PART 1: ACIDS & BASES
(AP Chemistry)
Questions by Miha Lee
Corrected by Jay Stern but he didn’t give me the score.
Instructions: Classify each of the following questions as being either: Knowledge,
Comprehension, Application, Analysis, Synthesis or Evaluation.
Type of
Reasoning
Question
Knowledge
(1) Which of the following is not a definition of an acid?
a. any chemical compound that, when dissolved in
water, gives a solution with a pH less than 7.0.
b. a compound which donates a hydrogen ion (H+) to
another compound.
c. An aqueous solution that has more hydroxide ions
than hydrogen ions.
d. an acid is a substance that increases the
concentration of hydronium ion (H3O+) when
dissolved in water.
Answer) c
An acidic solution has more hydrogen ions than hydroxide
ions.
Comprehension
(2) Explain why the pH scale of a water solution at 25C
ranges from 0 to 14.
Answer) According to Arrehnius definition, an acid is a
substance that increases the concentration of hydronium
ion (H3O+) when dissolved in water, while bases are
substances that increase the concentration of hydroxide
ions (OH-). On the other hand, water has an ion product
equilibrium constant (Kw) of 1.4 X 10-14 at 25C. The pH is
the negative log of the concentration of H+. pH = -log[H+]
To keep the ion product equilibrium constant of water (Kw),
the concentration of H+ can change only in a range from 1
to 10-14. Therefore, the pH values can be only form 0 to 14.
(I don’ t agree with the answer as written. The equilibrium
Assignment 1 – p. 1
constant needs better explanation.
For example, The
equilibrium constant for water is 1.8 x 10 – 16 because in
pure water it is calculated from the mole concentration of
water or about 55.6 moles/liter. The activity of the water
is the amount that self-ionizes.
Based on resistivity
measurements of pure water, this is approximately 1 x 10 –
7
for each of the hydrogen ion concentration and hydroxyl
ion concentration. Then Kw = Keq [H2O] = [H+][OH-] =
1.0 x 10-14. That is, the concentration of each [H+], [OH-]
is the square root of 1.0 x 10-14 ,that is 1.0 x 10 – 7 in pure
water at 25 oC. (If the temperature changes, so does the
pH.) If additional protons are added, the system adjusts by
reducing the number of hydroxyl ions so the total
concentration of +/- ions is 1.0 x 10-14. (CAUTION: This
concept of pH is based on relatively dilute solutions.
Concentrated acid solutions of – 1 or – 2 are well known. )
Because it is easier to work with whole, positive numbers,
the pH scale was devised. It is related to the hydrogen ion
concentration as follows:
pH = -log[H+], at 25 oC.
Similarly the pOH = -log[OH-]. In pure water at 25 oC, pH
+ pOH = 7 + 7 =14.
The point is, explaining pH is really quite involved. Your
answer does not have to be extremely technical, but it
needs improvement over what you wrote.)
In Korean high school chemistry, Kw is used a kind of equlibirum
constant for water because the concentration of water is almost
constant in terms of significant numbers. My idea for this question is to
find out if students understand why the pH scale has the range of 0 to
14 at 25 oC and the pH scale can vary with the temperature. Jay’s
explain is correct but this question is open ended, and thus the level of
answers can be diverse.
Application
(3) When a drop of BTB (bromothymol blue) solution is
added to vinegar, what color does the vinegar turn?
a. Yellow
c. Blue
b. Green
d. No change
Answer) a.
Vinegar is acidic, and BTB turns yellow in an acidic
solution.
Assignment 1 – p. 2
Analysis
(4) An acid expressed as HA is dissolved in water yielding
a 0.1M solution. The resulting pH of the solution is 5.0.
Which of the following is not true? (at 25C)
a. The degree of ionization () is 0.0001.
b. The concentration of A- is 1×10-9mol/L.
c. Ionization constant (Ka) is 1×10-9.
d. The concentration of H3O+ is 1×10-5mol/L.
e. The concentration of OH- is 1×10-9mol/L.
Answer) b.
HA

H+ + A 0.1 – x
x
x
-5
x = 10 M because the pH is 5.
Ka = x2/0.1 = 1×10-9
pOH = 14-pH = 14-5 =9 (at 25C)
The concentration of A- is 1×10-5mol/L.
Synthesis
(5) Explain why clean rainwater has an acidic pH (5.6 at
25C).
Answer) Clean air includes CO2 (about 0.038%). When this
CO2 dissolves in rainwater, it becomes carbonic acid,
which makes rainwater slightly acidic.
(If you are going to be precise regarding the amount of
carbon dioxide is in the air, and state a pH, then the steps
to the answer need to be shown. Otherwise, the question
should just be “ Why does rainwater have an acidic
pH?” )
Evaluation
(6) Which one is more acidic? A sulfuric acid solution,
which has a pH of 6 or an acetic acid solution that has a
pH of 4.
