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mcat > gchem 3 > Flashcards

gchem 3 Flashcards

1
Q

What is the difference between a reducing agent and an oxidizing agent?

A

oxidizing - atom or molecule that accepts electrons

reducing - atom or molecule that donates electrons

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2
Q

What is the oxidation state of any elemental atom?

A

0

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3
Q

What is the oxidation state of fluorine?

A

-1

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4
Q

What is the oxidation state of hydrogen?

A

+1

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5
Q

What is the oxidation state of hydrogen w a metal?

A

-1

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6
Q

What is the oxidation state of oxygen?

A

-2

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7
Q

What is the oxidation state of alkali metals?

A

+1

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8
Q

What is the oxidation state of alkaline earth metals?

A

+2

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9
Q

What is the oxidation state of group V atoms?

A

-3

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10
Q

What is the oxidation state of group VI atoms?

A

-2

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11
Q

What is the oxidation state of group VII atoms?

A

-1

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12
Q

What is electrical potential?

A

degree of which a species “wants electrons” or “wants to be reduced”

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13
Q

A species that has a positive electrical potential is more likely to __ ___

A

gain electrons

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14
Q

A species with a negative electrical potential is __ ___ to gain electrons

A

less likely

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15
Q

What is cell potential?

A

E°cell is the sum of the electrical potentials for the two half-reactions that make up an electrochemical cell

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16
Q

The oxidation half-reaction is the __ of the reduction half reaction

A

reverse

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17
Q

you CANNOT add two E° values directly off of a half-reaction table, so you need to _____

A

you must reverse the half-reaction of the species with the lowest reduction potential and take the negative of its E° value. Only after changing the sign can you add these two together to get the E°cell

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18
Q

When calculating cell potential DO NOT use __

A

Stoichiometry

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19
Q

Would you expect a strong oxidizing agent to have a high or a low reduction potential?

A

it would have a high reduction potential (it wants to gain electrons to oxidize a different molecule)

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20
Q

What is the galvanic cell?

A

Galvanic cells convert chemical energy into electrical energy. By taking advantage of the difference in reduction potentials between two metals, a current can be spontaneously generated along a wire that connects two metal electrodes submerged in solutions that contain metal ions.

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21
Q

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

A

neutralizes the build up of charge between the two cells so it doesn’t shut down

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22
Q

In all electrochemical cells, __ always happens at the cathode and __ always happens at the anode

A

reduction, oxidation

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23
Q

What is an electrolytic cell?

A

Essentially, a galvanic cell to which an external voltage is applied, forcing the electrons to flow in the opposite direction.

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24
Q

the cell potential in electrolytic cells is always ___

A

NEGATIVE (opposite for galvanic cells)

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25
Q

In electrolytic cells, the sum of the externally applied voltage and the negative cell potential must be ___

A

positive

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26
Q

in electrolytic cells, the cathode has a __ charge and the anode has a ___ charge

A

negative, positive

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27
Q

What is a concentration cell?

A

A concentration cell is an electrolytic cell that is comprised of two half-cells with the same electrodes, but differing in concentrations. A concentration cell acts to dilute the more concentrated solution and concentrate the more dilute solution, creating a voltage as the cell reaches an equilibrium. This is achieved by transferring the electrons from the cell with the lower concentration to the cell with the higher concentration.

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28
Q

By definition, in a concentration cell, electrical potential will always equal __

A

0

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29
Q

What is the Nernst equation? What is it used to calculate?

A

E = E° - (0.06/n)*log[lower]/[higher];
where n = moles of electrons transferred

cell potential based off the E ̊ of the species and the concentrations of the two solutions

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30
Q

What is the equation that relates free energy to chemical energy?

A

∆G° = -nFE°; where n is the number of moles of electrons transferred in the balanced redox reaction, and F is Faraday’s constant.

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31
Q

what is Faraday’s constant?

A

9.6 x 10^4 C/mol

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32
Q

What is the difference between a faraday and a farad?

A

faraday - equal to the charge on one mole of electrons

farad - amount of capacitance necessary to hold 1 C of charge on a capacitor with a potential difference of 1 Volt.

