Final exam,
Question 1
The molecule nitro-methane has the formula CH3NO2.
Apply Lewis theory to calculate the most likely electronic structure for this molecule, consider the
oxidation state and the formal charge of the nitrogen atom and select the correct statement.
A. The oxidation number of N is +1, whereas the formal charge is +3
B. Nitro-methane should be a liquid or solid at room temperature because of its strong hydrogen
bonding
C. The compound is a moderately strong Arrhenius acid
D. Lewis theory would predict two different N-O bonds of unequal length, but molecular orbital
theory would predict two identical bonds with bond order 1.5
E. One mole of nitro-methane contains four moles of atoms and three moles of lone pairs
Question 2
In the recent nuclear calamity in Japan the reactor workers wore suits to protect themselves from
emitters of alpha particles, like the isotope 239Pu. The alpha component of the radiation cannot even
penetrate the human skin, but it can be very harmful if released inside the body after ingestion or other
penetration. Alpha particles consist of four nucleons: two protons and two neutrons. Select the correct
statement
A. Once the plutonium atom has lost an alpha particle by emission what is left is 235Pu
B. When an alpha particle is combined with four electrons it forms an atom of the element
Beryllium. This process is called reduction
C. Alpha emission by radioactive ores produces helium-4
D. A and B are true
E. A and C are true
Question 3
What contains the largest number of protons?
A.
B.
C.
D.
E.
One mole of 3He gas
0.2 mole of Ne gas
1/6 of a mole of solid LiF
One mole of 1H2 hydrogen gas
They all contain the same number of protons
Questions 4-13
The formiate (aka formate or methanoate) ion HCOO- is the conjugate base of the simplest carboxylic
acid. However, its electronic structure has a complication because Lewis theory would predict two
O
O
C
O
H C
–
H
O
–
–
“resonance structures”
A molecular orbital diagram limited to the three pz orbitals and the four electrons involved in the
resonance looks something like the following
O
C
O
Ground state
Excited states
True or False?
4) The MO denoted Ψ2 is a non-bonding orbital. It has a vertical nodal plane that passes through the
central carbon atom
5) The excited state in the middle follows the rule of Hund and is paramagnetic
6) As drawn on the left side of the MO diagram, the pz orbital of the carbon atom contributes equally to
Ψ1 and Ψ3. This cannot be quite correct because oxygen is more electronegative than carbon
7) The excited state on the right has a higher bond order than the one in the middle and represents a
neutral species rather than an anion as one electron has reached the vacuum continuum
8) The excited state in the middle would result in the disintegration of the CO2 group as the bond order
is zero for both C-O bonds
9) In a description in terms of hybridization the central carbon atom is best assumed to have “sp”
hybridization
10) The one proton left on the formiate ion is strongly acidic
11) The bonding shown in the MO diagram has σ rather than π character
12) The resonance denoted by the arrow in the top diagram represents a relatively slow process,
but at higher temperatures it becomes more rapid as the rising thermal energy overcomes its activation
energy
13) In the Lewis structures the negative charge of the anion is always localized on the one oxygen atom
that has an extra lone pair, but in the MO description both oxygen atoms have a charge of –½ because
the charge distribution of the occupied MO’s is symmetrical around the central C-atom.
Question 14
Consider the azide ion N3-1. Its general shape is X-X-X. A number of Lewis structures are possible. Do a
Lewis calculation and select the correct statement
A. All the possible Lewis structures involve an “sp2” hybridization for the central atom
B. Because the central atom lacks a lone pair in the most favorable Lewis structure, the shape of
the molecule is linear
C. There are two Lewis structures with a triple bond that form a resonance pair. They are the best
choice for the electronic structure because their formal charges are minimal
D. All of the above statements are true
E. None of the above statements are true
Question 15
One mole of Titanium(III)chlorite contains:
A.
B.
C.
D.
E.
4 moles of atoms
7 moles of atoms
10 moles of atoms
13 moles of atoms
16 moles of atoms
Question 16
Once ignited, magnesium metal reacts readily with oxygen to form the solid oxide MgO. An excess of the
metal is brought into a sturdy metal bomb and the bomb is filled with a gas mixture consisting of oxygen
and argon. The partial pressure of both gases is 2 Atm initially and the temperature is 20oC. The metal is
ignited to form the oxide. Heat is allowed to flow into a heat sink formed by a large water bath until the
temperature is back to its initial value. This occurs after 6 kJ of heat is transferred to the heat sink.
