Name: ________________________
Student Number: _____________________
Chemistry 2100 Practice Final
INSTRUCTIONS
1) Read the exam carefully before beginning. There are 25 questions on 14 pages followed by a
periodic table and a blank page for any rough work. Please ensure that you have a
complete exam. If not, let Susan or Greg know immediately. All pages must be
submitted at the end of the exam.
2) Write your first and last name on every page of the exam.
3) When drawing structures, show stereochemistry if applicable.
4) Show your work for all calculations. Answers without supporting calculations will not be
given full credit.
5) Marks will be deducted for improper use of significant figures.
6) If your work is not legible, it will be given a mark of zero.
7) In some sections, you are given a choice of questions. If you answer more than the number
of questions required, clearly mark which answers you want marked. If it is not clear, only
the first answers provided will be marked.
8) You may use a calculator.
9) You may use a molecular modeling kit if you brought one with you in a transparent plastic
bag as outlined on the CHEM 2100 website.
10) Do not open the exam until you are told to begin. Beginning prematurely will result in
removal of your exam paper and a mark of 0.
11) You have 3 hours to complete this exam.
Q
1
2
3
4
5
6
7
8
9
10
/7
/4
/3
/9
/4
/4
/3
/ 10
/4
/3
Q
11
12
13
14
15
16
17
18
19
20
/3
/4
/9
/4
/8
/5
/6
/6
/4
/ 10
Q
21
22
23
24
25
Total
/
/
/
/
/
11
7
6
3
8
/ 145
Name: ________________________
Student Number: _____________________
1.
Answer the following questions in the space provided.
[7 marks]
(a)
What are two things that the noble gases all have in common?
They are unreactive (inert).
They all have complete valence shells.
(b)
What group number are the alkaline earth metals in?
2
(c)
Give two examples of halogens.
F, Cl, Br, I, At (any two)
(d)
What trend does electronegativity follow across a period?
It increases from left to right.
(e)
Would you expect the chemical reactions of In to be most similar to those of I, Sn, Al, or
Ir?
Al (both in same group)
(f)
Name two elements in the periodic table that exist as gases at room temperature.
hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine,
argon, krypton, xenon, radon (any two)
2.
Complete the following table.
Symbol
202
+
Hg
80
48
4+
22 Ti
[4 marks]
Atomic
Number
Mass
Number
Number of
Protons
Number of
Neutrons
Number of
Electrons
80
202
80
122
79
22
48
22
26
18
Name: ________________________
3.
Student Number: _____________________
Draw the structure of a molecule that will give a positive Benedict’s test. What features
of this molecule are necessary for the positive test?
[3 marks]
Any aldehyde that has a hydroxy group attached to carbon 2 (the carbon next to the
carbonyl group).
O
e.g.
O 2 C
H
C 1 H
H H
Necessary features: (1) aldehyde, and (2) hydroxy group attached to carbon 2
4.
The following names are incorrect according to IUPAC rules. For each name, draw the
structure and give the correct IUPAC name.
[9 marks]
(a)
4-benzylbutane
1-phenylpentane
(b)
(or pentylbenzene)
2-methyl-1,3,3-triethyl-4-cyclopentene
3,3,5-triethyl-4-methylcyclopentene
(c)
2-methyl-3-isobutyl-6-oxo-4-heptanol
OH
O
4-hydroxy-5-isopropyl-7-methyl-2-octanone
Name: ________________________
Student Number: _____________________
5.
Balance the following reactions:
[4 marks]
(a)
2 KMnO4 + 16 HCl
5 Cl2 + 2 MnCl2 + 2 KCl + 8 H2O
(b)
2 POBr3 + 3 Mg
2 PO + 3 MgBr2
(c)
2 C7H5N3O6
3 N2 + 7 CO + 7 C + 5 H2O
(d)
4 NH3 + 5 O2
4 NO + 6 H2O
6.
Circle and name the most important functional group according to IUPAC rules in
each of the following molecules.
