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Grade 12 Chemistry Exam review
Short Answer
For the following questions, write the most appropriate answer in the space provided.
1. Explain why so many organic compounds (compounds of carbon and hydrogen) exist. Provide at least three
reasons.
2. What information does a correctly written structural formula provide?
3. Explain why an aldehyde with a low molecular weight has a lower melting point and boiling point than an
alcohol with a low molecular weight and the same number of carbon atoms.
4. Explain the significance of functional groups in organic compounds, in terms of classifying and naming the
compounds and in terms of the physical and chemical properties of the compounds. Provide examples to
support your answer.
5. Which of the following compounds best fits each description below?
butane, methanal, ethanoic acid, ethene, propanone
a) consists of atoms that all have a tetrahedral shape around them
b) has a trigonal planar shape
c) is the most soluble of these compounds in water
d) is commonly called acetone
e) is used to preserve animal tissue
6. Name all the aldehyde isomers that have the molecular formula CHO.
7. Why are amides polar?
8. Complete the following table by identifying an eight-carbon compound in each group.
Group
One structural formula
Name
Saturated/
unsaturated
alkyne
cycloalkane
alcohol
ether
9. Describe dispersion forces, and explain how they affect the physical properties of organic molecules.
10. State the steps you would take to determine whether or not a molecule has an overall molecular polarity.
Explain the significance of each step, and give an example.
11. Propanol may be oxidized to an aldehyde and then to an acid. Write the condensed structures and names of
the aldehyde and acid formed.
12. Write the condensed structure of the ester that is produced by the reaction of methanol and formic acid. Name
the ester.
13. State three functions of lipids in the human body.
14. Describe and explain the general trends in atomic radius in the periodic table.
15. Explain what the aufbau principle is and how it is used.
16. Explain what happens when an electron moves from n = 1 to n = 4. In your explanation, use the following
terms: absorption, emission, photons.
17. Outline the steps you would take to determine the molecular shape of a compound.
18. Using water as an example, differentiate between intermolecular forces and intramolecular forces.
19. What does VSEPR stand for? How is this theory used to predict molecular shape?
20. Draw the Lewis structure for SO2. How many bonded pairs of electrons and how many lone pairs of electrons
are around the sulfur atom
21. Draw orbital diagrams and Lewis structures to show how each pair of elements can combine. Write the
chemical formula of the product.
a) Al and Cl
b) Mg and O
22. Explain the difference between covalent bonding and polar covalent bonding, using an example of each.
23. What are the three different molecular shapes that can occur with a tetrahedral geometric arrangement of
electron groups?
24. The neutralization of nitric acid with potassium hydroxide has an enthalpy change of 53.4 kJ/mol. Write a
thermochemical equation for this reaction.
25. State Hess’s law in your own words, and explain how it is used.
26. Methane burns in oxygen to form carbon dioxide and water. This process releases 882 kJ/mol of methane.
a) Write the thermochemical equation for this reaction.
b) If 15.0 g of methane is burned, how much heat is released?
27. How does a catalyst affect the enthalpy change of a reaction?
28. Use the collision theory to explain the rate at which gas reactions usually occur.
29. The equilibrium constant for the following reaction is 2.0  104.
2HBr(g)  H2(g)  Br2(g)
a) Based on the equilibrium constant, which side is normally favoured?
b) What is the equilibrium constant for the reverse reaction?
30. List three different strategies that could be used to shift the following equilibrium toward the products.
2NOCl(g)  2NO(g)  Cl2(g)
31. Describe what happens on a molecular level when the concentration of one product in an equilibrium system
is increased.
32. Use the concept of equilibrium to explain the difference between a weak acid and a strong acid.
33. Label the conjugate acid-base pairs in each reaction.
a) NH3(aq)  H2O(l)  NH4+(aq)  OH(aq)
b) HF(aq)  H2O(l)  H3O+(aq)  F(aq)
34. Calculate the pH of a 0.000 25 mol/L solution of sodium hydroxide.
35. Write the equilibrium reaction and the equilibrium expression for the dissolving of calcium phosphate.
36. State one problem with the hydrogen fuel cell.
Problem
Graphics
For the following questions, use the graphics provided to review terms or skills. Add any missing labels, draw
any missing parts, or use the graphics to help you answer a question.
