would cause the
red blood cells to shrivel up when added to blood?
a)
b)
c)
d)
0.10 M Na2SO4
0.30 M C6H12O6
0.12 M NaCl
0.08 M Na3PO4
4
A17) The mass of an apple was measured using two different balances (weighed five times by each
balance) yielding the following masses, in grams:
Balance 1) 55.3, 55.9, 56.0, 55.7, 55.2
Balance 2) 55.5, 55.7, 55.6, 55.4, 55.5
If the true mass of the apple is 55.6 g, which of the following statements is true?
a)
b)
c)
d)
the data for balance 1 is more accurate and more precise than the data for balance 2
the data for balance 1 is less accurate and less precise than the data for balance 2
the data for balance 1 is more accurate and less precise than the data for balance 2
the data for balance 1 is less accurate and more precise than the data for balance 2
A18) Earlier this year (2012), I carried out a demonstration that involved heating/cooling a glow stick.
What topic in the course did this experiment describe?
a)
b)
c)
d)
solubility
buffers
pressure
reaction rates
A19) In order to increase the solubility of CO2 in soda pop, the partial pressure of CO2 above the solution
is increased just before bottling. The increased solubility of CO2 is described by
a)
b)
c)
d)
Henry’s law
Dalton’s law
Boyle’s law
Charles’s law
A20) Which of the following acids is a strong acid?
a)
b)
c)
d)
HF
HNO3
H2S
HClO
A21) Which of the following ions is not a weak base in water?
a)
b)
c)
d)
BrCNFS2-
5
A22) Which of the following species has the lowest mass?
a)
b)
c)
d)
a H+ ion
a neutron
a proton
an electron
A23) An isotope of potassium has two more neutrons than protons. Its chemical symbol would be
a)
b)
c)
d)
A24) Pressure is defined as
a)
b)
c)
d)
volume divided by temperature
force divided by area
mass times acceleration
volume divided by area
A25) A covalent bond is
a)
b)
c)
d)
an intramolecular force
an instantaneous dipole-dipole interaction
an attraction that exists between oppositely charged ions
an intermolecular force
A26) Which of the following processes describes the transformation of matter from the solid state to a
gas?
a)
b)
c)
d)
condensation
evaporation
melting
sublimation
A27) Which of these elements is found as a diatomic molecule in its elemental form?
a)
b)
c)
d)
helium
bromine
boron
carbon
6
A28) Which of the following molecules is linear?
a)
b)
c)
d)
PH3
CS2
SF2
O3
A29) Which of these compounds possesses one or more coordinative covalent bonds?
a)
b)
c)
d)
H2S
PCl3
CO2
SO2
A30) Which of the following salts should produce a basic solution when dissolved in water?
a)
b)
c)
d)
Ca(C2H3O2)2
NaNO3
KBr
NH4Cl
(salts section – not covered)
7
Section B; Problems: 70 points (6 questions): Answer each of the following questions in the space
provided.
B1) The pH of gastric acid is 2.5. What is [H3O+] in gastric acid? [2]
10  pH  [ H 3O  ]
10 2.5  [ H 3O  ]  3.16 x10 3 M
b) What is [OH-] in a solution that has a pH = 12.5? (assume T = 25oC) [3]
10  pH  [ H 3O  ]
10 12.5  [ H 3O  ]  3.16 x10 13 M
[ H 3O  ][OH  ]  K w
[OH  ] 
Kw
1x10 14

 3.16 x10 2 M
[ H 3O  ] [3.16 x10 13 ]
c) A 0.025 M solution of the weak acid, HX, is found to be 8.5% ionized at 25oC.
i) Write the equation describing how HX ionizes in water [1]
HX(aq) + H2O(l)  H3O+(aq) + X-(aq)
ii) Calculate Ka for this acid. [4]
What is 8.5% of 0.025M? (0.085)(0.025M) = 0.002125M. This is the amount that ionizes. The amount
that ionizes is the amount of H3O+ and X- produced at equilibrium. The amount of HX left at equilibrium
is 0.025M – 0.002125M = 0.022875M. This is [HX] at equilibrium. Ka is thus:
Ka 
[ H 3O  ][ X  ] [0.002125][0.002125]