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33
Q

What is the equation for the ideal gas law?

A

PV = nRT ; R = 0.0821 Latm/molK or 8.314 J/mol*K

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34
Q

What are the ideal gas law assumptions?

A
  1. gas molecules themselves are of negligible volume compared to the volume occupied the gas
  2. all intermolecular forces between gas molecules are negligible
  3. all collisions between gas molecules are perfectly elastic
  4. gas molecules are far from each other
  5. pressure is due to collisions
  6. all motion is random
  7. all molecular motion follows Newton’s laws of motion
  8. the avg. KE of gas is proportional to temp
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35
Q

What are the conditions for STP (standard temperature and pressure)? (for ideal gas law)

A 
P = 1 atm 
V= 22.4 L
n = 1 mole
R = 0.0821 L*atm/mol*K or 8.31 J/mol*K
T = 273 K
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36
Q

What is the difference between STP and standard conditions?

A

standard conditions are used when measuring thermodynamic data, reduction potentials, etc. STP - ideal gases

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37
Q

What is the equation for the combined gas law?

A

P1V1/T1 = P2V2/T2

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38
Q

The greatest deviation between ideal gas behavior and real gas behavior occurs when either ___ or ___

A

the temp is extremely low

pressure is extremely high

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39
Q

In the van der waal’s equation, [P + a’(n/V)^2]*[(V/n) – b’] = RT, what does a’ and b’ mean?

A

a’ = constant that represents the actual strength of the intermolecular attractions

b’ = constant that represents the actual volume of the molecules

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40
Q

in real gases, increased intermolecular attractions (a’), ___ pressure

A

decreases

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41
Q

In real gases, increased molecular volume (b’), ___ volume

A

increases

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42
Q

If PV/nRT > 1, which assumption is the major cause of deviation from ideal gas law?

A

due mostly to the molecular volume assumption

43
Q

If PV/nRT < 1, which assumption is the major cause of the deviation from the ideal gas law?

A

intermolecular forces assumption

44
Q

What is Dalton’s Law of Partial Pressures?

A

Ptotal = P1 + P2 + P3 . . .

45
Q

What is the difference between effusion and diffusion?

A

Diffusion - process by which gas molecules spread from areas of high concentration to areas of low concentration due to the random motion imparted to them as a result of their kinetic energy and collisions with other molecules.

effusion - diffusion of gas particles through a pin hole. A pin hole is defined as a hole smaller than the average distance a gas molecule travels between collisions

46
Q

rate of effusion is __ proportional to the molecular weight of gas

A

inversely

47
Q

What is the equation for Grahams law? (effusion and diffusion)

A

E1/E2 = √MW2 / √MW1

E1 and E2 - represent effusion or diffusion rate of gases 1 and 2

48
Q

How many unique phases are present in a sealed reaction vessel containing sodium chloride solution?

A

2 - liquid of the solution and vapor above the solution

49
Q

What is ΔHfusion?

A

The amount of energy in Joules/mole required to go from solid to liquid or the energy that must be removed to go from liquid to solid. This describes the transition in both directions (i.e., melting and freezing).

50
Q

solid -> liquid

A

melting

51
Q

liquid -> solid

A

freezing

52
Q

liquid -> gas

A

evaporating

53
Q

gas -> liquid

A

condensation

54
Q

solid -> gas

A

sublimation

55
Q

What is ΔHvaporization?

A

The amount of energy in Joules/mole required to go from liquid to gas OR the energy that must be removed to go from gas to liquid. Again, it describes both evaporation and condensation.

56
Q

gas -> solid

A

deposition

57
Q

What is melting point? boiling point?

A

melting - temperature at which a substance changes state from solid to liquid (freezing and melting pt are same)

boiling - temperature at which a
substance changes state from liquid to gas

58
Q

What does volatile vs non volatile mean?

A

volatile - the relative tendency of a substance to form a vapor

non volatile - substance does not form a vapor, or has an extremely low vapor pressure, at room temperature

59
Q

What is the triple point of a phase diagram?

