Download “Midterm” Exam # 1 - Elgin Community College

CHM142
Elgin Community College
Final Exam
Dr. Trail
total = 150 points
Name KEY
Use only the space provided and show all your calculations. If you can’t do the first part of a problem, then
make up a number and use that for the rest of the problem. Best of luck! 14.7 psi = 1 atm = 760 mm Hg,
Avogadro’s number 6.02x1023, R = 0.082 L*atm*K-1*mol-1, R = 8.314 J*K-1*mol-1
1) (4 pts) Name the following substances:
NaHCO3 Sodium bicarbonate
H2SO4
Ta3N5
HClO4
tantalum (V) nitride
sulfuric acid
perchloric acid
2) (4 pts) Write the chemical formulas for the following substances:
sodium sulfate
Na2SO4
diphosphorus pentoxide P2O5
ammonia
ammonia
iron (II) carbonate FeCO3
3) (4 pts) The number of protons in the nucleus of a specific atom is equal to its
a. atomic weight
b. mass number
c. atomic number
d. mass number minus the atomic number
4) (4 pts) The most stable ion of chlorine is isoelectronic with the
a. magnesium ion
b. fluorine ion
c. argon atom
d. sodium ion
5) (4 pts) The energy of a photon is greatest in the case of
a. x-radiation
b. ultraviolet radiation
c. visible light
d. infrared radiation
6) (4 pts) Which ion has twenty-six electrons?
a. Cr2+
2+
b. Fe
(c) Ni2+
(d) Cu2+
CHM142
Elgin Community College
Dr. Trail
(4 pts) List the sources of Energy in the United States from 1 being the most used to 7 being the
least used – don’t worry, I won’t be too picky about the order )
___3__ Nuclear Power
___6__ Wind power
___2__ Natural Gas
___2__ Coal (very close to natural gas)
___4__ Hydroelectric (water power from dams)
___7__ Solar
__1___ Petroleum
(4 Biomass is tied with hydroelectric)
(5 geothermal)
7) (2 pts) Most of Illinois’s electricity is obtained from: Nuclear
8) (6 pts) Please fill in the following Table
°F
°C
°K
Boiling point H2O
212
100
373
Freezing Point H2O
32
0
273
Absolute Zero
(coldest possible
Temperature)
-459
-273
0
9) (4 pts) I have listed several temperatures below – CIRCLE the temperatures that are reasonable – CROSS
OUT the bogus ones (one is right and one is wrong for each example) (the temperatures are approximate
so if within a few degrees or so, it’s o.k.)
180°C or
363°K
Temperature to bake cookies
-70°F or
0°F
or
68°C or
-70°C
0°K
19°C
which is colder?
absolute zero
Room temperature
180°C is good – 373K bogus – lower than
boiling point of water
-70C is colder (it equals -94F)
0°K good, 0°F is much, much warmer
19C is fine, 68C is scorching
10) (4 pts) Predict which element would have the largest difference between its third and fourth
ionization potentials.
(a) Sodium
(b) Silicon
(c) Aluminum
(d) Magnesium
11) (4 pts) In all +1 ions, there is
a) one more proton than neutrons
c) one more electron than and protons
e) one more positron than electrons
b) there is one more neutron than protons
d) one more proton than electrons
f) one more electron than positrons
12) (4 pts) Gallium, in gallium(I) nitride, has the following electronic configuration
(a) 4s23d104p1
(d) 3d10
(b) 4s23d10
(e) 5s25p3
(c) 4s24d104p1
(f) 4s24d10
CHM142
Elgin Community College
Dr. Trail
13) (12 pts) Write Please convert the following and watch significant figures:, 454 g = 1 lb;
1.0 kg = 2.2 lb; 16 oz = 1 lb;
7.5 g =
__________ oz
7.5g ( 1 lb )(16 oz) = 0.26 oz
(453.6g) (1 lb)
1.25 km =
__________ cm
1.25 km (103 m)(102 cm) = 1.25x105cm
(1 km) (1 m)
12 L*atm =
__________ J (hint – use the two R’s)
0.08206 L*atm = 8.314 J
K*mol
K*mol
solve for Joules
J = 101.3 L*atm
0.30nm x 0.20nm x 1.0nm = __________ mL
0.60nm3 ( 1 m )3 (102 cm)3 = 0.60 x 106 = 0.60 x 10-21 cm3 or 6.0x10-22 mL
(109 nm)3 (1 m)
1027
14) (4 pts) In atomic absorption spectroscopy,
(a) a photon is emitted causing an electron to fall from one atomic energy level to another
(b) a photon is absorbed causing an electron to fall from one atomic energy level to another
(c) a photon is emitted causing an electron to rise from one atomic energy level to another
(d) a photon is absorbed causing an electron to rise from one atomic energy
level to another
(e) an electron is emitted causing a photon to rise from one atomic energy level to another
15) (4 pts) An atom has a valence shell electron configuration of ns2np5. To which group of elements
in the periodic table does it belong?
