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MCAT > General Chemistry - TRP Review Questions > Flashcards

General Chemistry - TRP Review Questions Flashcards

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1
Q

What are the three fundamental particles of matter? And which determines the identity of an element?

A

Neutron

Proton

Electron

The # of protons determines the identity

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2
Q

Isotopes differ by the number of which fundamental particle?

Which particle(s) is the mass number of an element determined by?

A

Same number of protons, different number of neutrons. Differ by the number of neutrons.

of protons plus # of neutrons in an atom

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3
Q

There are two types of ions. Identify them by name and their type of charge

A
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4
Q

What letter stands for the principal quantum number? What is the range of possible values for this number?

Define the principal quantum number

A

The letter “n”

n = 1 to n=infinite

The principal quantum number is the quantum number denoted by n and which indirectly describes the size of the electron orbital. It is always assigned an integer value (e.g., n = 1, 2, 3…), but its value may never be 0. An orbital for which n = 2 is larger, for example, than an orbital for which n = 1. Energy must be absorbed in order for an electron to be excited from an orbital near the nucleus (n = 1) to get to an orbital further from the nucleus (n = 2).

The principal quantum number is cited first in the set of four quantum numbers associated with an electron. The principal quantum number has the greatest effect on the energy of the electron. It was first designed to distinguish between different energy levels in the Bohr model of the atom but remains applicable to the modern atomic orbital theory

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5
Q

The ground state electron configuration of any element can be determined by following three rules of electron filling.

What are they and how do they determine the location of electrons in an atom?

A

The Aufbau Principle: fill lower enegy levels and sublevels before adding electrons to higher energy (sub)levels.

Pauli Exclusion Principle: there are a maximum of 2 electrons per orbital, and they must have opposite spins

Hund’s Rule: half fill orbitals of equal energy before pairing electrons in any one orbital in a given subshell.

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6
Q

State the three properties of electromagenetic radiation:

A

Frequency

Wavelength

Energy

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7
Q

Define Quantized

A

Only comes in certain discrete sizes (for ex: cannot be divide by 2. Electron mass is quantized, cannot be broken in half so cannot be divided in half)

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8
Q

Name the three main types of nuclear decay from least to most damaging to tissue:

A

(least damaging) Alpha < Beta < Gamma (most damaging)

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9
Q

One type of nuclear decay has three different modes. What are they?

A

Beta: B- (normal beta decay)

B+ : positron emission

EC: Electron capture

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10
Q

What are the five periodic trends?

A

Electronegativity

Atomic size

Electron affinity

First ionization energy

Acidity/Basicity

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11
Q

What are the 3 kinds of covalent bonds?

A

Normal (which can be polar or nonpolar)

Metallic

Coordinate covalent bonds

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12
Q

Give 2 other names for Lewis Bases

A

Ligand, nucleophile, or chelator

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13
Q

What three geometric family names are associated with each type of hybridized orbitals?

A

Linear : sp

Trigonal planar: sp2

Tetrahedral: sp3

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14
Q

Name the various intermolecular forces, from strongest to weakest

A

Strongest

Hydrogen bonding

Dipole-dipole forces

London dispersion forces

Weakest

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15
Q

What are the phases of matter (disregarding plasma)?

A

Gas
Liquid

Solid

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16
Q

When energy is added to a substance, that energy can be used to do one of two physical things. What are they?

A

Increase the temperature (increase Kinetic Energy)

Cause a phase change (Increase Potential Energy)

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17
Q

What two things does vapor pressure depend on?

A

Temperature and intermolecular forces

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18
Q

When does a liquid boil?

A

When the hydrogen bonds or other intermolecular forces no longer can hold molecules together.

When vapor pressure of liquid = atmospheric pressure

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19
Q

The phase of a substance depends on what two properties besides intermolecular forces?

A

Temperature

Pressure

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20
Q

What assumptions do we make about ideal gases?

A

Take up no volume

and

Experience no intermolecular forces

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21
Q

What do the constants a and b accound for in the van der waals equation for real gases?

What is the van der waals equation?

A

The constant a accounts for the intermolecular forces between gas molecules and b accounts for the molecular volume of the gas particles

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22
Q

What conditions are indicated by the letter STP?

A

Standard Temperature and Pressure:

Temperature = 0 degrees Celsius

Pressure = 1 atm

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23
Q

What is the volume of 1 mole of an ideal gas at STP?

A

22.4 L

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24
Q

Describe at a molecular level what happens to a solid when it dissolves

A

Dissociation

Solvent molecules interact with ions

(solute particles are separated and encapsulated by solvent molecules such that the solute is observed to dissolve)

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25
Q

Define electrolyte

A
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26
Q

What is the difference between an intermediate and a transitions state?

