Download CHEM 2: Exam 3

CHEM 2: Exam 3
Name:___________________________________________________________________ Points: _____ / 100
Please read each question carefully. Where the question specifies “MARK ALL THAT APPLY”, you may
need to select more than one answer on the scantron.
1.
Provided the unit conversions below, convert 40.3 pounds per square inch (psi) to kilopascals (kPa).
Unit Conversions:
A.
B.
C.
D.
E.
14.7 psi = 1 atm
760 mmHg = 1 atm
760 mmHg = 101.325 kPa
2.74 kPa
278 kPa
5.84 kPa
592 kPa
These units cannot be interconverted.
2.
Imagine a car tire is filled to a pressure of 32 psi when it’s cold at 13 oC. Assuming a constant volume, how would the pressure
inside the tire change as the tire heats up with driving?
A. The pressure in the tires would increase.
B. The pressure in the tires would decrease.
C. The pressure in the tires would remain the same.
D. It depends: the exact final temperature would have to be specified.
3.
A cylinder initially contains 10.0 L of a gas at 90 psi & 300 K. How would the pressure change if the gas was heated and the
volume of the cylinder increased?
A. The pressure in the cylinder would increase.
B. The pressure in the cylinder would decrease.
C. The pressure in the cylinder would remain the same.
D. It depends: the exact final temperature and volume would have to be specified.
4.
Imagine you are a scuba diver at a depth of 20 meters below the water surface where the pressure is 3 atm. If you fill your
lungs to a total capacity of 6 Liters at this depth and hold your breath, then rise to the surface where the pressure is 1 atm,
what would be the final volume of the air in your lungs? Assume the temperature is constant.
A. 2 L
B. 3 L
C. 6 L
D. 12 L
E. 18 L
5.
A balloon with an initial volume of 1.2 L at a temperature of 18 oC is warmed to 350. K. Assuming a constant pressure, what
is the volume of the balloon at the final temperature?
A. 0.32 L
B. 1.4 L
C. 5.1 L
D. 23 L
E. None of the above
6.
A bag of potato chips contains 585 mL of air at 25 oC and a pressure of 765 mmHg. Assuming the bag does not break, what
will be its volume at the top of a mountain where the pressure is 442 mmHg and the temperature is 5.0 oC?
A. 4.9 mL
B. 203 mL
C. 945 mL
D. 2700 mL
E. None of the above
7.
A sample of an ideal gas has a volume of 11.2 L with a pressure of 1 atm and a temperature of 546 K. Approximately how
many moles of gas are present in this sample?
A. 0.25 mole
B. 0.5 mole
C. 0.75 mole
D. 1 mole
E. Not enough information provided: The identity of
the gas would have to be specified.
CHEM 2: Exam 3
8.
A sample of an ideal gas contains 2 moles of gas at a pressure of 380 mmHg and a temperature of 136.5 K. What is the
approximate volume of this gas sample?
A. 11.2 L
B. 22.4 L
C. 33.6 L
D. 44.8 L
E. 89.6 L
9.
2 moles of nitrogen dioxide gas (NO2(g)) are initially confined to a container with a constant volume of 10 L and a constant
temperature of 298 K. If all of the NO2(g) reacts according to the reaction below, how would the pressure within the
container change?
2 NO2(g) → 1 N2O4(g)
A. The pressure in the container would increase.
B. The pressure in the container would decrease.
C. The pressure in the container would remain constant.
D. Not enough information is provided: initial pressure would have to be specified.
10. Which sample of gas below would have the largest volume? Assume all samples are at the same temperature and pressure.
A. 1.1 mole of Helium (He)
B. 1 mole of Argon (Ar)
C. 0.5 mole of Cl2
D. 0.5 mole of CH3CH2CH2CH3
E. 0.25 mole of I2
11. If 0.500 moles of sodium azide (NaN3(s)) completely decomposed according to the reaction below, what volume of nitrogen
gas would be obtained at Standard Temperature and Pressure (STP)?
2 NaN3(s) → 2 Na(s) + 3 N2(g)
A.
B.
C.
D.
E.
11.2 L
16.8 L
33.6 L
44.8 L
67.2 L
12. What volume of butane gas (C4H10(g)) would be needed to fully react with 2.6 L of oxygen gas according to the combustion
reaction below?
2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
A. 200 mL
B. 400 mL
C. 2.6 L
D. 5.2 L
E. 16.9 L
13. Identify ALL of the intermolecular forces present in the covalent substance diborane with the formula B 2H6. MARK ALL
THAT APPLY.
A. London Dispersion Forces
B. Dipole-Dipole Forces
C. Hydrogen Bonding
D. Inter-ionic Forces
E. Not enough information is provided: the Lewis dot structure and connections between the atoms would have to be
provided.