37. a) State the trends in the boiling points of straight-chain alkanes, as shown in the following graph, and explain
these trends.
b) Would your observations change if branched alkanes were included in this graph? Explain.
38. Complete the following table.
Name
2-fluoro-3,3-dimethylbutanal
Complete structural diagram
Class
4-methylpentanamide
meta-xylene
39. Draw the chemical reaction that links an alcohol to each organic compound. Identify the type of chemical
reaction.
a) aldehyde
b) ketone
c) carboxylic acid
d) ester
40. Use the following enthalpy diagram to write the thermochemical equation for the reaction.
41. Consider the following series of potential energy diagrams.
a) Which diagram represents the fastest reaction at room temperature? Explain your choice.
b) Which diagram represents the reaction of two solids at room temperature? Explain your choice.
42. Use collision theory to explain how temperature affects reaction rate. Include a diagram or graph to illustrate
your explanation.
43. Complete the following table, based on the following equilibrium system.
3H2(g)  N2(g)  2NH3(g)
H  92 kJ
Stress
decrease in volume
addition of inert gas at constant pressure
removal of NH3(g)
increase in temperature
Equilibrium shift
Critical Thinking
For the following questions, write the answer in the space provided. Use complete sentences in your answer.
If the question requires mathematical calculations, show all of your work. Write a final statement that gives
your solution.
44. Identify the class of organic compound that each substance in the following table belongs to.
Solubility
Hydrogen
Molecular
Substance in water
bonding
Melting point
polarity
a)
not soluble none
low for small molecules
non-polar
(usually gases at room
temperature)
b)
soluble
not with like low (lower than alcohols with polar
molecules
a similar number of carbon
atoms)
c)
extremely
strong
d)
extremely
very strong
e)
extremely
extremely
strong
low (lower than alcohols with polar
a similar number of carbon
atoms)
low (usually a liquid at room
very polar
temperature)
high (higher than alcohols with very polar
a similar number of carbon
atoms)
45. Write the electron configuration for each element or ion.
a) Au
b) Ni
c) Be2+
46. Consider the properties of the four substances in the following table. Which substance is most likely a
metallic solid? Justify your answer by explaining how the structure of a metal accounts for the properties
given.
Substance
A
B
C
D
Boiling point
2630°C
1770°C
2220°C
35°C
Electrical conductivity in solid and liquid states
poor conductor in both
conductive in liquid state but not in solid state
conductive in both liquid and solid states
poor conductor in both
Other properties
hard
hard
thermal conductor
soft
47. A chemist uses a coffee-cup calorimeter to neutralize completely 75.0 mL of 6.67 mol/L HCl with 75 mL of
NaOH. The temperature change is 39.6C.
a) Calculate the heat of neutralization, in kJ/mol of HCl.
b) Write a thermochemical equation for the reaction.
48. The iodine ion reacts very quickly with the hypochlorite ion.
OCl + I  OI + Cl
The data in the following table were collected for this reaction. What is the rate law for this reaction?
Trial
1
2
3
Initial concentration (mol/L)
[OCl]
[I]
1.7  103
1.7  103
3.4  104
1.7  103
3
1.7  10
3.4  104
Rate of formation of Cl (mol/Ls)
1.75  104
3.50  104
3.50  104
Grade 12 Chemistry Exam review
Answer Section
SHORT ANSWER
1. ANS:
Carbon can form four bonds to other atoms. These other atoms include carbon, hydrogen, oxygen, nitrogen,
and the halogens. Carbon atoms may form chains (with or without branches), cyclic structures, and double
and triple bonds. Each different bonding arrangement results in different physical and chemical properties.
PTS: 1
2. ANS:
The structural formula indicates what functional groups are in the molecule and how the bonds are arranged.
PTS: 1
3. ANS:
The alcohol has a hydroxyl group, or OH bond, but the aldehyde does not. The alcohol is therefore more
polar than the aldehyde. It can participate in hydrogen bonding, but the aldehyde cannot. There are stronger
forces of attraction between the alcohol molecules than between the aldehyde molecules.