The molar enthalpy of combustion of magnesium is -600kJ/mole for the combustion reaction:
Mg + ½O2 MgO
A. Although the entropy change in the reaction is negative the entropy of the universe has
increased (due to the heat transfer to the outside world)
B. The amount of oxygen that reacted is 0.005 mole of O2
C. The final pressure in the bomb is 2 Atm
D. All of the above
E. None of the above
Note: the difference in volume between metal and its oxide can be neglected. PV=nRT; R=8.413 J/K.mol
Question 17
John has made a solution of a salt, but he forgot to label it. He knows the salt is either: sodium chloride,
silver perchlorate or lead acetate. He decides to take a small quantity (“aliquot”) and mix with small
amounts of solutions, the composition of which he is certain of:
Mixing with NaOH solution produces a white precipitate, while mixing with a dilute H2SO4 solution also
produces a white precipitate plus a faint smell of vinegar
A.
B.
C.
D.
E.
His unknown solution is silver perchlorate
His unknown solution is lead acetate
His unknown solution is sodium chloride
His results are inconclusive: his unknown could still be either silver perchlorate or lead acetate
John is completely confused because his solution cannot be any of the above mentioned
Question 18
One or more of these statements are correct. Select a correct one.
A. The HSe- cation is the conjugate base of the Se2- cation
B. Sulfur dioxide is considered acidic according to both Lavoisier and Lewis
C. The electrochemical potential of Ag+/Ag is +0.8 V and of Cd2+/Cd -0.4V, therefore a rod of
cadmium metal will precipitate silver out of a silver nitrate solution when immersed
D. At a cathode electrons are taken up from the solution and transported away from it
E. The oxidation state of oxygen in Na2O2 is -2
Question 19&20
Wikipedia gives the following Eө values for a number of standard reduction potentials:
Cs+ + e−
Eө =
+ 2 H+ + 2 e−
(p-benzoquinone)
−3.026 V
Eө =
Cs(s)
+0.6992 V
(hydroquinone)
BrO4− + …X……
BrO3− + …Y…..
Eө =
+1.85 V
F2(g) + 2 H+ + 2 e−
2 HF(aq)
Eө =
+3.05 V
The cesium and fluorine redox couples only serve as a frame of reference. Hint: Make sure you
balance the perbromate/bromate half reaction first. Then combine the two redox couples.
19) Consider the benzoquinone/hydroquinone and perbromate/bromate half-reactions and select the
correct statement
A. The reaction of perbromate with hydroquinone is spontaneous
B. In the quinone half reaction the oxidation number (OX) of the oxygen atoms remains the same,
but the OX of the carbon atoms to which they are attached does change
C. The bromate/perbromate half reaction involves only one electron
D. Both A and B are true
E. All answers above are true
20) Consider the benzoquinone/hydroquinone and perbromate/bromate half-reactions and select the
correct statement
A. In a direct spontaneous redox reaction, involving the appropriate quinone and bromine species
in one vessel the pH would remain constant
B. The voltage of a galvanic cell would be about +1.15V and the anode is found in the quinone halfcell.
C. In a galvanic electrochemical cell involving the quinone half reaction in one cell and the bromine
containing species in the other, the pH would drop in the quinone half-cell but rise in the other
cell
D. All statements above are true
E. None of the above statements are true
Question 21
The common names for these two forms of
C5H12 are n-pentane on the left and
neopentane on the right.
Select the correct statement
A.
B.
C.
D.
E.
The primary carbons have an oxidation number of +1 and the quaternary carbon of -4
The IUPAC name of neopentane is (2,2)-dimethylpropane (or simply dimethylpropane)
Both compounds are carbohydrates
All of the above
None of the above
Question 22
Which of the 5 elements in the set is the most electronegative?
A: Beryllium
B: Barium
C: Boron
D: Bromine
E: Bismuth
Question 23
This molecule is called anthracene.
A.
B.
C.
D.
E.
The molecule can also be written as C13H12
The molecule is aromatic and non-polar
All carbon atoms can be described with sp3 hybridization.