 1.97404...x104  2.0 x10 4
[ HX ]
[0.022875]
iii) Calculate the pH of this solution [2]
[H3O+] at equilibrium was 0.002125M, so pH = -log[H3O+] = -log[0.002125] = 2.67 (2 decimals because
this number is 8.5% of 0.025M).
8
B2a) A blood concentration of 0.065 M ethyl alcohol (CH3CH2OH) is sufficient to induce a coma. At this
concentration what is the total mass of ethyl alcohol in an adult male whose blood volume is 5.6L? [4]
M
mol
V ( L)
mol _ ethanol
5.6 L
0.065M 5.6 L   0.364mol _ ethanol
0.065M 
Molar mass of CH3CH2OH: 2C + 6H + O 1 mol = 46.08g, so
 46.08 g 
  16.77312 _ g _ ethanol  16.8 g _ ethanol
0.364mol
 1 _ mol 
b) If a glucose (C6H12O6) solution has a concentration of 2.75% (m/v), what is the molarity of this
solution? [3]
molar mass of glucose = 6C + 12H + 6O  1 mol C6H12O6: 180.18 g C6H12O6
For 100 mL of this solution, there would be 2.75g of C6H12O6. Knowing the molar mass, we can compute
the mol of C6H12O6. Knowing the volume of the solution in L, we can get molarity:
 1 _ mol _ C6 H12O6 
  0.0152625...mol _ C6 H12O6
2.75 g _ C6 H12O6 
 180.18 _ g _ C6 H12O6 
mol 0.0152625...mol _ C6 H12O6
M

 0.153M _ C6 H12O6
V ( L)
0.100 _ L
c) What is the % (m/v) concentration of a 3.5 M NaCl solution? [3]
For a 3.5 M solution, there are 3.5 mol of NaCl in 1L of solution. The molar mass of NaCl is 58.44 g, so:
M
mol
V ( L)
 58.44 g _ NaCl 
  204.54 g _ NaCl
3.5mol _ NaCl 
 1 _ mol _ NaCl 
This is 204.54g NaCl in 1L (1000 mL) of solution. The %(m/v) concentration would then be:
 204.54 g _ NaCl 
  100%  20.454%  20.%
%(m / v)  
 1000 _ mL _ solution 
9
B3a) In the CHEM 150 lab this semester, the following reaction was carried out:
Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g)
The reaction was conducted in an upside-down tube and the H2(g) generated was collected over water.
Using the following data, calculate the moles of H2(g) made by this reaction. [5]
temperature: 22 oC
volume of H2(g) collected: 22.50 mL
room pressure: 754 mm Hg
PH2O at 22oC: 19.8 mm Hg
You need to use PV = nRT to solve for the mol H2 produced. You also need to ensure that you are not
including the pressure created by H2O vapor in the container. You do this by subtracting 19.8 mm Hg
from 754 mm Hg:
754 mm Hg – 19.8 mm Hg = 734.2 mm Hg (this is the pressure of H2 alone).
PV  nRT
PV 734.2mm _ Hg )(0.02250 L 
n

 8.97 x10 4 mol _ H 2
L
*
mm
_
Hg
RT 

 62.4
295K 
mol * K 

b) A sample of CO gas has a volume of 7.31 L at a pressure of 735 mm Hg and a temperature of 45oC.
What is the temperature of this gas (oC) when the pressure is 1275 mm Hg and the volume is 0.800 L?
[3]
P1V1 P2V2
PV T

 T2  2 2 1
T1
T2
P1V1
T2 
1275mm _ Hg 0.800 L 318K   60.37019...K
735mm _ Hg 7.31L 
60.37019K = T(oC) + 273  T(oC) = -213oC
c) Answer each of the following questions in the space provided. [6]
What type of energy is related to disruptive forces? _kinetic energy_.
How do molecules transfer energy to each other? _through collisions_.
Matter is anything that _takes up space_ and possesses _mass_.
10
B4a) When 12.03g of methane (CH4) is combusted, 14.87 g of H2O is obtained. What is the % yield for
this reaction? [6]
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
 1mol _ CH 4  2mol _ H 2O  18.02 g _ H 2O 