PTS: 1
4. ANS:
Organic compounds are named and classified according to their functional groups. For example, alcohols are
a class of compounds that have a hydroxyl functional group. Compounds with the same functional group have
similar physical and chemical properties. Alcohols are soluble in water and form hydrogen bonds with water
molecules. They are liquids at room temperature, and they are flammable.
PTS: 1
5. ANS:
a) butane
b) ethene, methanal
c) ethanoic acid
d) propanone
e) methanal
PTS: 1
6. ANS:
pentanal, 3-methylbutanal, 2,2-dimethylpropanal, 2-methylbutanal
PTS: 1
7. ANS:
A nitrogen atom attracts electrons more strongly than a carbon or hydrogen atom, so the carbon-nitrogen and
the nitrogen-hydrogen bonds are polar.
PTS: 1
8. ANS:
Group
One structural formula
Name
Saturated/
unsaturated
alkyne
octyne
unsaturated
cycloalkane
cyclooctane
saturated
alcohol
1-octanol
saturated
ether
ethoxyhexane
saturated
Other answers are possible for the alcohol and the ether.
PTS: 1
9. ANS:
Dispersion forces are very weak intermolecular forces that exist between molecules. When a carbon atom is
bonded to another carbon atom, or to a hydrogen atom, the bond is not considered to be polar because the
electronegativity difference between carbon atoms is zero and between carbon and hydrogen atoms is very
small. As a result, the molecules experience very weak forces of attraction for other, similar molecules. The
larger the molecule, the more attraction there is, but the attraction is still very weak. Molecules that have only
weak intermolecular forces between them generally have very low melting and boiling points.
PTS: 1
10. ANS:
a) Determine whether or not polar bonds are present in the molecule by looking at the electronegativity
differences (the ability to attract electrons) between the atoms within the molecule. High electronegativity
differences (very polar bonds) between the atoms result in a bond dipole: a partially negative charge and a
partially positive charge, separated by the length of the bond. An alcohol is a good example of a polar
molecule, with the OH bond establishing regions that have partially negative and partially positive charges.
b) Consider the shape of the molecule. Is there a region with a partial negative charge and a region with a
partial positive charge, not balanced by other, similar regions? Polar bonds exist between carbon and
chlorine in a carbon tetrachloride molecule, but the shape is tetrahedral. This shape minimizes the electron
repulsion forces within the molecule, so one region of the molecule does not appear more negative than
any other region.
PTS: 1
11. ANS:
CH3CH2CHO, propanal; CH3CH2COOH, propionic acid
PTS: 1
12. ANS:
CHO–O–CH3, methyl formate
PTS: 1
13. ANS:
1) They store energy.
2) As hormones, they regulate body functions.
3) They protect vital body organs against extremes of heat and cold.
PTS: 1
14. ANS:
Atomic radius increases as you go down a group of elements in the periodic table. This trend is a result of
increasing numbers of electrons occupying increasing numbers of energy levels. The effective nuclear charge
changes only slightly and therefore does not offset the increase in size due to the increase in energy levels.
Atomic radius decreases as you go left to right across a period in the periodic table. The valence
electrons are found in orbitals of the same energy level. At the same time, the effective nuclear charge is
increasing with the increase in nuclear charge, which results in a greater force of attraction pulling the valence
electrons closer to the nucleus. Thus, atomic size decreases.
PTS: 1
15. ANS:
The aufbau principle is the imaginary process of building up the ground state electron structure for each atom,
in order of atomic number. When determining the electron configuration of an element, the electrons are
written sequentially in orbitals of increasing energy, starting with the electron in the 1s orbital.
PTS: 1
16. ANS:
When an electron moves from n = 1 to n = 4, the electron absorbs a photon of energy that is equal to the
difference in energy between the two levels.
PTS: 1
17. ANS:
1) Draw a Lewis structure of the molecule.
2) Determine the number of pairs of valence electrons around the central atom
3) Determine which one of the five geometric arrangements can accommodate this total number of electron
groups.