(a) Transition metals
(d) Alkaline earth metals
(b) Rare earth metals
(e) Alkali metals
(c) Chalcogens
(f) Halogens
16) (4 pts) What is the oxidation number of phosphorus in H 3PO3?
(a) +1
(b) +2
(c) +3
(d) +4
17) (4 pts) The methane molecule, NH3, has a structure best described by the term
(a) pyramidal
(d) triangular
(b) trigonal pyramidal
(e) trigonal bipyramidal
(c) orthorhombic
(f) rhombohedral
CHM142
Elgin Community College
Dr. Trail
18) (4 pts) When dilute aqueous solutions of lead (II) nitrate and potassium bromide are mixed, a precipitate is
observed. The products of this reaction are:
(a) Pb2+(aq) + Br−(aq) + KNO3(s)
(b) Br2(aq) + NO2(g) + PbK2(s)
(c) PbO(s) + K+(aq) + Br−(aq) + NO2(g)
(d) PbBr2(s) + K+(aq) + NO3−(aq)
19) (4 pts) When the following system is balanced H2O + Cl− → ClO2− + H+ + e−
How many electrons are needed to balance the equation?
Cl–
+ 2H2O
→
ClO2–
+ 4 H+
+ 4 e–
(done with half reaction method)
You could also look at the redox states
Cl–
is Cl in the -1 oxidation state
ClO2– is Cl in the +3 oxidation state
To go from -1 to +3 you need to remove 4 electrons (so the product is 4 e–)
20) (4 pts) What do all parts of this symbol mean?
3 mass number = protons + neutrons
1 atomic number = # protons
+1 charge of the ion
What is T ? tritium – the isotope of hydrogen with 2 neutrons
21) (4 pts) Calculate the mass of:
100 H atoms ( 1 mole H atoms )(1 g H) =
(6.02x1023 H atoms)(1 mol H)
(WORK MUST BE SHOWN FOR CREDIT)
2x10– 22 grams of H
22) (6 pts) Atomic Structure
Rank the following masses (1 being the heaviest)
electron
3
proton
2
Draw a picture of a helium atom including all of it’s “parts” Include charges.
neutron
1
CHM142
Elgin Community College
23) (4 pts) Balance this reaction
Dr. Trail
1 H2SnCl6 + 2 H2S  1 SnS2 + 6 HCl
24) (4 pts) Calculate the pressure exerted by 54 g of steam (H 2O) confined to a volume of 18 L at
100.°C.
PV = nRT
P=nRT/V = (3.0)(0.08206)(373)/18 = 5.1 atm
n = 54 g (1 mol/18g) = 3.0 moles
T = 100. + 273 = 373K
25) (4 pts) In the Periodic Table Outline below, please label.
a) Lanthanides (Rare Earth Metals)
b) Alkaline earth metals
c) Actinides (Transuranic elements)
d) Alkali metals
e) Halogens
f) Noble Gases
g) Pnictides
h) Chalcogenides
i) Transition Metals
26) Consider the following ion: ICl2+
# valence electrons: 21-1 = 20 electrons
Draw the Lewis Dot Structure
Predict the shape of the ion BENT and draw it:
Do you expect it to be polar?
Yes
What hybridization does each atom have?
All three atoms are sp3 hybridized
Discuss the bonding
A sigma bond between each Cl and I that is sp3 hybridized. 3 lone pairs on each Cl and two lone pairs
on I
CHM142
Elgin Community College
Dr. Trail
27) Consider the following molecule: HArF
# valence electrons: 1 + 8 + 7 = 16e
Draw the Lewis Dot Structure
Predict the shape of the ion linear and draw it
Do you expect it to be polar? Yes
What hybridization does each atom have?