  27.01315 g _ H 2O
12.03g _ CH 4 
16
.
05
g
_
CH
1
mol
_
CH
1
mol
_
H
O
4 
4 
2


To calculate % yield (not covered this year) you take the amount of H2O actually produced and divide by
the amount of H2O that can (theoretically) be made from 12.03g CH4:
 actual _ amount _ of _ H 2O 
 14.87 g _ H 2O 
  100%  
  100%  55.05%
% yield  
theoretica
l
_
amount
_
of
_
H
O
27
.
01315
g
_
H
O
2
2




b) A solution is made by dissolving NH3 and NH4Cl into water. A solution of HNO3 is then added.
Write the equation for the chemical reaction that occurs when the HNO3 solution is added. [3]
buffers
c)
Would you expect the pH of the solution to be lower or higher after the addition of the HNO3
solution? [1]
buffers
Answer: ________________________________
d)
What is the function of a buffer? [2]
buffers
11
B5a) Silver has only two isotopes. The first isotope has an abundance of 51.82% and a mass of 106.9
amu. The second has a mass of 108.9 amu. Calculate the atomic mass of silver. [3]
Atomic mass = (0.5182)(106.9 amu) + (0.4818)(108.9 amu) = 107.86 amu
b) For the reaction shown below, indicate the oxidizing agent: [2]
Answer = _S_
4H2O + 3S + 2NO  2HNO3 + 3H2S
c) For the exothermic chemical reaction shown below, indicate whether the following changes made to
a mixture of products and reactants at equilibrium results in an increase/decrease/no effect in the
yield of NO: [5]
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g)
a)
increase the temperature
_decrease yield of NO_
b)
addition of NH3(g)
_increase yield of NO_
c)
removal of O2(g)
_decrease yield of NO_
d)
increase the container volume
_increase yield of NO_
e)
increase of total pressure by adding neon
_____no effect______
d) Write an expression for the equilibrium constant, Keq, for this reaction: [2]
K eq 
[ NO]4 [ H 2O]6
[ NH 3 ]4 [O2 ]5
12
B6) Answer the following questions:
a) Write the equations that describe how the diprotic acid, H2CO3, ionizes when put into water. [4]
H2CO3(aq) + H2O(l)  HCO3-(aq) + H3O+(aq)
HCO3-(aq) + H2O(l)  CO32-(aq) + H3O+(aq)
b) Indicate the full electron configuration for bromide ion, Br- (no noble gas shortcut) [2]
Br-: 1s22s22p63s23p64s23d104p6
c) Write the balanced chemical equation for the neutralization reaction that occurs when H2SO4
reacts completely with LiOH. [2]
H2SO4 + 2LiOH  Li2SO4 + 2H2O
d) Does the solution in part “c” that is created by the neutralization reaction have an acidic, basic,
or neutral pH? [2]
Answer = _neutral_(salts)______
HOORAY!!!!! Bonus questions!!!!!!!!!!!!!
Name one useful thing you’ve learned in this course so far: [1] __________________________________
_____________________________________________________________________________________
In the liquid nitrogen demonstration this year, what was the balloon’s name? [1] ___________________
ENJOY YOUR HOLIDAYS!!!!!!!
13
Formulas, constants
M 
given _ units  desired _ units   desired _ units
 actual _ yield
% yield  
 theoretica l _ yield
pH   log[ H 3O  ]
 mass _ of _ solute 
 *100%
%(m / m)  
 mass _ of _ solution 
 volume _ of _ solute 
 *100%
%(v / v)  
 volume _ of _ solution 
moles _ of _ solute
L _ of _ solution
C1V1  C2V2
10  pH  [ H 3O  ]
pH  pK a  log
pK a   log K a 

[A ]
[ HA]
[ H 3O  ][OH  ]  K w  1x10 14
pH  pOH  14.00
PV  nRT
 given _ units 

100%

 grams _ of _ solute 
 *100%
%(m / v)  
 mL _ of _ solution 
osmolarity  M * i
[C ] y [ D] z
K eq 
[ A]w [ B ] x
wA  xB  yC  zD
atomic _ mass  % _ abund _ X mass _ X   ...
L. atm
mol . K
1atm  760torr  760mmHg
V1 V2

T 1 T2
R  0.0821
P1V1  P2V2
P1V1 P2V2

T1
T2
PTot  PA  PB  PC ...
T ( K )  T ( o C )  273
14
15