None of the above
All of the above
Question 24
Which of the 5 elements in the set is the least electronegative?
A: Chromium
B: Cerium
C: Cesium
D: Calcium
E: Chlorine
Question 25
Select the correct chemical formula
sodium sulfide
A: KSO4
B: K2SO4
C:Na2S
D:NaS2
E:Na2SO3
Question 26
The following experiment is used to determine the amount of argon gas in the container. In the
experiment
V = 5.000 L
h = 333 mm.
t = 35° C
Pbar = 730 torr. (Atmospheric pressure at the moment of the experiment)
PHe =
pressure of the Argon
nHe =
number of moles Ar
R= 0.08204
[L.atm/K.mol]
=8.314 [J/K.mol]
1Atm=760 torr
The tube is filled with mercury. Determine the following for the argon gas:
A) PAr= 0.26 Atm, nAr=0.055 mol
B) PAr= 0.52 Atm, nAr=0.103 mol
C) PAr= 1.76 Atm, nAr=7.66 mol
D) PAr= 1.40 Atm, nAr=0.28 mol
E) None of the above
Question 27
Iron(II)oxide FeO is a a major component of rust. Its crystal
structure is shown. The larger spheres are the iron atoms
A.
B.
C.
D.
E.
The coordination number of Fe(II) in FeO is 6.
FeO has a sodium chloride type structure
FeO has a cesium chloride type structure
Both A and B are true
Both A and C are true
Question 28
Select the correct chemical formula
nickel(II) phosphide
A: Ni3P2
B: Ni2(PO3)3
C: NiPO4
D: NiHPO4
E: Ni3(PO4)2
Question 29
Consider the molecular orbital diagrams of two molecular species A and B and their ions:
B
A2+
A
B2+
Select the correct statement:
A.
B.
C.
D.
E.
When A and B2+ are brought together a spontaneous redox reaction occurs.
B is a better oxidizing agent than A2+.
A is able to reduce B.
All of the above
None of the above
Question 30
(C5H8)
A. This molecule is polar, a fairly good Brønsted acid and all carbons have sp2 hybridization.
B. This molecule is non-polar, neither base nor acid and one of the carbons has sp3
hybridization.
C. This molecule is polar, a fairly good Arrhenius base and one of the carbons has sp3
hybridization.
D. This molecule is polar, a good Lewis base and all carbons have sp3 hybridization.
E. This molecule is non-polar, neither base nor acid and all carbons have sp2 hybridization.
Question 31
Consider the following energy diagram for a reaction without catalyst (solid line) and with a catalyst
(dashed line)
E in kJ/mol
B
+2
D
Energy
-2
C
-3
-18
E
A
A.
B.
C.
D.
E.
-23
The catalyst lowers the activation energy for the AE reaction by 4 kJ/mole
In the presence of the catalyst the species C will no longer be present in small concentrations
The enthalpy of reaction AE is -5 kJ/mole
All of the above
None of the above
Question 32
Blue LED’s are made from the semiconductor GaN that possesses a
zinc blende type structure. These LED’s emit photons with a
wavelength of 403 nm.
Avogadro’s number= 6.02214×10+23 [mol-1]; the speed of light =
3.00×10+08 [m/s]; Planck’s constant= 6.626,068,96×10-34 [Js];
E=hν; νλ=c
Select the correct statement
A.
B.
C.
D.
E.
One mole of blue photons from this source contains 297 kJ of energy
The coordination number is 4 for both gallium and nitrogen
The material is called gallium nitrite
Both A and B are correct
All above statements are correct
Question 33
How many moles of FeCl3 are formed when 5 mol Fe and 6 mol of Cl2 are allowed to react. (Hint: First
write a balanced equation)
a)
b)
c)
d)
e)
4 mole
5 mole
7.5 mole
3 mole
6 mole
Question 34
Consider the Bohr model for a hydrogen atom.
(
)
Which of the following changes of the principle quantum number emits a photon with the highest
energy?
A.
B.
C.
D.
E.
From n=2 to n=3
From n=1 to n=6
From n=2 to n= 1
From n=3 to n= 2
From n=6 to n=1
Question 35
Amy has the following five aqueous solutions:
1.
2.
3.
4.
5.
