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Quiz Session - Attempts With Random Questions

College Chemistry Exam Questions

Page 9 of 25

161.

You need to dilute 6M HCl to make 3M HCl. How should you do this (safely)?

  • Fill a separate beaker with the same volume of water as you have 6M HCl, then pour the HCl into the water

  • Measure out the same volume of water as you have 6M HCl, then pour the water into the HCl

  • Pour out half of the HCl in an acid waste repository

  • Add 100mL 6M HCl and 100mL water to a centrifuge tube, and spin

  • Pour half of the HCl down a drain

Correct answer: Fill a separate beaker with the same volume of water as you have 6M HCl, then pour the HCl into the water

To dilute 6M HCl to 3M HCl, you need to double the water concentration in the HCl solution. When working with strong acids, however, it is important to always "add acid": pour the acid into the water, rather than the other way around. Pouring water into acid can lead to a violent, dangerous boiling reaction.

162.

What is meant by "standard state"?

  • 298K, 1atm

  • 273K, 1atm

  • 300K, 1atm

  • 298K, 0atm

  • 373K, 0atm

Correct answer: 298K, 1atm

These conditions essentially represent room temperature and normal atmospheric pressure. Since the free energy of reactions depends on the reaction conditions, "standard state" is used to provide standardized free energies for many common reactions. If you look up reactions in a free energy table, make sure to note whether standard state or a different set of conditions is used.

163.

Is the 4s subshell filled before or after the 3d subshell?

  • Before

  • After

  • Depends on the element

  • It is determined randomly (they are roughly equivalent in energy)

  • Unable to determine without more information

Correct answer: Before

It is important to remember that electrons fill the lowest energy orbitals first, and the lowest energy does not always go in order of shell number! It may be helpful to use a diagram to learn the order.

164.

In a coordinate covalent bond, both electrons in the bond come from the same atom. What must be true of the atom that did not contribute any electrons?

  • It is a Lewis acid

  • It already has a full octet

  • It is hydrogen

  • It is a Bronsted-Lowry base

  • It is very electron-rich

Correct answer: It is a Lewis acid

The Lewis definition of acids and bases focuses not on protons, but on the ability to receive or donate electron pairs. In a coordinate covalent bond, the electron-donor is a Lewis base while the electron-recipient is a Lewis acid.

165.

It is an often-repeated rule: Carbon can only form 4 bonds. And yet, some atoms form 5 or 6 bonds. Which atoms can do this?

  • Atoms with quantum number >= 3

  • Atoms with quantum number >=5

  • Atoms in the d-block

  • Atoms along the stair-step line

  • Any atoms; it is just not very stable for small atoms like carbon

Correct answer: Atoms with quantum number >= 3

Starting in Period 3, atoms gain d-orbitals. While Period 2 atoms bond only with s and p orbitals, Period 3 atoms can bond with d-orbitals, forming up to six bonds. For example, phosphorous often forms five bonds, and silicon often forms six.

166.

What is a reasonable range for an acetic acid buffer (pKa = 4.75)?

  • 3.75-5.75

  • 4.25-5.25

  • 4.7-4.8

  • 3-6

  • 2.75-6.75

Correct answer: 3.75-5.75

A buffer is most effective within one deviation in pH from the buffer's pKa. For all buffers, this yields a range of 2 pH degrees within which the buffer is reasonably effective.

167.

Consider the following reaction and expression for the equilibrium constant:

HCl(g)+NaOH(aq)⇌NaCl(aq)+H2O(l), K = ([NaCl][H2O])/[HCl][NaOH])

What is wrong?

  • Water should not be included in the expression for K

  • Water should not be included in the balanced equation

  • HCl(g) should not be included in the expression for K

  • This reaction should be written with only a forward arrow, not as an equilibrium

  • The expression for K should be inverted

Correct answer: Water should not be included in the expression for K

K accounts for only solutes and gases, but not pure liquids or solids. Therefore, HCl (g) should be included, but water should not. It is important, however, to include water in the chemical equation because it is part of the balanced reaction as the sink for HCl's protons.

168.

Which set of descriptors best describes an element to the left of the stairstep line on the periodic table?

  • Malleable, ductile, electrical conductor, solid at room temperature

  • Malleable, brittle, electrical conductor, liquid at room temperature

  • Brittle, ductile, non-conductor, solid at room temperature

  • Brittle, non-malleable, electrical conductor, solid at room temperature

  • Malleable, ductile, non-conductor, liquid at room temperature

Correct answer: Malleable, ductile, electrical conductor, solid at room temperature

Metals fall to the left of the stairstep line and are generally malleable (can be beaten into sheets without breaking), ductile (can be pulled into wires), and good conductors of electricity. They are all solid at room temperature with the notable exception of mercury (liquid).

169.

In which location would a liquid have the highest boiling point?

  • Surface of Venus (9200 kPa)

  • Earth at sea level (101.3 kPa)

  • Earth at the top of Mt Everest (33.7 kPa)

  • Surface of Mars (0.6 kPa)

  • A liquid would boil at the same temperature anywhere

Correct answer: Surface of Venus (9200 kPa)

Boiling occurs when a liquid's vapor pressure = atmospheric pressure, so it has the highest boiling point when it is under the highest atmospheric pressure.

170.

What would be a reasonable first step in balancing the following equation?

Pb(OH)4 + H2SO4 → Pb(SO4)2 + H2O

  • Any of these

  • Adjust the coefficient of H2SO4

  • Adjust the coefficient of H2O

  • Create a table to track each element on both sides of the reaction

  • None of these

Correct answer: Any of these

There are many ways to balance reactions, all of which can produce the correct final answer. Some people find it helpful to write a tracking table; others can keep count in their heads. In this equation, it would be reasonable to start with the unequal numbers of S, H, or O and go from there.