4) Determine the molecular shape from the positions occupied by the bonding pairs and lone pairs.
PTS: 1
18. ANS:
Intermolecular forces are forces between molecules. Water has hydrogen bonds, dipole-dipole forces, and
dispersion forces that hold adjacent water molecules together. Intramolecular forces are forces within a
molecule. They hold the atoms together within the molecule. Each water molecule has polar covalent bonds
between the hydrogen atoms and the oxygen atom.
PTS: 1
19. ANS:
VSEPR stands for Valence-Shell Electron-Pair Repulsion. The VSEPR theory is used to predict the shapes of
molecules by relating the total number of electron groups around the central atom to a geometric arrangement
that minimizes the repulsions of these electron groups. For example, two electron groups arrange themselves
in a linear position, with bond angles of 180.
PTS: 1
20. ANS:
There are three bonded pairs of electrons and one lone pair of electrons around the sulfur atom.
PTS: 1
21. ANS:
a)
The product is AlCl3.
b)
The product is MgO.
PTS: 1
22. ANS:
Covalent bonding exists when the bonding electrons are shared equally or nearly equally, as in molecules of
O2 and N2. Polar covalent bonding exists when there is unequal sharing of a pair of electrons between two
atoms, as in HCl and H2O.
PTS: 1
23. ANS:
tetrahedral, trigonal pyramidal, and angular (bent)
PTS: 1
24. ANS:
Since the enthalpy change is negative, the reaction is exothermic. Therefore, the energy term is written on the
product side of the reaction equation.
HNO3(aq)  KOH(aq)  KNO3(aq)  H2(l)  53.4 kJ
PTS: 1
25. ANS:
Hess’s law states that if a chemical reaction can be expressed as the algebraic sum of two or more reactions,
then the enthalpy term is the sum of the enthalpy changes for all of the reactions added.
Equations are reversed and/or multiplied so that, when algebraically combined with other equations, they will
yield the desired reaction. The enthalpy change for each reaction is changed in the same way as the chemical
equation before being added to the other enthalpy changes. Note: Students may find it easier to answer this
question by using an example.
PTS: 1
26. ANS:
a) CH4(g) 
O2(g)  CO2(g)  H2O(g)  882 kJ
b)
Burning 15.0 g of methane releases 825 kJ of heat.
PTS: 1
27. ANS:
A catalyst does not affect the enthalpy change of a chemical reaction. A catalyst increases the rate of a
chemical reaction by decreasing the activation energy required, but it does not affect the difference in
enthalpy between products and reactants.
PTS: 1
28. ANS:
Particles in the gaseous state move much faster than particles in the solid or liquid state. They have a higher
kinetic energy. This allows a greater percent of all collisions to be successful. Because gas reactants exist as
elementary molecules or atoms, the bonds that hold the molecules or atoms together in the liquid or solid state
do not have to be broken. Therefore, lower activation energy is required. The rapid movement of individual
molecules or atoms provides maximum surface area for interaction. All these factors combine to make
gaseous reactions extremely fast.
PTS: 1
29. ANS:
a) Since the equilibrium constant is greater than 1, the equilibrium favours the products.
b) The equilibrium constant for the reverse reaction is the inverse of the equilibrium constant for the forward
reaction.
PTS: 1
30. ANS:
1) Increase the concentration of NOCl(g).
2) Decrease the concentration of either NO(g) or Cl2(g).
3) Decrease the pressure.
PTS: 1
31. ANS:
When the concentration of one product is increased, there is an increased chance for collisions between
product particles. There is not an immediate increase in collisions between reactant particles. Thus, the rate of
the reverse reaction is temporarily greater than the rate of the forward reaction. This results in the production
of more reactants. The equilibrium shifts to the left.
PTS: 1
32. ANS:
The strength of an acid is related to the value of the equilibrium constant of the acid in an aqueous solution.
Strong acids have equilibrium constants that are greater than 1 and ionize completely.