[4 marks]
F
O
O
alkene
H
aldehyde
thiol
O
SH
OH
ketone
7.
Complete the following table. Assume that the atoms are neutral. Do not use noble gas
notation for core electrons.
[3 marks]
Symbol
Electron Configuration
Number of
Valence Electrons
Al
1s22s22p63s23p1
3
Kr
1s22s22p63s23p64s23d104p6
8
Pb
1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2
4
Name: ________________________
8.
(a)
Student Number: _____________________
Ethanol (density = 0.79 g/mL) has been proposed as a clean burning fuel. Write the
balanced chemical equation for the complete combustion of ethanol.
[3 marks]
OH
C2H6O
(b)
+
3 O2
= C2H6O
→
2 CO2 +
3 H2O
If ethanol is combusted with 82.5% yield, what volume of ethanol most be burned to give
2.0 L of water (density = 1.00 g/mL)?
[7 marks]
There are several different ways to work through the logic for this question.
Any route that gets you the correct answer is valid.
1. Using percent yield, find out what the theoretical yield for this reaction would have been.
% yield = actual yield × 100%
theoretical yield
theoretical yield = actual yield × 100%
percent yield
= 2.0 L × 100%
82.5%
theoretical yield = 2.4 L
*** 2 sig. fig.***
2. Convert the theoretical yield to moles.
moles H2O = 2.4 L H2O × 1000 mL × 1.00 g H2O × 1 mole H2O
1L
1 mL H2O
18.015 g H2O
2
moles H2O = 1.3 × 10 moles H2O
***2 sig. fig.***
3. Use the mole ratio to find out how many moles ethanol would need to be burned.
moles C2H6O = 133 moles H2O × 1 mole C2H6O
3 moles H2O
moles C2H6O = 44 moles C2H6O
***2 sig. fig.***
4. Convert the amount of ethanol from moles to volume.
volume C2H6O = 44 moles C2H6O × 46.069 g C2H6O × 1 mL C2H6O
1 mole C2H6O
0.79 g C2H6O
volume C2H6O = 2.5 × 103 ml C2H6O
***2 sig. fig.***
= 2.5 L C2H6O
Name: ________________________
9.
Of the following pairs of molecules, which is more stable? Give one good reason why.
[4 marks]
choice and reason
H
H
A is more stable.
A has no eclipsed hydrogens (unlike B).
vs
Also, B has two “flagpole” hydrogens that
A
B
are very close.
Cl
H
H
H
Cl
H
ClH
Cl
H
A is more stable.
In A, the H and Cl atoms are staggered
(technically, “gauche”).
In B, they are eclipsed.
vs
HH
B
A
10.
Student Number: _____________________
Draw a diagram showing how methanol hydrogen bonds with itself. Include partial
charges on the appropriate atoms.
[3 marks]
δ+
δ−
H3 C
11.
H
O
δ−
O
CH3
Hδ+
Naturally occurring potassium consists of three isotopes with atomic masses and
abundances given below. Calculate the average atomic mass of naturally occurring
potassium.
[3 marks]
Isotope
Natural Abundance (%)
Isotopic Mass (amu)
39
93.26
38.9637
40
0.01
39.9640
41
6.73
40.9618
K
K
K
av. atomic mass = 93.26 × 38.9637 amu +
100
=
36.34 amu
+
av. atomic mass = 39.10 amu
0.01 × 39.9640 amu +
100
0.004 amu
+
6.73 × 40.9618 amu
100
2.76 amu
***2 decimal places therefore 4 sig. fig.**
Name: ________________________
12.
Student Number: _____________________
If a typical box of baking soda (sodium bicarbonate) contains 454 g, how many atoms of
oxygen are contained in the box of baking soda?
[4 marks]
sodium bicarbonate = NaHCO3
(84.006 g/mol)
atoms O = 454 g NaHCO3 × 1 mole NaHCO3 × 3 moles O
× 6.022 × 1023 atoms O
84.006 g NaHCO3 1 mole NaHCO3
1 mole O
atoms O = 9.76 × 1024 atoms O
***3 sig. fig.***
13.
