Problem Set 19
Midterm Review Problems II 2012
A. Chemical Reactions
. 1. Write and balance the reaction between the following:
a. copper and zinc chloride
Cu + ZnCl2  Cu Cl2 + Zn
Or 2Cu + ZnCl2  2Cu Cl + Zn
because Cu has >1 oxidation state
b. magnesium sulfate and potassium fluoride
MgSO4 + 2KF  MgF2 + K2SO4
B. Atomic and electron structure
2. Tell me all you can about a fictional element with an atomic number of 145 and an
atomic mass of 320.
145 protons, 145 electrons, 320-145 = 175 neutrons, not discovered yet
3. Compare and contrast the Bohr and Electron cloud models of the atom
Bohr
Electron Cloud
both
Electrons have location
e- have prob. Only
energy levels
Orbits
orbitals (spdf)
valence same
Protons, neutrons
nucleus
4. What is the electron configuration of selenium?
[Ar] 3d104s24p4
5. What element has an electron structure of 1s22s22p63s23p64s23d104p65s24d105p5 ?
Iodine
C. Stoichiometry
6. If one starts with 62.3g of aluminum oxide and excess hydrochloric acid how many
grams of aluminum chloride is made?
Al2O3 + 6HCl  2AlCl3 + 2H2O
Al2O3
62.3 g
1 mole
2
133.33 g
101.96 g
1
1 mole
= 62.3 g AlCl3
7. In the reaction between hydrochloric acid and zinc, if 12.78 g of hydrochloric acid and
58.0 g of zinc are used, which is the limiting reactant? How much of the excess reactant
will be left?
2HCl + Zn  ZnCl2 + H2
1.
HCl
12.78 g
1 mole
36.45 g
1
2
2.00g = .3506 g
1 mole
2. Zn
58.og
1 mole
1
2.00 g = 1.77 g
65.39 g
1
1mole
Clearly, HCl is limiting because it makes less product.
How many mole of HCl are used?
12.78 g
1 mole 1
36.45 g
2 = 0.17 mole
So 0.17 moles of Zn are also used
0.17 moles 65.39 g = 11.11 g
1mole
Left over zinc: 58.0 g – 11.11g = 46.89 g
D. Atomic Theorists
Match each theorist with the model
1.
2.
3.
4.
5.
6.
7.
Thomson
Aristotle
Dalton
Democritus
Bohr
Schrodinger
Heisenberg
A.
B.
C.
D.
E.
F.
electron cloud
earth, air, fire and water
atmos
billiard ball
planetary
plum pudding
F. Atomic Theorists
Match each theorist with the model
1.
2.
3.
4.
5.
6.
7.
8.
Thomson
Aristotle
Dalton
Democritus
Bohr
Schrodinger
Heisenberg
A.
B.
C.
D.
E.
F.
electron cloud
earth, air, fire and water
atmos
billiard ball
planetary
plum pudding
What if?
1.
What if all of the particles that Rutherford sent through the foil went straight
through? What would this mean about the atom?
The Thomson model of the atom was correct: the atom was made of a diffuse
positive charge with small imbedded electrons.
2. What if Dalton found that atoms combined in fractions? What would this mean
about the atom?
This would be interesting: atoms could not be the smallest unit of an element!
3. What if Bohr discovered that electrons did indeed plummet into the nucleus?
What would this mean about the atom?
The atom would not be sustainable: atoms would self destruct. This would mean
there was no matter and that we did not exist.
4. What if Heisenberg found that one COULD predict the speed and location of an
electron? What would this mean about the atom?
That the probability model was incorrect: we could know and assign locations to
all electrons.
Compare and contrast
1.
An ion and an isotope
Ion is varied number of electons with the protons the same and is charged.
Isotope is varied number of neutrons with protons the same: no charge but
mass changes
2. Dalton’s and Democritus’ models of the atom
Both were solid spheres that were indivisible. Dalton’s was based on
experiment, Democritus on speculation
3. The planetary and plum pudding models of the atom
The Rutherford/Bohr model (planetary) says the atom is mostly space with a
positive dense nucleus. The Thomson (plum pudding) model says that atoms
are mostly a positive matrix with negative particles. Thomson had no idea
about the nucleus.
E. Percent Composition
1. What is the percent of each element in:
a. NH4OH
N
14 /35 x 100%
H
5/35 x 100% =
O
16/35 x 100% =
=
b. AgNO3
Ag 107.8 / 169.8 x 100% +
N 14/169.8 x 100% =
O 16 x 3 =48/169.8 x 100% =
F. Predicting Products
a. Ca(OH)2 + 2 KI  2 KOH + CaI2
b. 2 Na + Au(NO3)2  2 NaNO3 + Au
c. 2 Mg + O2  2 MgO
d. 2 C2H6 + 7 O2  4 CO2 + 6 H2O