A

precise temperature and pressure at which all three phases (i.e., states) exist simultaneously in equilibrium with each other

60
Q

What is the critical point in a phase diagram?

A

precise temperature and pressure above which liquid and gas phases become indistinguishable

61
Q

What is the supercritical fluid of a phase diagram?

A

cannot be compressed back into the liquid phase by increasing pressure, nor can it be turned into a gas by increasing temp (at the critical point)

62
Q

What is the critical temp and pressure of a phase diagram?

A

they are at the critical point

63
Q

Compare the heat of vaporization at the triple point to the heat of vaporization at the critical point. Which value will be larger?

A

The heat of vaporization is the enthalpy change associated with the transition between liquid and gas. Whatever that might be at or near the triple point, it does not exist at the critical point.

By definition, at the critical point a liquid cannot be changed into a gas, so the heat of vaporization would be zero. Any value is greater than zero, therefore, the heat of vaporization
will always be greater at the triple point.

64
Q

How do you calculate the ΔH from a heating curve? For ΔHfusion? For ΔHvaporization?

A

ΔHfusion - the change in q (x axis) during the phase change from solid to liquid

ΔHvaporization- the change in q (x-axis) during the phase change from liquid to gas

65
Q

There is ___ in temperature during a phase change

A

no change

66
Q

What is vapor pressure?

A

partial pressure of the gaseous form of a liquid that exists over
that liquid when the liquid and gas phases are in equilibrium

67
Q

How is vapor pressure affected by temperature?

A

increased temp increases vapor pressure

68
Q

How does the addition of a non-volatile solute affect vapor pressure?

A

decreases vapor pressure

surface of liquid evaporates, so if surface is occupied by non-volatile solute, less evaporation will occur

69
Q

How does adding a volatile solute affect vapor pressure?

A

decreases vapor pressure

As long as the vapor pressure of the solute is LESS THAN the vapor pressure of pure solvent, addition of the volatile solute will
decrease vapor pressure. However, if a solute is added that has a vapor pressure greater than that of the pure solvent, then the vapor pressure of the solution will actually be higher than that of the pure solvent

70
Q

What two quantities are equal when a liquid boils?

A

A liquid boils when the vapor pressure of that liquid is equal to atmospheric pressure

71
Q

What is the equation for Raoult’s law for vapor pressure w/ non volatile solute?

A

(mole fraction of the pure solvent ,X)*(Vp of the

pure solvent, Vp°)

72
Q

What is the equation for Raoult’s law for total Vp w/ volatile solute?

A

(mole fraction of solvent * Vp°of the solvent) + (mole fraction of the solute* Vp° of the solute)

73
Q

What is Henry’s Law?

A

Primarily used to describe the solubility or partial vapor pressure of gases dissolved in liquids

Vapor partial pressure of solute = (mole frac. of solute)* (henry’s law constant)

74
Q

The solubility of a gas in a liquid is ____ proportional to the partial pressure of that gas over that liquid

A

directly

75
Q

For gas solubility, increased temp results in __ solubility of gas X in a liquid

A

decreases

76
Q

For gas solubility, increasing the vapor pressure of gas over a liquid __ the solubility of gas in that liquid

A

increases

77
Q

In gas solubility, polar and non polar gases ___ homogenous mixtures

A

easily form

78
Q

What is boiling point elevation?

A

boiling point increases when a non-volatile solute is added

∆T = kbmi
kb is a constant
m is molality (NOT molarity)
i is the number of ions formed per molecule (a.k.a., The Van’t Hoff Factor; i.e., for NaCl i = 2; for CaCl2 i = 3).

79
Q

What is freezing point depression?

A

The freezing point of a liquid is depressed when a non-volatile solute is added according to:

∆T = kfmi ; where kf is a new constant, different than kb above.

80
Q

What is osmotic pressure?

A

A measure of the tendency of water to move from one solution to another across a semi-permeable membrane

(it is the side that will RECEIVE the water via osmosis that has the higher osmotic pressure)

81
Q

How to calculate osmotic pressure?

A 
iMRT 
i = # of ions formed in solution
M is the solute molarity
R is the gas constant
T is the absolute temperature.
82
Q

What is a solution?