0.01 M H2SO4
0.01 M NH4Cl
0.01 M NaCl
0.01 M CH3COONa (sodium acetate)
0.01 M HCl
She measures the pH for each of them with an electrochemical pH-meter. She will find the following
order:
A.
B.
C.
D.
E.
pH(1)<pH(5)<pH(2)<pH(3)<pH(4)
pH(4)<pH(3)<pH(2)<pH(5)<pH(1)
pH(2)<pH(1)<pH(4)<pH(3)<pH(5)
pH(1)<pH(2)<pH(3)<pH(4)<pH(5)
pH(3)<pH(2)<pH(1)<pH(4)<pH(5)
pKa (acetic acid)= 4.9; pKa(NH4+)=9.5
Question 36
Although the Bohr model accurately described the observed absorption and emission spectra of the
hydrogen atom, the theory was replaced by quantum theory, because:
a)
b)
c)
d)
e)
It was found that in vacuum the electron could actually adopt a continuum of energy states
It failed to describe even simple ions with only one electron, like He+ or Li2+
It did not explain why the electron did not simply fall back all the way to the nucleus
All of the above
None of the above.
Question 37
P
Caprica
Alduran
250
280
310
340
T
The above diagram represents the (P-T) phase diagram for water. Temperatures are in Kelvin. On two
planets in the delta quadrant of our galaxy, Caprica and Alduran, conditions are a bit different than on
earth. The mean atmospheric pressures for the two planets are indicated by horizontal lines. All
observations are done in outdoors conditions. Select the correct statement
On Alduran ice does not melt at all, instead it sublimes at about -20oC.
On Caprica ice melts at about 10oC, but it boils at 100oC like on earth.
The atmospheric pressure on both planets is higher than that of earth
On both planets the melting point of ice is observed at the same temperature as on earth
because melting points do not change much with pressure
E. None of the above is true
A.
B.
C.
D.
Question 38
Compare the electron configurations of a zirconium and a tin atom. Both atoms possess 4d electrons.
Select the correct statement
A. In the transition series between the two elements the effective nuclear charges are decreasing,
such that the tin 4d electrons have become valence electrons.
B. The tin 4d electrons are core electrons and therefore tin always adopts a 2+ oxidation state,
whereas zirconium tends to be either 1+ or 4+.
C. The increase in nuclear charge from zirconium to tin makes the ten 4d electrons core levels for
tin, but both elements can form 4+ oxidation states.
D. Both tin and zirconium have 4d2, but due to the difference in shielding the tin electrons are
considered valence electrons; for zirconium they are not.
E. None of the above.
Question 39
H
H
H
N
C
N
C
F
H
H
Consider the above molecule and select the correct statement
A.
B.
C.
D.
E.
The angle H-N=C (on the left) is 120 degrees.
Both carbon atoms can be described with sp2 hybridization.
Only the one fluorine atom possesses lone pairs, not shown in the figure.
All of the above
None of the above.
Question 40
Consider the molecules CO2, BF3 and NH3
A. NH3 is a moderately strong Lewis base because it has a lone pair
B. CO2 and BF3 are Lewis acids because the central atom has less than four electron regions around
it
C. Neither CO2 nor BF3 has a permanent dipole, but NH3 does
D. All of the above
E. None of the above
Questions 41-50
True or False:
41. The entropy of the universe is in the process of decreasing
42. In the calculation of Lewis structures we assume that electrons are all paired and either localized on
one atoms or shared by only two
43. The angular momentum quantum number l can have n different values for a given value of n
44. The principle of Le Châtelier says that an equilibrium, when exposed to an outside stress, will strive
to undo the stress by shifting
45. Electronegativity is simply the fact that electrons are negative rather than positive particles.
46. The concept of hybridization says that ions like Fe2+ can act both as oxidizing and as reducing agents.
47. The molecule SF6 has an octahedral shape and cannot be described by assuming sp3 hybrids
48. The activity of a solution of arsenate with [AsO43-] = 0.0001 [mol/lit] is simply a dimensionless
0.0001 because we divide by the standard concentration of 1 [mol/lit]
49. When a chemical reaction between two liquids produces a gas the entropy is increasing.
50. Gallium melts around body temperature (37oC). At this temperature it would dissolve more easily in
acetone (CH3-C=O-CH3) than in mercury.