Complete the following table. For charged species, place the charge(s) on the
appropriate atom(s) in the electron dot structure.
[9 marks]
Formula
Electron Dot Structure
Molecular Shape
Predicted
Bond Angle
trigonal planar
120˚
trigonal planar
120˚
linear
180˚
..
.. O ..
-1
SeO3
COCl2
N3-
14.
+2
..O.
.
Se
..O..
..
.. Cl
..
C
..
+
N
-N
..
...
O
.. .
-1
.. .
Cl
.. .
.. .N.
Is the molecule dibromomethane polar or nonpolar? Provide evidence by showing the
structure, dipoles and the approximate direction of the net dipole.
[4 marks]
Dibromomethane is polar:
Br
H
C
Br
H
net dipole
Name: ________________________
15.
Student Number: _____________________
Using the appropriate letter or letters, indicate the relationship(s) between the following
pairs of molecules. If more than one relationship applies, provide both letters.
A = stereoisomers
E = enantiomers
B = constitutional isomers
F = the same molecule
C = conformers
G = none of the above
D = diastereomers
[8 marks]
relationship(s)
CH3
H
CH3
OH
Cl
and
F
H
OH
F
Cl
Br
Br
CH3
SH
H
H
H
H
and
H3C
C
H3C
CH3
OH
H
SH
OH
F
H
F
and
CH3
A,D
OH
A,E
CH3
OH
O
H2N
and
OH
B
NO2
and
A,D
Name: ________________________
16.
Student Number: _____________________
A sample of ribose (MW = 150.13 g/mol) was analyzed and found to contain 40.00
percent C, 6.71 percent H, and 53.28 percent O. Determine the empirical and molecular
formula for ribose.
[5 marks]
There are several different ways to work through the logic for this question.
Any route that gets you the correct answers is valid.
1. Calculate the number of moles of each element in a sample of arbitrary mass.
A 100.00 g sample of ribose will contain 40.00 g C, 6.71 g H and 53.28 g O.
moles C = 40.00 g C × 1 mole C
moles H = 6.71 g H × 1 mole H
12.011 g C
1.0079 g H
moles C = 3.330 moles C
moles H = 6.66 moles H
moles O = 53.28 g O × 1 mole O
15.999 g O
moles O = 3.330 moles O
2. Use the moles of each element to generate a preliminary mole ratio.
moles C : H: O = 3.330 : 6.66 : 3.330
3. Divide all moles in the mole ratio by the smallest number of moles.
moles C : H : O = 1 : 2 : 1
4. Check that your mole ratio is all whole numbers. It is so we can use it to generate the
empirical formula:
Empirical formula = CH2O
5. Calculate the mass of the empirical formula (“empirical mass”).
mass CH2O = 12.011 g/mol + 2(1.0079 g/mol) + 15.999 g/mol
mass CH2O = 30.026 g/mol
6. Divide the molecular mass by the empirical mass.
number of empirical formula units in molecular formula = 150.13 g/mol
30.026 g/mol
=5
7. Multiply the empirical formula by this conversion factor.
Molecular formula = C5H10O5
17.
a)
For each equation below, assign oxidation states to each element, and identify which
atom(s) are oxidized and which are reduced.
[6 marks]
+5 -2 +6 -2
+1 +6 -2
0
+4 -2 +6 -2
+1 -2
+2 +6 -2
(VO2)2SO4 + 2 H2SO4 + Ni → 2 VO(SO4) + 2 H2O + NiSO4
oxidized: Ni
b)
-2 +1 -2 +1
reduced: V {of (VO2)2SO4}
+1 +7 -2
0 +1 -2
+1 +5 -2
+1 -2
CH3OH + KMnO4 → CH2O + KMnO3 + H2O
oxidized: C (of CH3OH)
reduced: Mn (of KMnO4)
Name: ________________________
18.