PTS: 1
33. ANS:
a) NH3(aq)
base 1
b) HF(aq)
acid 1


H2O(l)
acid 2
H2O(l)
base 2


PTS: 1
34. ANS:
pOH  log[OH]
 log(0.00025)
 3.60
pH  14  pOH
 14  3.60
 10.40
PTS: 1
35. ANS:
Ca3(PO4)2(s)  3Ca2+(aq) + 2PO43 (aq)
Ksp = [Ca2+(aq)]3[PO43(aq)]2
PTS: 1
36. ANS:
NH4+(aq)
conjugate acid 1
H3O+(aq)
conjugate acid 2


OH(aq)
conjugate base 2
F(aq)
conjugate base 1
The hydrogen fuel cell requires hydrogen fuel or uncombined hydrogen, which is not found naturally on
Earth. Processes that produce hydrogen from petroleum or methane contribute significantly to pollution
problems.
PTS: 1
PROBLEM
37. ANS:
a) Based on the graph, as the molecular masses of straight-chain alkanes increase, the boiling points also
increase. The boiling points do not increase by a constant factor, however. (The graph is curved.) Alkanes
contain only non-polar carbon-carbon bonds and carbon-hydrogen bonds. Thus, the boiling points are only
affected by molecular mass and shape. Since these are straight-chain alkanes, only mass should affect the
boiling points. With this in mind, more kinetic energy (a higher temperature) is needed to separate larger
molecules than to separate smaller molecules. The increase in boiling point is larger for molecules with
smaller molecular masses (fewer CH2 units), since each additional CH2 unit represents a larger fraction of
the total molecule.
b) Yes. Differences in molecular shapes result in isomers. The branched compounds are more compact and do
not become entangled with each other, resulting in lower intermolecular forces and thus lower boiling
points.
PTS: 1
38. ANS:
Name
2-fluoro-3,3-dimethylbutanal
Complete structural diagram
Class
aldehyde
methyl-3,3,4-trimethylpentanoate
ester
4-methylpentanamide
amide
meta-xylene
aromatic
PTS: 1
39. ANS:
PTS: 1
40. ANS:
4HCl(g)  O2(g)  2Cl2(g)  2H2O(g)  120.2 kJ
PTS: 1
41. ANS:
a) C: It has the lowest activation energy barrier, therefore a greater percent of the particles have sufficient
energy for a successful collision.
b) B: Two solids have the highest activation energy barrier because more bonds have to be broken to form
products.
PTS: 1
42. ANS:
As the Maxwell-Boltzmann distribution diagram shows, the number of particles with energy that is equal to
or greater than the activation energy is increased. This increases the number of successful collisions, thereby
increasing the reaction rate.
PTS: 1
43. ANS:
Stress
decrease in volume
addition of inert gas at constant volume
removal of NH3(g)
increase in temperature
PTS: 1
Equilibrium shift
to the right
no effect
to the right
to the left
44. ANS:
a) alkane
b) ether
c) amine
d) alcohol
e) organic acid
PTS: 1
45. ANS:
a) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d9
b) 1s2 2s2 2p6 3s2 3p6 4s2 3d8
c) 1s2
PTS: 1
46. ANS:
Substance C is a metallic solid because it is an electrical conductor in both the solid and liquid states. It is also
a thermal conductor. The conductivity of substance C can be explained by the delocalized valence electrons,
which are mobile and free to move throughout the array of positive ions.
PTS: 1
47. ANS:
a)
Qreaction  Qgained by solution
nHr  mcT
0.0750 L  6.67 mol/L HCl  0.500 mol HCl
Hr  (150.0 g  4.184 J/gC  39.6C)  0.500 mol
 49.8 kJ
b) HCl(aq)  NaOH(aq)  NaCl(aq)  H2O(l)  49.8 kJ
PTS: 1
48. ANS:
Compare trials 1 and 2: Doubling the concentration of OCl causes the reaction rate to double. Therefore, the
reaction rate is first order with respect to the concentration of OCl.
Compare trials 1 and 3: Doubling the concentration of I also causes the reaction rate to double. Therefore, the
reaction rate is first order with respect to I.
Reaction rate  k[OCl]1[I]1
PTS: 1