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Quiz Session - Attempts With Random Questions

College Chemistry Exam Questions

Page 5 of 25

81.

In a crystalline solid, what is the coordination number?

  • The number of atoms adjacent to any one atom in the crystal lattice

  • The number of atoms per unit cell in the crystal lattice

  • The amount of energy required for a peripheral molecule to sublime

  • The amount of energy released by a new molecule getting added to the lattice

  • The average distance between two nuclei in the lattice

Correct answer: The number of atoms adjacent to any one atom in the crystal lattice

For example, a simple cubic structure has a coordination number of 6 while a hexagonal, closely-packed structure has a coordination number of 12.

82.

The following equation relates the equilibrium constant, K, to Gibbs Free Energy:

ΔG = -RTln(K)

Under which condition do you expect a reaction to be spontaneous?

  • K > 1

  • K < 1

  • K < 0

  • K > 0

  • K >> 0 

Correct answer: K > 1

ln(1) = 0, and the natural log of any number >1 is positive. Since we know that R is a positive constant and T will always be positive (units are in Kelvin, so 0 is absolute zero), the ln(K) term determines the sign of ΔG. If ln(K) is positive, then ΔG will be negative and therefore spontaneous. This should make intuitive sense because K > 1 represents the predominance of products over reactants.

83.

If the following reaction were powering a Voltaic cell, which half-reaction is occurring at the cathode?

2AgNO3 (aq) + Cu (s) ⇋ Cu2+ (aq) + 2Ag (s)

  • 2Ag+ (aq) + 2e- ⇋ 2Ag (s)

  • 2AgNO3 (aq) + 2e- ⇋ 2Ag (s) + 2NO3- + 2e-

  • Cu (s) ⇋ Cu2+ (aq) + 2e-

  • Cu (s) ⇋ Cu2+ (aq) + 2NO3- + 2e-

  • 2AgNO3 (aq) + 2e- + Cu (s) ⇋ Cu2+ (aq) + 2Ag (s) + 2NO3- + 2e-

Correct answer: 2Ag+ (aq) + 2e- ⇋ 2Ag (s) 

The cathode is the site of reduction, or electron gain, so you should expect electrons to be included in the reactants. NO3- is excluded because it is a spectator ion, remaining in solution while not participating in the reduction itself.

84.

If you are working with gases in equilibrium, what entity should you use to calculate the equilibrium constant K or reaction quotient Q?

  • Partial pressures

  • Concentrations (in molarity)

  • Molecules (in moles)

  • Mole fractions

  • Kinetic energy

Correct answer: Partial pressures

Just as molar concentrations can be used to calculate equilibria in solution, partial pressures can be used for gaseous equilibria.

85.

In PCl5, what is the percent composition of phosphorous?

  • 14.9%

  • 16.7%

  • 20%

  • 33.3%

  • 29.8%

Correct answer: 14.9%

"Percent composition" refers to the percentage of molecular mass that each element accounts for. Molar masses are P = 30.98 and Cl = 35.45, so total molecular mass is 30.98 + (5*35.45) = 208.24, and P accounts for 30.98/208.24 = 14.9% of that mass.

86.

All other conditions held equal, which of the following changes would reduce the viscosity of a liquid?

  • Increased temperature

  • Decreased temperature

  • Increased pressure

  • Decreased volume

  • Increased volume

Correct answer: Increased temperature

Viscosity (resistance to flow) relates to the intermolecular forces in a liquid: the more the molecules are attracted to each other, the less they are willing to flow. At higher temperatures, molecules move faster and have less time to interact with each other. The intermolecular forces are, therefore, weakened, and the liquid flows more readily.

87.

What does it mean for an atom to be reduced?

  • It gains an electron

  • It loses an electron

  • Its atomic radius contracts

  • It loses a neutron

  • It loses a proton

Correct answer: It gains an electron

Oxidation involves the loss of an electron, while reduction involves the gain of an electron. If you find this hard to remember, think OIL RIG: "Oxidation Is Loss, Reduction Is Gain." If reduction is occurring, then oxidation too must be occurring to a different atom/compound.

88.

What is the defining characteristic of an adiabatic system?

  • No heat is exchanged between the system and its surroundings

  • No work is done by the system on its surroundings

  • The system has constant temperature

  • The system has constant pressure

  • The system has constant volume

Correct answer: No heat is exchanged between the system and its surroundings

A system's internal energy is comprised of heat and work, so an adiabatic system is useful because any change in internal energy must be due to work done on/by the system. In actuality, it is very difficult to create a truly adiabatic system. However, some processes such as compression of a gas in a cylinder occur so quickly that there isn't time for heat to be exchanged, and the process can be approximated as adiabatic.

89.

What kind of reagent do you need to make the following change occur?

SO42-  S2-

  • Reducing agent

  • Oxidizing agent

  • Acid

  • Base

  • Precipitating agent

Correct answer: Reducing agent

Consider the oxidation states involved: S is +6 on the left and -2 on the right, so it gets reduced. A "reducing agent" is needed to accomplish this electron transfer.

90.

Alcohols and ethers both contain oxygen. What is the structural difference?

  • An alcohol is a terminal -OH; an ether is an O bonded to two C atoms

  • An alcohol is a terminal -OH; an ether is an O adjacent to a C=O double bond

  • An alcohol is an O bonded to two C atoms; an ether is a terminal -OH

  • An alcohol is an O bonded to two C atoms; an ether contains O in a 5- or 6-membered ring

  • An alcohol occurs off a 5- or 6-membered ring; an ether can occur anywhere

Correct answer: An alcohol is a terminal -OH; an ether is an O bonded to two C atoms

This difference gives alcohols and ethers very different reactivities. Do not mix ethers up with esters, which contain an O-C single bond that is adjacent to a C=O double bond.