14. Identify ALL of the intermolecular forces present in the gas carbon monoxide. MARK ALL THAT APPLY.
A. London Dispersion Forces
B. Dipole-Dipole Forces
C. Hydrogen Bonding
D. Inter-ionic Forces
E. Not enough information is provided.
CHEM 2: Exam 3
15. Identify the strongest intermolecular force present in the covalent substance hydrazine with the formula N 2H4.
A. London Dispersion Forces
B. Dipole-Dipole Forces
C. Hydrogen Bonding
D. Inter-ionic Forces
E. Not enough information is provided: the Lewis dot structure and connections between the atoms would have to be
provided.
16. A cylinder contains equal amounts of the 4 gases below. If the temperature of the cylinder was gradually decreased, which
gas would be the first to condense to form a liquid?
A. CH4
B. CH3CH3
C. NH3
D. B2H6
E. None of the above: they will all stay as gases even as the temperature decreases.
17. Of the 4 substances below, which would have the highest solubility in water?
A. CH4
B. C6H14
C. CH3OH
D. N2
E. Not enough information is provided: the Lewis dot structure and connections between the atoms would have to be
provided.
18. Of the 5 substances below, which would have the highest melting point?
A. C6H14
B. CH3OH
C. H2O
D. MgO
E. Xe
19. Of the 5 substances below, which would have the lowest melting point?
A. CH4
B. CH3CH3
C. CO2
D. NH3
E. Li2O
20. The viscosity of a liquid can be qualitatively thought of as the thickness of the liquid. Which substance below would have
the highest viscosity? Assume each substance is at the same temperature.
A. Br2
B. C5H12
C. C10H22
D. C20H42
E. H2Se
FREE RESPONSE QUESTIONS: Show your work, and partial credit will be awarded where possible.
1.
How many electrons would be included in the Lewis dot structure of NO+?________________
2.
How many electrons would be included in the Lewis dot structure of PO43-?_________________
3.
Arrange these diatomic molecules in order of DECRASING polarity: HF, NO, F2, CO.
HIGHEST Polarity: ____________<____________<____________<____________: LOWEST Polarity
CHEM 2: Exam 3
4.
Which substance below is most likely a liquid at room temperature? EXPLAIN your reasoning using concepts from polarity
and intermolecular forces.
CO2
CS2
5.
Which substance below is most likely a liquid at room temperature? EXPLAIN your reasoning using concepts from polarity
and intermolecular forces.
6.
Rank the molecules below from LOWEST water solubility to HIGHEST water solubility. EXPLAIN your reasoning by describing
the types of intermolecular forces present in each substance and how this affects the molecular polarity & in turn affects
the water solubility.
HOCH2CH2OH
CS2
CH2Cl2
LOWEST Water Solubility: ____________<____________<____________:HIGHEST Water Solubility
CHEM 2: Exam 3
7.
Some theories on aging suggest that free radicals cause a variety of diseases and aging. Free radicals are molecules or ions
that contain an UNPAIRED electron. Free radicals react quickly and attack molecules within the cell, such as DNA, changing
them and causing cancer or other diseases.
Circle ALL of the molecules or ions below that would LIKELY exist as free radicals. Use concepts and terms from Lewis theory
to EXPLAIN why these sorts of molecules are so HIGHLY REACTIVE.
S8
O2-
HF
OH
CH3O2
8.
Draw the Lewis dot structure for the polyatomic ANION phosphite, PO33-.
9.
What is the approximate O—C—Cl bond angle in OCCl2? Explain your choice by describing the molecular shape at the central
Carbon atom.
10. Calculate the molar mass of a gas if it has a density of 5.93 g/L at a pressure of 760.0 mmHg and a temperature of 25.0 oC.
Hint: First find the number of moles of gas if a sample has a mass of 5.93 g and a volume of 1 L.
CHEM 2: Exam 3
EXTRA CREDIT: 5 points
3 Liters of Nitrogen gas combines with 6 liters of hydrogen gas to produce 3 liters of a gaseous compound containing only nitrogen
and hydrogen (NxHy). What is the empirical formula of the gaseous product that is produce? Explain your answer using Avogadro’s
Law and by writing the balanced chemical equation.
REFERENCE INFORMATION:
𝑫𝒆𝒏𝒔𝒊𝒕𝒚 =
𝑀𝑎𝑠𝑠
𝑉𝑜𝑙𝑢𝑚𝑒
P1V1 = P2V2
P1/T1 = P2/T2 V1/T1 = V2/T2 V1/n1 = V2/n2
PV=nRT, where R = 0.08206 L·atm/mol·K = 62.37 L·torr/mol·K = 8.314 L·kPa/mol·K
Temperature Conversion: Kelvin = oC + 273.15
Pressure Conversions: 1 atm = 14.7 psi = 760 mmHg = 101.325 kPa = 760 torr
At STP: Pressure = 1 atm, Temperature = 273 K & 1 mole of gas = 22.4 L
CHEM 2: Exam 3