Student Number: _____________________
Give the complete IUPAC name for the following molecules, including stereochemistry
where applicable.
[6 marks]
A:
Br
(R)-cis-8-bromo-2,7,8-trimethyl-2,6-decadien-4-yne
O
O
O
B:
H
O
O
HO
4-sec-butyl-4-hydroxy-2,5,6-trioxo-3-propoxyheptanal
19.
Complete the following table.
[4 marks]
Formula
Name
Ba(HSO3)2
barium bisulfite
ZnI2
zinc(II) iodide
Fe(NO3)2
ferrous nitrate
Cs3N
cesium nitride
Name: ________________________
20.
Student Number: _____________________
Complete the following reactions by drawing the reactants or products. If no reaction
occurs write ‘no reaction’.
[10 marks]
+
H+
2CH3CH2CH2OH
CH3CH2CH2O
O
OCH2CH2CH3
OH
Br2
OH
no reaction
O
O
[O]
H or
H
OH
H
Br
Br
Br
Br
+
5Br2
Br
+
Br
3 Br2
Br
F
F
heat
Cl
F
Cl
F
pressure
Cl
SH
S
[O]
HS
S
OH
OH
+
H+
HO
H2O
HO
O
+
O
2H2O
Cl
Name: ________________________
Student Number: _____________________
O
O
H
HO
OH
+
H
H+
H
H
H2O
O
HO
HNO3
OH
no reaction
H2SO4
21.
(a)
[11 marks]
What is the maximum number of stereoisomers for 1-bromo-1,2-dichloro-2fluoroethane? 2 stereocentres therefore 22 = 4 possible stereoisomers
(b)
Draw all of these stereoisomers and assign a label to each (e.g. A, B, C, etc.).
Br
A:
Br
Cl
Cl
B:
Cl
Cl
F
(c)
Br
F
List all the pairs of enantiomers
A&B
C&D
(d)
List all the pairs of diastereomers.
A&C
A&D
B&C
B&D
C:
Br
Cl
Cl
F
D:
Cl
Cl
F
Name: ________________________
22.
(a)
Student Number: _____________________
Ammonia gas (NH3) reacts with oxygen gas to produce nitrogen monoxide gas and
gaseous water in an endothermic reaction. Assuming this is an equilibrium, write the
balanced chemical equation (include heat).
[3 marks]
4 NH3(g) + 5 O2(g) + heat
(b)
4 NO(g) + 6 H2O(g)
In what direction is the equilibrium shifted by the following changes:
[4 marks]
increase pressure:
add heat:
add oxygen:
remove nitrogen monoxide:
23.
LiOH + H2SO3
(a)
→
H2O + Li2SO3
Identify the acid and base on the reactant side of the equation above then identify the
conjugate species.
[6 marks]
acid:
H2SO3
conjugate acid:
base:
H2O
LiOH (or OH-)
conjugate base:
Li2SO3 (or SO32-)
(b)
Classify the acid on the reactant side of the equation as strong or weak.
weak acid
(c)
Classify the base on the reactant side of the equation as strong or weak.
strong base
24.
Calculate the concentration of a solution of HNO3 which has a pH of 4.12.
[3 marks]
HNO3 is a strong acid therefore concentration of HNO3 equals concentration of H+
pH = -log[H+]
[H+] = 10-pH
= 10-4.12
[H+] = 0.000076 mol/L = 7.6 × 10-5 mol/L
***2 decimal places in pH therefore 2 sig. fig. in [H+]***
Name: ________________________
25.
Student Number: _____________________
Draw the structures of the intermediate products for the following reaction sequence.
[8 marks]
H2
poisoned
Pd
CH3CH2O
H+
H+ H2O
H2 Ni
CH3CH2OH
heat
H+
+
HO
heat
HO
HBr
[O]
Br
no reaction
[O]
O
H+ H2O
HO
HO