Answer) An acetic acid solution with the pH of 4. Because
the lower the pH, the more acidic the solution is. (Sulfuric
acid disassociates completely in water. That is why it is
a “ strong” acid.
Acetic acid, CH3COOH, does not
disassociate completely. Need to expand answer.
Otherwise, it is not “ evaluative.” )
I don’ t feel to expand the answer. Just because an acid is
strong doesn’ t mean it is more acidic than other weak
acid with high conceptnration. That is my point.
Assignment 1 – p. 3
PART 2: CHEMICAL BONDING
(AP Chemistry)
Questions by Miha Lee
Instructions: Classify each of the following questions as being either: Knowledge,
Comprehension, Application, Analysis, Synthesis or Evaluation.
Type of
Reasoning
Knowledge
Question
(1) What kind of chemical bond is the following statement
describing?
It is an electrical attraction between two oppositely charged
particles. It is a bond formed by transfer of electrons
between atoms or group of atoms.
Answer) ionic bond
(Answer should say it is a bond formed when one atom or
group of atoms donates electrons to an atom or group of
atoms which accepts them. The atoms start out neutral
because their charge is balanced by protons in the nucleus.
They become charged when they form a bond which is then
disrupted by, for example, solvation.)
I think Jay’ s correction should be a part of the question. So I
adjusted my question to be more clear.
Comprehension
(2) In your own words, explain why ionic compounds are
hard but brittle.
Answer) Ionic bonds are strong bonds, which makes ionic
compound hard. However, when a force is exerted on an
ionic compound, it is subject to be brittle due to the crystal
lattice structure. The ions in the crystal lattice cannot move
very much without disturbing the overall balance between
negative and positive charges. If one layer of ions is moved,
the result is a buildup of repulsive forces within the crystal
structure, and the entire structure falls apart.
(Ionic bonding produces a crystalline structure that cannot
really be identified as “ molecular.” Electrons are donated
between ions resulting in a rigid, typically 3-dimensional
framework.
The crystalline structure can be shattered
(cleaved) by force. This compares to metallic bonding in
Assignment 1 – p. 4
which the electrons are held in common by the atoms. It
allows the substance to be formed without shattering.
Covalent bonding is similar in that regard to metallic bonds,
but shares electrons. The sharing produces bonds that may
be less strong than ionic bonds but are able to absorb
energy more readily.)
I don’ t agree with Jay. Covalent bond in which bonding
electrons are shared by two atoms is stronger than an ionic
bond. Only the inter molecular bonds between molecules are
weaker than ionic bonds. And my point of question is to find
out the depth of understanding about ionic compound.
Application
(3) Why can a metal conduct electricity?
a. A metal has movable cations.
b. A metal has movable anions.
c. A metal has movable electrons.
d. A metal has movable a nucleus.
Answer) c
Analysis
Synthesis
(4) Both carbon dioxide and a diamond have covalent bonds.
But carbon dioxide is a gas and a diamond is a solid at STP
condition. Compare and contrast two materials in terms of
chemical bonding.
Answer) Carbon dioxide has a molecular structure by forming
strong four covalent bonds between the atoms. However,
there are weak bonds between CO2 molecules. (why? Need
more info.)
In contrast, diamonds are giant molecular lattice
structures. This implies that strong covalent bonding holds
their atoms together in a highly regular extended network.
The bonding between the atoms goes on and on in three
dimensions. Melting requires the separation of the species
comprising the solid state. Because of the large amount of
energy needed to break huge numbers of covalent bonds, all
giant covalent network structures such as diamonds have
high melting points.
(generally O.K.)
(5) Determine the shape of CH4 molecule based on the
valence shell electron pair repulsion theory.
Answer) tetrahedron (This answer needs an illustration.)
A CH4 molecule has same four covalent bonds between C
Assignment 1 – p. 5
and H. And there is no non-bonding electron pair around the
center atom C. According to VSEPR, same four electron
pairs repel each other so that they make a shape of
tetrahedron.
Evaluation
(6) Which of the following does not contribute to determining
the polarity of a molecule?
a. The presence of bonding pair of electrons
b. The polarity of each bond
c. The shape of a molecule
d. The presence of nonbonding pair of electrons
Answer) a (“ b” is not a good answer. It needs to
acknowledge that different atoms bonded to a central atom
will result in a dipole.) He misunderstood my question. That
is exactly same as I think. A bond between the same atoms
is non-polar and a bond between different atoms is polar.
However, even a molecule has polar bonds, it can be nonpolar molecule by the shape of a molecule that valence the
polarities of its bonds.