A

homogenous mixture of two or more compounds in the same phase. (We usually think of all solutions as being in the liquid, or “aqueous” phase; however, a homogenous mixture of gases is also called a “solution”.)

83
Q

What are colloids?

A

Colloids are NOT solutions. Colloids are solvents containing undissolved solute particles that are too small to be separated by filtration, but are much larger than the solute particles in a true solution. Colloids scatter light, while true solutions do not. Examples of colloids include paint (a suspension of solid crystals in a solvent) and dust floating in ai

84
Q

What is molality?

A

moles of solute/ Kg of solvent

85
Q

What is mole fraction?

A

moles of solute/ total moles of solution (solute + solvent)

86
Q

What is mass percent?

A

mass of solute/ total mass of solution * 100

87
Q

What is ppm?

A

mass solute / total mass solution * 10^6

88
Q

What is the molecular formula for nitrite, nitrate, chlorate, chlorite, hypochlorite, and perchlorate?

A 
nitrite - NO2-
nitrate - NO3-
chlorate - ClO3-
chlorite - ClO2- 
hypochlorite - ClO-
perchlorate - ClO4-
89
Q

What is the molecular formula for carbonate and bicarbonate?

A

carbonate - CO3 2-

bicarbonate - HCO3-

90
Q

What is the molecular formula for manganate, permanganate, and cyanide?

A

cyanide - CN-
permanganate - MnO4-
manganate - MnO4 2-

91
Q

What does hydration number mean? What is a hydrate?

A

hydration number - number of water molecules an
ion can bind via this solvation process, effectively removing them from the solvent and causing them to behave more like an extension of the solute

hydrate - inorganic compound in
which water molecules are permanently bound into the crystalline structure

92
Q

What does anhydrous mean?

A

applied to a compound that can form complexes with water to differentiate molecules that do not contain water from those that do

93
Q

What is normality in solutions?

A

of moles of equivalents/ L solution

94
Q

If the new intermolecular forces formed are more stable than the sum of the intermolecular forces that had to be broken, net energy is ___ and the solution is said to have a __

A

released, negative Heat of Solution

95
Q

How does entropy change when a solution forms?

A

The dissolution of a solute into a solution is accompanied by a very large, positive change in entropy. A solid or crystal is highly ordered and the break-up and solvation of that solid into individual molecules represents a significant increase in disorder.

96
Q

What is the difference between a saturated, unsaturated and supersaturated solution?

A

saturated - contains the max amount of dissolved solute it can hold
unsaturated - solution that contains less than its max amount of dissolved solute
supersaturated - solution is held at a higher temperature during dissolution and then slowly cooled to a temperature at which Ksp is smaller

97
Q

What does like dissolves like mean?

A

polar substances are soluble in polar solvents, vis versa for non polar substances

98
Q

The only factor that changes Ksp?

A

temperature

99
Q

What is the difference between solubility and the solubility product constant?

A

solubility - measure of “how much” of a solute can be dissolved

solubility product constant (Ksp) - the product of the dissolved ions in a saturated solution raised to their coefficients in the balanced equation

Ksp and solubility are directly related
the higher the Ksp the greater the solubility

100
Q

What is the ion product?

A

“solubility product”

plug in values for actual concentrations of each species (do products over reactants)

if ion product > Ksp, precipitate will form
if ion product < Ksp, no precipitate will form

101
Q

What is the common ion effect?

A

When dissolving an ionic compound, if another ionic compound with the same ions will shift the equation left to form precipitate

other ions that don’t shift equilibrium are called spectator ions

102
Q

How to calculate solubility

A
  1. write out Ksp expression
  2. substitute into the expression the value given for Ksp
  3. substitute a factor of x into the equation for the concentration of each ion
  4. solve for x
103
Q

All compounds containing the following are SOLUBLE : ___

A

nitrate, ammonium, and all alkali metals (Group IA).

104
Q

All compounds containing the following are INSOLUBLE: ___

A

carbonate, phosphate, silver (Ag), mercury (Hg), and lead (Pb).

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