A

An intermediate is found at local energy minima along a reaction coordinate while transition states are at local energy maxima along a reaction coordinate. Transition states are the highest energy species in a reaction because bonds are breaking and forming, so it cannot be isolated from a reaction.

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27
Q

What is the minimum energy required to start a reaction?

A

The activation energy Ea must be reached before a reaction can proceed.

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28
Q

What three properties affect the rate of a reaction?

A

Temperature

[Concentration] (or for gases, partial pressure)

Activation Energy

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29
Q

What are the two ways to determine the order of a rate law?

A
  1. A multitrial experiment in which the concentration of one reagent is changed over time
  2. Looking at the rate-determining step in a previously proposed mechanism

CAN ONLY BE DETERMINED EXPERIMENTALLY

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30
Q

What does it mean for a reaction to be at equilibrium?

A

The rate of the reaction in the forward direction is equal to the rate of reaction in the reverse direction (or the concentrations of reactants and products do not change with respect to time)

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31
Q

What types of substances are included in an equilibrium constant (K) expression?

What types of substances are excluded?

A

gases and aqueous solutions are included

liquids and solids are excluded (or if solution has an extremely small concentration can treat as liquid)

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32
Q

State the three ways to disturb or stress a chemical equilibrium

A
  1. Add or remove heat
  2. Change volume (aka add or remove pressure)
  3. Add or remove product or reactant (change concentration)
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33
Q

What is the only way to change the equilibrium contant, K value?

A

Change the temperature

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34
Q

Name the strong acids and strong bases:

A

Strong Acids

HCl

HBr

HI

HNO3

HClO4

H2SO4

Strong Bases

Group 1 Hydroxides (ex: NaOH)

Ba/Sr/Ca hydroxides

Metal amides

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35
Q

Define a conjugate pair

A

Two molecules/ions that differ by one H+

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36
Q

What is the pH scale?

Where do acids and bases fall on the scale?

A

pH scale measures acidity and basicity of molecules. Based on hydrogen

Acids are low numbers (less than 7)

Bases are high numbers (greater than 7)

7 is neutral

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37
Q

How is the pH of a strong acid calculated?

A

pH = -log[H+]

Which is the same as -log[acid] since strong acids completely dissociate

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38
Q

Give three reasons why a titration might be performed:

A
  1. To determine the concentration of an unknown acid or unknown base
  2. to create a buffer
  3. to determine the pKa (or pKb) of an unknown weak acid (or weak base) nad perhaps thereby identify the acid or base as well
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39
Q

What is the equivalence point of a titration?

A

The point at which pH = pKa

40
Q

What is a buffer?

A

A solution that resists change to pH

41
Q

What happens to the pH of a buffer when it is diluted?

When concentrated?

A

The pH does not change upon the addition or removal of solvent because relative concentrations of the acid and conjugate base in solution change proportionately, so their ratio does not change.

42
Q

identify the standard state conditions for temperature and pressure:

A

25 degrees Celsius

1 ATM

43
Q

When is the entropy of a subsance equal to zero?

A

When a pure element is solid at absolute zero (0 degrees Kelvin)

44
Q

Which process requires energy (is endothermic), breaking a bond or forming a bond?

A

Breaking a bond (absorbs energy) is endothermic

Forming a bond (releases energy) is exothermic

45
Q

Name the two parts of all electrochemical reaction, and define them based on electron transfer.

A

Oxidation: Lose electrons

Reduction: Gain electrons

46
Q

What does a positive reduction potential indicate?

A

The reduction half-reaction is spontaneous while the associated oxidation half-reaction (the reverse reaction) is non-spontaneous

47
Q

Which electrochemical cell type produces electricity from sponaneous chemical reactions, an electrolytic cell or a galvanic cell?

A

Galvanic cells use spontaneous reactions to produce electricity, which electrolytic cells use electricity to force nonspontaneous reactions to occur

(Need to look further into these concepts)

48
Q

What is the sign of each electrode in a galvanic cell? An electrolytic cell?

A

In a galvanic cell, the cathode is positive and the anode is negative.

In an electrolytic cell, the electrode signs are reversed. (WHY?)

49
Q

Give two examples of elements that do not obey the Aufbau Principle

A

Chromium (Cr) and its family members or Copper (Cu) and its family members

(why don’t they obey it?)

50
Q

Which electrons do transition metal atoms lose first when they are ionized?