171.

Mitochondria in our cells produce ATP, the energy currency we need to live, through a set of processes that begin with cellular respiration. The net equation for respiration follows. What fundamental type of reaction is this biological process?

C6H12O6 + O2 → CO2 + H2O

  • Combustion

  • Acid-base

  • Combination

  • Decomposition

  • Single replacement

Correct answer: Combustion

The body's cells regularly use a combustion reaction to produce energy. This should make intuitive sense because combustion releases a great deal of energy; this energy can then be harnessed in the form of ATP. It is also a redox reaction (oxygen is reduced, carbon is oxidized).

172.

What coefficients would balance the following equation?

__PCl5 + __H2O → __H3PO4 + __HCl

  • 1, 4, 1, 5

  • 1, 3, 2, 5

  • 1, 6, 4, 5

  • 2, 4, 2, 10

  • 2, 4, 3, 5

Correct answer: 1, 4, 1, 5

Start by balancing the atoms that appear only once on both sides of the equation:

PCl5 + H2O → H3PO4 + 5HCl

Then balance the hydrogen and oxygen atoms accordingly:

PCl5 + 4H2O → H3PO4 + 5HCl

173.

Which of the following organic functional groups would you expect to be most acidic (lowest pKa)?

  • Carboxylic acid

  • Alkane

  • Alkyne 

  • Aldehyde

  • Ketone

Correct answer: Carboxylic acid

Carboxylic acid contains a terminal -OH group that loses its proton easily. The resulting negative charge can be stabilized by the adjacent C=O double bond. None of the other answer choices are remotely acidic.

174.

Under what general conditions does a substance transition directly between solid and gas without passing through the liquid phase?

  • Relatively low temperature and low pressure

  • Relatively high temperature and high pressure

  • Relatively low temperature and high pressure

  • Relatively high temperature and low pressure

  • It is impossible to transition directly between solid and gas

Correct answer: Relatively low temperature and low pressure

These phase transitions are called sublimation (solid to gas) and deposition (gas to solid). Water, for example, undergoes deposition when it forms snow. This occurs when atmospheric conditions are very cold (hence, why snow occurs only in the winter) and low-pressure.

175.

How many oxygen atoms are present in 4Cr(NO3)3?

  • 36

  • 3

  • 9

  • 12

  • 27

Correct answer: 36

Pay attention to coefficients and subscripts. Coefficients apply to every atom in the molecule that follows (i.e., there are 4 Cr, 12 N, and 36 O). Subscripts apply only to the atom that precedes the subscript, or to everything inside the parenthesis preceding the subscript.

176.

You have two gas samples and want to know which has the higher temperature. If you do not have a thermometer, which other piece of information could you use?

  • Each sample’s average kinetic energy

  • The atomic radius of each gas

  • The pressure in each sample’s container

  • Each sample’s range of kinetic energies

  • The volume occupied by each sample

Correct answer: Each sample’s average kinetic energy

Temperature is simply a measure of average kinetic energy. In other words, as temperature increases, gaseous molecules move faster and faster. So if you can compare how fast each sample is moving, you can determine which is at the higher temperature.

177.

Period 6 is called the:

  • Actinides

  • Lanthanides

  • Allurilides

  • Lurbidamides

  • Lacithanides

Correct answer: Actinides

Periods 6 and 7 are the Actinides and the Lanthanides, respectively. They are usually displayed at the bottom of the periodic table and have very different behaviors from the elements toward the top of the periodic table.

178.

You wrote down that your solution increased in temperature by 38, but you forgot to write units. How are the units of °F, °C, and K related to each other?

  • 1°C and 1K are identical and larger than 1°F

  • 1°C and 1°F are identical and smaller than 1K

  • 1°F, 1°C, and 1K are all different

  • 1°C and 1K are identical and smaller than 1°F

  • 1°C and 1°F are identical and larger than 1K

Correct answer: 1°C and 1K are identical and larger than 1°F

If your solution increased by 38°C or 38K, these changes are identical. Celsius and Kelvin span different numerical ranges, but both contain 100 units between the melting and freezing points of water (0-100°C, 273-373K). In contrast, 1°F represents a smaller change than 1°C or 1K.

179.

Though we often use "weight" and "mass" interchangeably, they have different meanings and even different types of units. What is the SI unit of weight?

  • Newton

  • Pound

  • Kilogram

  • Meter

  • Second

Correct answer: Newton

The Newton, N, is the SI unit for force, defined in terms of (kg*m)/(s^2). Though we colloquially say "weight" to mean "mass," the technical meaning of "weight" is (mass)(acceleration due to gravity). You will not usually have to convert between pounds and Newtons, but 1 Newton =  0.225 pounds.

180.

When considering ionization energy, some chemists talk about a quantity called “Zeff.” What does this mean?

  • The effective nuclear charge felt by valence electrons

  • The effective nuclear charge felt by the inner-most electrons

  • The total number of protons

  • The number of protons minus the number of electrons

  • The number of protons plus the number of neutrons

Correct answer: The effective nuclear charge felt by valence electrons

On the periodic table, Z is the number of protons, and A is the atomic mass (roughly, protons + neutrons).  Zeff considers the fact that electrons further away from the nucleus cannot feel the full effect of all the protons because inner electrons "shield" the outer ones from the protons' charge. Therefore, Zeff is the nuclear charge experienced by an electron that could potentially leave, and ionization energy increases as Zeff increases.

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