91.

Two molecules with the same chemical formula but different configurations of atoms/bonds are called:

  • Isomers

  • Isotopes

  • Allotopes

  • Diastereomers

  • Amphitypes

Correct answer: Isomers

Two isomers may differ from each other in atomic configuration, associated ions, molecular geometry, and more. Sometimes, isomers will have very similar properties, but often they do not.

Diastereomers are a specific type of isomer often discussed in organic chemistry. (Isotopes are atoms with the same number of protons but different numbers of electrons. Allotopes and Amphitypes do not exist.)

92.

Which of the following sets of conditions indicates that a reaction is at equilibrium?

i. K = Q

ii. Q = 0

iii. K = 1

iv. ΔG = 0

  • i. and iv.

  • iv. only

  • i. only

  • ii. and iv.

  • iii. and iv.

Correct answer: i. and iv.

The equilibrium constant K may range from 0 to infinity, depending on the equilibrium ratio of products and reactants. The reaction is at equilibrium only when the reaction quotient Q reflects the balance of products and reactants in K. When Q=K, ΔG goes to zero by definition. The reaction is no longer spontaneous in either direction.

93.

All of the following are basic SI units, except:

  • Pound (lb)

  • Kelvin (K)

  • Meter (m)

  • Second (s)

  • Mole (mol)

Correct answer: Pound (lb)

Weight is expressed in grams, kilograms, etc. in chemistry. If you are provided with a quantity in ounces or pounds, be careful; many standard chemical formulas assume you are working with SI units.

94.

You make a solution that is 3.0M HCl. Now, you want to make an even stronger acidic solution: 6.0M HCl. Which of the following would be appropriate ways to do this?

i. Double the amount of HCl

ii. Double the volume by adding water

iii. Pour out half the solution

  • i. only

  • iii. only

  • i. and iii.

  • i. and ii.

  • i., ii., and iii.

Correct answer: i. only

To increase from 3.0M to 6.0M HCl, you need to double the concentration of HCl. This is accomplished most simply by adding more HCl to your existing solution. If you poured out half the solution, you would still have a 3.0M solution (though you would have less of it). If you added water, you would dilute your solution 1.5M.

95.

Write the following word equation in appropriate chemical symbols:

sodium hydroxide plus hydrochloric acid yields sodium chloride plus water

  • NaOH + HCl --> NaCl + H2O

  • NaOH + HClO --> NaClO + H2O

  • Na(OH)2 + HCl --> NaCl2 + H2O

  • Na(OH)2 + HClO --> Na(ClO)2  + H2O

  • NaOH + H2Cl --> NaCl + H2O

Correct answer: NaOH + HCl --> NaCl + H2O

It is helpful to know that all ions involved in this reaction are +1 or -1 ions, so only one of each is needed. The correct equation is already balanced.

96.

What type of reaction is this?

Ag+ + e- --> Ag

  • Reduction

  • Oxidation

  • Synthesis

  • Combination

  • Acid/base

Correct answer: Reduction

Technically, this is a "half reaction" because an oxidation must be occurring as well; that is what supplied the electron. A reduction involves the gain of an electron, while an oxidation involves the loss of an electron. The two types of half reactions are always paired together.

97.

All of the following organic functional groups contain a C=O double bond, except:

  • Ether

  • Ester

  • Ketone

  • Aldehyde

  • Carboxylic acid

Correct answer: Ether

An ether is comprised of O single-bonded to two C atoms, such that O looks like it is part of an otherwise carbon chain.

98.

What kind of reagent is needed to make the following change occur?

Zn  ZnCl2

  • Oxidizing agent

  • Reducing agent

  • Halogenated agent

  • Gaseous agent

  • Precipitating agent

Correct answer: Oxidizing agent

Consider the oxidation states involved: Zn is 0 on the left and +2 on the right. It is therefore oxidized, and this process requires an "oxidizing agent." (It is true that Cl, a halogen, must also be introduced, but "halogenated agent" is not a standard category of reagents.)

99.

You have liquid water in a pot and want to make it boil at a temperature below 100°C (water's standard boiling point). Which of the following would help you accomplish this?

i. Take the pot to the top of a mountain

ii. Seal the pot inside a vacuum chamber and decrease the pressure

iii. Pour out some of the water

iv. Add salt to the water

  • i. and ii.

  • i., ii., and iv.

  • iii. and iv.

  • i., ii., and iii.

  • None of these; water cannot boil below 100°C

Correct answer: i. and ii.

For any substance under any condition, boiling occurs when the liquid's vapor pressure equals atmospheric pressure. Therefore, you can adjust the temperature at which water boils by manipulating the vapor pressure or the atmospheric pressure. A vacuum chamber would allow you to reduce atmospheric pressure artificially; a mountaintop would have naturally lower atmospheric pressure.

The addition of salt actually decreases the vapor pressure because the salt is non-volatile, so this would raise the boiling temperature. Pouring out water does not affect vapor pressure nor atmospheric pressure; though a smaller volume of water takes less time to boil, it ultimately boils at the same temperature as a larger volume.

100.

How many significant figures are in 0.005930?

  • 4

  • 3

  • 5

  • 6

  • 7

Correct answer: 4

Non-zero numbers are always significant. Zeros are significant unless they are 1) before the decimal point, or 2) after the decimal point but before the first non-zero number.

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