H 1s orbital only
Ar dsp3
F sp3
Draw all of the hybrid orbitals
28) (4 pts) What is the mass of one atom of
carbon 12 (12C) in grams?
a)
b)
c)
d)
e)
12.0 g
12.0000000 g (infinite sig. figs)
6.0 g
-23
1.99 x 10
g
–22
1.06 x 10
g
29) (6 pts) If 2 g of sugar is burned to heat 1.5 L of water, how much will the temperature rise if the
starting temperature is 20.°C? calories = m*C* ΔT
Sugar contains 4 Calories per gram.
(typo – should have been
Cal not cal)
2 g sugar (4 Cal) = 8 Cal or 8000 cal
1.5 L = 1500 mL = 1500 grams for water (density = 1g /mL)
(g)
q =mCs ΔT or ΔT = q
= 8000
= 5.3° = T2-T1
T2 = 5.3 + 20 = 25.3°C
mCs
(1500*1)
30) (2.5 pts) Please determine the number of significant figures in each of the following numbers:
NUMBER
NUMBER OF SIGNIFICANT FIGURES
1000.0
5
322.220
6
−555
1.230*10
4
0.0123
3
100
1
CHM142
Elgin Community College
Dr. Trail
31) (4 pts) A student measures the pH of distilled water by titrating with a burette and with an
electronic pH meter. He/She obtains the following data:
Burette:
pH Meter
7.10
7.01
6.90
7.15
6.85
6.500
6.502
6.499
6.502
6.500.................................................(circle the best answer)
The Burette (in the hands of a student):
accurate
precise
accurate and precise
(i.e. the student’s inexperience is the cause of the imprecision, not the burette)
Accurate since the average is close to 7.00 which is the pH of neutral water
The pH Meter is:
accurate
precise
accurate and precise
Very repeatable (small error between measurements) but systematically off by a lot: 5 parts out
of 65 or 7% even thought it reports four sig figs)
32) (4 pts) In the reaction S8 + 8O2(g)
0
0
8SO2(g)
Assign oxidation states to each atom
+4 -2
Which atom is being oxidized? Sulfur
Which atom is being reduced? Oxygen
33)
(4 pts) As a bicycle tire is inflated with 125 Joules of work, the surroundings absorb 180 Joules of
heat. The change in the internal energy is:
w = +125 Joules as work is done TO the tire
q = -180 Joules heat since heat LEAVES the system
ΔE = q+w = 125-180 = -55 Joules
34)
(4 pts) The planet Mars has an atmosphere composed of 95.2% CO2 2.7% N2 and 1.6% Ar. Assume
the remaining gas is CO. The total pressure on Mars is 0.477 Torr. Calculate the pressures, in Torr of all four
gases and the mole fraction
%
Torr
Mole Fraction
CO2
95.2
0.454
0.952
N2
2.7
0.013
0.027
Ar
1.6
0.0076
0.016
CO
0.5
0.002
0.005
Pa = XaPtot
CHM142
Elgin Community College
Dr. Trail
35) (6 pts) If you have 200 g of CaCl2, how many grams of a 20.% (m/m) solution can your prepare? How
much water do you need to use (mL)? Show ALL of your work for credit
20% (m/m)
20. g CaCl2
100 g soln
and 200 g CaCl2
flip over the conversion factor and mult
200x(100/20) = 1000 g soln
Then, solution = solvent + solute or 1000 g = x + 200g so 800 g H2O needed or 800
mL since the density of water is 1.00 at room temperature.
36) (6 pts)
What is the molecule with this molecular orbital diagram? O2
What is the bond order ? (8-4)/2=2
Is it paramagnetic or diamagnetic?
E=h
E=mc2
c=
paramagnetic
Kinetic Energy = 1/2mv2
(6 pts) Derive deBroglie’s relationship for the wavelength of matter
Combine E=h
Set
c=
E=hc/ equal to
or (6-2)/2 = 2
= ? remember to convert c to v
and get E=hc/
E=mc2
and hc/
= mc2
solve for
= h/(mc)
Since matter can’t travel at the speed of light, change c to v for velocity
= h/(mv)