A

The electrons from the “s” orbital (valence s electrons)

51
Q

Explain the difference between paragmagnetics and diamagnetic elements. Give examples of each:

A

Paramagnetic:

unpaired electron

Example: N

Diamagnetic:

paired electron

Example: Ne (or any element with filled orbital subshell)

52
Q

What happens to the spacing between successively higher energy levels in an atom as you move farther from the nucleus?

A

The spacing decreases

(why is this important?)

53
Q

Describe each kind of nuclear decay

A

Alpha

Nucleus emits a helium nucleus (two protons and two neutrons

Beta

B- : a neutron converts into a proton and an electron

B+ : a proton converts into a neutron and a positron (e+ - which is emitted)

Electron Capture

A proton in the nucleus captures an inner-shell electorn and converts it into a neutron

Gamma

Excited nucleus drops to lower energy state by emitting a gamma photon

54
Q

What type of mathematical relationship is associated with radioactive decay?

A

Radioactive elements decay exponentially with respect to time

55
Q

Why is the mass of the a nucleus not equal to the individual protons and neutrons that comprise it?

A

Binding Energy or mass defect

Energy is release upon binding results in less energy that sum of constitutent parts (The binding energy that is released when the nucleons are bound together in the nucleus comes from the mass defect according to E=mc2)

56
Q

Define each periodic trend

A

Atomic Radius: Extent of the valence electrons of an atom.

Ionization Energy: Energy required to remove a mole of valence electrons from a mole of gaseous atoms of a given element.

Electron Affinity: Energy associated with adding a mole of electrons to the valence shell of a mole of gaseous atoms of a given element.

Electronegativity: A measure of the amount of “pull” an atom has on shared valence electons in a bond.

Acidity : the tendency for a molecule to give up a hydrogen atom

57
Q

Which three periodic trends follow the same pattern?

What are the trends? (need to answer)*

Why do the three trends all agree?

A

First Ionization Energy

Electron Affiinity

Electronegativity

(what are these trends on the periodic table?)*

They are all inversely related to atomic size (and thus, follow the opposite trend from atomic size)

58
Q
A
59
Q

What charge is generally associated with larger ions? With smaller ions?

A

Negative charge - larger ions

Positive charge - smaller ions

60
Q

Name at least three properties of liquids that depend on intermolecular forces:

A
  1. Solubility
  2. Vapor Pressure
  3. Boiling Point Temperature
  4. Melting Point Temperature
  5. Viscosity
  6. Surface Tension
61
Q

What quantity is specified by the average kinetic energy of the molecules of a substance?

A

Temperature

62
Q

In which phase do molecules have the most energy?

A

In the gas phase (if plasma is ignored)

63
Q

At a given temperature, which gas molecules travel faster? Those with small molecular weights or those with large molecular weights?

A

Those with small molecular weights will travel faster

64
Q

What are the official names for the six phase changes?

A

Sublimation

Condensation

Freezing

Vaporization

Melting (Fusion)

Deposition

65
Q

State the sign of ΔH and ΔS for each of the six phase changes, and rank them from highest magnitude to lowest

A

Fusion (melting): ΔH(+) ΔS(+)

Freezing ΔH(-) ΔS(-)

Condensation ΔH(-) ΔS(-)

Vaporization ΔH(+) ΔS(+)

Sublimination ΔH(++) ΔS(++)

Deposition ΔH(–) ΔS(–)

ΔHdep > ΔHcond > ΔHfreeze > 0

ΔSsub > ΔSvap > ΔSfus > 0

the ΔS and ΔH values are equal and opposite in sign based on their phase change. For example, ΔHsub = | ΔHdep |

66
Q

What happens at a molecular level when a substance changes phase?

A

Intermolecular forces are formed or broken

67
Q

What is usually the densest phase of matter?

A

Usually solid, however the main exception is: in water we find that liquid phase is denser than solid phase.

68
Q

What property is used to measure the amount of a given gas in a mixture of gases?

A

Partial Pressure

69
Q

Give an examples of a gas that most closesly approaches ideal behavior:

A

Helium (why?) (What others?)

70
Q

What temperature and pressure conditions allow most gases to behave most ideally?

A

High temperatures and low pressures (or large volumes)

71
Q

What usually happens to the solubility of solids in liquids as the temperature is increased? Why does this happen?

A

The solubility increases because solute-solute intermolecular forces weaken as solute molecules spread out due to increased vibration/kinetic energy

72
Q

How does the solubility of gases in liquids depend upon temperature and pressure?

A

The solubility of gases decreases with increasing temperature, but increases with increasing pressure

73
Q

Which ions always result in a soluble salt? Which ions generally form insoluble salts?