Assignment 1 – p. 6
PART 3: CHEMICAL EQUILIBRIUM
(Chemistry II)
Questions by Miha Lee
Instructions: Classify each of the following questions as being either: Knowledge,
Comprehension, Application, Analysis, Synthesis or Evaluation.
Type of
Reasoning
Knowledge
Question
(1) Which of the following factors of a system can change the
equilibrium constant of a reaction?
a. pressure
b. concentration
c. temperature
d. particle size
Answer) c
Comprehension
(2) Which is the equilibrium constant of the following reversible
reaction?
2A(g) + B(g)  2C(g)
a. K = [C]2/ [A]2[B]
c. K = [A]2[B] /[C]2
b. K = [C]/ [A]2[B]
d. K = [C]2/ [A][B]
Answer) a. K = [C]2/ [A]2[B]
(Miha, to demonstrate “ comprehension,” this is inadequate.
It would be best as a multiple-choice question.(I don’ t
understand why?) If you want to keep this format, then
consider writing your question as follows: “ In a reversible
chemical reaction at equilibrium, the rate forward equals the
rate backward. A mathematical statement expressing this
relationship defines the equilibrium constant. Given the
reaction 2A(g) + B(g)  2C(g), show the definition for its
equilibrium constant.”
Answer: K = [C]2/ [A]2[B] )
I agree with Jay. But in a chemical equation, the arrow ->
means reversible reaction.
Application
(3) Using the following equation, calculate the equilibrium
constant.
Assignment 1 – p. 7
N2(g) + 3H2(g)  2NH3(g)
A one-liter vessel contains 1.60 moles NH3, 0.80 moles N2, and
1.20 moles of H2 at equilibrium. What is the equilibrium
constant of this reaction?
Answer) 1.85
K = [NH3]2 / [H2]3[N2] = [1.6]2 / [1.2]3[0.8]
(Miha, I advise the following:
(3) A one liter vessel contains the following:

1.60 moles NH3

0.80 moles N2

1.20 moles H2
The mixture is at equilibrium. Write and balance the chemical
equation that defines the reaction. Which is the forward
reaction? Then calculate the equilibrium constant. Show your
work.
Ans: N2(g) + 3H2(g)  2NH3(g)
Keq =
[NH3]2 / [N2] [H2]3 = [1.60] 2 / [0.80][1.20]3
Keq = 1.85
I don’ t want to assess student’ s ability to balance a chemical
equation in this question because it is not relevant to the
chemical equilibrium. And if they use 2NH3(g) N2(g) +
3H2(g) , the equilibrium constant is 1/1.85, that is 0.54.
Analysis
(4) The following system is at equilibrium.
3NO(g)  N2O(g) + NO2(g) + 154.9 kJ
To shift the equilibrium position toward right, what should
we do?
a. The temperature should be lowered.
b. The pressure should be lowered.
c. The concentration of NO2 should be lowered.
Assignment 1 – p. 8
d. The concentration of NO should be lowered.
Answer) c
(Miha – this is a good question.)
Synthesis
(5) The graph
shows the
relationship
between reaction
time and the
molarity of
reactants and
products.
Determine the
equilibrium
constant definition,
then solve and
identify which of the following answers is correct.
a. 1.6
b. 4
c. 64
d. 128
Answer) c
H2(g) + I2(g)  2HI(g) according to the graph.
K = [HI]2 /[H2][I2]
= [1.6]2 /[0.2][0.2] = 64
Evaluation
(6) To use a dry-board marker for a longer time, we need to
recap it as soon as possible after we use it. Explain the
reason for this in terms of chemical equilibrium.
Answer) The marker consists of a colorant on a wick
suspended in a fast-evaporating solvent. When the marker is
capped, the solvent vapor is in equilibrium with its liquid
phase. If the marker is not capped after use, it cannot reach
equilibrium because the vapor evaporates from the wick and
dissipates into the surroundings.
(Miha – I corrected grammar and syntax, but the question is
very good.)
Assignment 1 – p. 9
Refelection on the reasoning questions.
Although I have many experiences with generating questions, this
assignment was a valuable opportunity for me to learn the importance of
creating questions that ask higher-level order thinking skills. It was hard but
rewarded. For me, generating synthesis level questions is the most difficult
part. It requires a number of considerations. It will be difficult for my students,
too. I want to be more creative in generating higher-level thinking order
questions. I will make a lot of effort to improve my skills when I go back to
teach chemistry.
My partner Jay made a lot of contribution to improve my skills. I learned a
lot form his questions. However, as I am a Korean and my English is poor,
there seemed to be some communication problems between us. My question
style seemed to bother him a lot. So it took such a great deal of time for him to
revise my questions. That is why I turned in this assignment so late. Sorry
about that to Jay and Dr. Herr.
Assignment 1 – p. 10