A

Group 1, ammonia, nitrate, acetate, and bicarbonate salts are always soluble in water.

Pb, Ag, and Hg salts are generally solible in water, unless paired with the anions previously mentioned

74
Q

What do catalysts do and how do they do it?

A

A catalyst increases the rate at which a reaction reaches equilibrium by lowering the activation energy

75
Q

What does the order of the rate law say about the reaction mechanism?

A

The number of molecules colliding in the rate-determining step

76
Q

How does the rate of a chemical reaction change with temperature?

A

As temperature increases, rate increases

As temperature decreases, rate decreases

Reaction rate ALWAYS increases with increasing temperature

77
Q

How will a catalyst affect a system that is at equilibrium

A

It won’t affect it (it won’t do anything as a catalyst only helps a reaction get to equilibrium by lowering the activation energy)

78
Q

How does the reaction quotient, Q, help determine if a reaction is at equilibrium?

A

If K = Q, then the reaction is at equilibrium.

If K < Q, the reaction will proceed in the reverse direction to reach equilibrium

If K > Q, the reaction will proceed in the forward direction to reach equilibrium

(Look at the operand; it points in the direction of the shift if K is ALWAYS kept on the left side)

K => Q (if K greater than Q, goes forward)

79
Q

What does the term strong mean in relation to an acid/base/electrolyte? What about the term weak?

A

Strong: dissociates completely (K > 1)

Weak: partial dissociation (K < 1)

All soluble salts are strong electrolytes, as are strong acids and strong bases.

Weak acids and weak bases are weak electrolytes (do not completely dissocatiate)

80
Q

What equilibrium exists in water that is shifted by the addition of an acid or a base, and what is the value of K for this reaction at standard conditions?

A

The autoionization of water, for which KW = 10-14 at standard conditions (1 ATM and 25 ºC)

(What exactly is the autoionization of water?)

81
Q

What two pieces of information are needed to calculate the pH of a weak acid?

A

The Ka of the acid and the acid concentration (using the ICEbox method).

(]H+] = sqrt(Ka[HA])

(somewhat confused on this)

82
Q

What information is needed to predict the pH at the equivalence point of a titration?

A

The strengths of the acid and base being mixed. At the equivalence point, the pH = 7 if a strong acid is mixed with a strong base. It is < 7 (less than 7) if a strong acid is mixed with a weak acid and > 7 (greater than 7) if a strong base is mixed with a weak acid.

83
Q

Describe two ways to make a buffer:

A
  1. Add roughly equal molar amounts of a weak acid and a salt of its conjugate base (or a weak base and the salt of its conjugate acid)
  2. Neutralize half of a sample of a weak acid (or base) by a strong base (or acid)
84
Q

How is the PH of a buffered solution calculated?

A

Using the Henderson-Hasselbalch Equation.

The pH of a buffer is close to the pKa of the weak acid used, and the exact pH can be determined by taking the ratio of the conjugate base to acid into consideration.

85
Q

When does pH = pKa for a buffer? What is this point called in titration?

A

When the concentrations of the weak acid and its conjugate base are equal (this occurs at the half-equivalence point in a titration experiment)

86
Q

How are the common ion effect and the mechanism of a buffer related?

A

They are the same thing, an application of Le Chatelier’s Principle

87
Q

What is the enthalpy of formation?

A

The amount of energy associated with forming one mole of a compound from its constituent elements in their standard states

88
Q

What three things must be considered to determine whether a reaction will happen, or be spontaneous?

A
  1. Change in Entropy
  2. Change in Enthalpy
  3. Change in termperature
89
Q

Describe the state of a reaction for which ΔG = 0

A

The reaction is at equilibrium

90
Q

What kind of reaction occurs at the anode of an electrochemical cell? At the cathode?

A

Oxidation occurs at the anode

Reduction occurs at the cathode

91
Q

What is the sign of the cell voltage in an electrolytic cell?

A

Negative

(why?)

92
Q

What is the purpose of the salt bridge in a galvanic cell?

A

To prevent charge separation as electrons move from one chamber to the other. The salt bridge maintains charge neutrality in each chamber.

93
Q

What is the difference between an electrolytic cell and a galvanic cell?

A

(need to look up)

94
Q

What are the common labels for a curve of a redox titration?

A

The y-axis is normally E, electric potential in volts and the x-axis is normally the amount of titrant added in mL of solution.

95
Q

What informationis required to calculate the amount of an element that can be produced in an electrolytic cell?

A

The current (in Amps), the amount of time the current is applied, Faraday’s constant, and the number of moles of electrons transferred per mole of the element formed (given by the half-reaction)

MCAT (4 decks)

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