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MCAT Chem > Chem #12 > Flashcards

Chem #12 Flashcards

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1
Q

____ Ecell means spontaneous

A

positive

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2
Q

the standard reduction potential is determined by the ____ of the electrode, not the ______

A

identity

amount of it present

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3
Q

salt bridge consists of ____

A

inert electrolytes

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4
Q

Keq depends on ____ not ____

A

Also, Keq depends on the electrolytes and the temp, not the amount of the electrode.

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5
Q

electrons flow from ________ in all types of electrochemical cells

A

anode to cathode

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6
Q

all batteries are influenced by ____

A

temperature changes

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7
Q

half cells

A

two separate compartments that contain one or the other of the electrodes.

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8
Q

inner working of galvanic (volataic) cells

A

two separate compartments that contain one or the other of the electrodes.

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9
Q

another name for voltaic cell

A

galvanic

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10
Q

electrolyte solution

A

aqueous solution that surrounds the electrodes and consists of cations and anions.

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11
Q

Galvanic cell: daniel cell

A

the cations in the two half-cell solutions can be of the same element as the respective metal electrodes.

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12
Q

Galvanic cell: salt bridge

A

connects the two solutions and contains an inert salt.
 Permits the exchange of cations and anions and dissipates the charge gradient.
 Anions flow to anion side and cations flow to cation side.

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13
Q

Galvanic cell: As the spontaneous reaction proceeds toward equilibrium, the movement of electrons results in a conversion of _____

A

electrical potential energy into kinetic energy

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14
Q

if the two reactions in a galvanic cell were not separated, what would happen?

A

o If the two half-reactions were not separated then no work could be done.

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15
Q

cell diagram

A

: shorthand notation representing the reactions in an electrochemical cell.
o Rules for writing it out (see equations sheet)

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16
Q

what is similar between electrolytic and galvanic cells?

A

 All electrochemical cells have oxidation at anode and reduction at cathode.
 Electron flow from anode to cathode
 Current flow from cathode to anode.

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17
Q

what is different between electrolytic and galvanic cells?

A

 House nonspontaneous reactions that require the input of energy to proceed.
 DeltaG>0

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18
Q

electrolysis

A

oxidation-reduction reaction driven by an external voltage source; chemical compounds are decomposed.

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19
Q

do the half-reactions needed to be separated in electrolytic cells?

A

 The half-reactions do not need to be separated into different compartments because the desired reaction is nonspontaneous. `

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20
Q

Faraday

A

the amount of chemical change induced in an electrolytic cell is directly proportional to the number of moles of electrons that are exchanged during the oxidation-reduction reaction.
• Mn+ +ne-  M(s)

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21
Q

what is faraday’s constant

A

10^5. amount of charge in one mole of electrons

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22
Q

how does a concentration cell compare to a galvanic cell?

A

o Similar:
 Contains two half-cells connected by a conductive material, allowing a spontaneous oxidation-reduction reaction to proceed, which generates a current and delivers energy.
o Different:
 Both of the electrodes are chemically identical and so current is generated as a function of a concentration gradient established between the two solutions surrounding the electrodes.
 When the concentrations are equal, the voltage is 0.
 The voltage can be calculated with the Nernst equation.
o Bio: represented by the cell membrane of a neuron.
 Resting membrane potential (Vm) created
• If the potential is sufficiently large, it will result in the firing of an action potential.

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23
Q

where do electrons move in concentration cell?

A

move to get equilibrium of ion gradient

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24
Q

rechargeable battery or cell

A

one that can function as both a galvanic and electrolytic cell.

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25
Q

lead-acid battery

A

specific type of rechargeable battery.
 When charged: Pb anode and porous PbO2 cathode connected with concentration H2SO4
 When discharged: two PbSO4 electroplated lead electrodes connected with dilute H2SO4
 The electric potential is positive
 Charging: the lead-acid cell is part of an electrolytic circuit.
• Just opposite, reverses the electroplating to create a concentrated H2SO4 solution again.

low energy density (produce power as function of weight)

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26
Q

nickel-cadmium battery

A

 Consist of two half cells made of solid cadmium (anode) and nickel (III) oxide-hydroxide (the cathode) connected by conductive KOH.
 Higher energy-density than lead-acid batteries.
 Provide higher surge currents: periods of large current early in the discharge cycle.
 Recently been replaced with nickel-metal hydride (NiMH) batteries

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27
Q

energy density

A

a measure of a battery’s ability to produce power as a function of its weight

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28
Q

do nickel-cadmium batteries or lead-acid batteries have higher energy density?

A

nick-cadmium batteries

29
Q

electrode charge designation in galvanic cell

A

 In a galvanic cell, current is spontaneously generated as electrons are released by the oxidized species at the anode and travel through the conductive material to the cathode, where reduction takes place.
• Anode is considered negative, so electrons move from negative (low electrical potential) to positive (high electric potential)

30
Q

Isoelectric focusing

A

technique used to separate amino acids or polypeptides based on their isoelectric points (pI).
 Positive charged (cations) will migrate toward cathode
 Negative charged (anions) will migrate toward anode.

31
Q

how are reduction potentials determined?

A

o Determined experimentally using the tendency of hydrogen ion (H+) to be reduced as an arbitrary zero reference point.

o A reduction potential is measured in V volts and defined relative to the standard hydrogen electrode (SHE), which is given a potential of 0 V by convention.

32
Q

when manipulating reduction potential:

A

flip sign but do not multiply

33
Q

the more positive the reduction potential, ___

A

the more likely it will be reduced

34
Q

reduction potential

A

: the tendency of a species to gain electrons and to be reduced.

35
Q

standard reduction potential

A

measured under standard conditions: 298K, 1 atm pressure, 1 M concentrations.

36
Q

reduction potential and galvanic cells

A

o For galvanic cells, the electrode with the more positive reduction potential is the cathode, and the electrode with the less positive reduction potential is the anode.

37
Q

reduction potential and electrolytic cells

A

o For electrolytic cells, the electrode with the more positive reduction potential is forced by the external voltage to be oxidized and is therefore the anode.

38
Q

electromotive force

A

o Standard electromotive force (emf or E°cell): the difference in potential (voltage) between two half-cells under standard conditions.
 Calculated using standard reduction potentials.

39
Q

when deviating from standard conditions what equation is used?

A

nernst equation

40
Q

____ cells and ____ cells house spontaneous reactions

A

galvanic and concentration

41
Q

In ALL electrochemical cells, oxidation occurs at the _____ and reduction occurs at the _____

A

anode

cathode

42
Q

if the emf is positive then it _____

A

releases energy, deltaG > 0

43
Q

for all electrochemical cells, the electrons move from ____ to ____ and the current runs from ____ to _____

A

anode to cathode

cathode to anode

44
Q

the free energy change and electromotive force always have ____ signs

A

opposite

45
Q

batteries are common ____ cells

A

galvanic

46
Q

the salt bridge consists of an ____ salt and is responsible for _____ of the charge gradient

A

inert

dissipation

47
Q

plating or galvanization

A

when the material is plated onto the cathode

48
Q

from the salt bridge, the anions flow toward where and the cations flow toward where?

A

anions to anode and cations to cathode

49
Q

electrolytic cells house _____ reactions that require ____ to proceed

A

nonspontaneous

energy

50
Q

one faraday is equal to _____

A

the amount of charge contained in one mole of electrons

1 F = 96485 C (which can be rounded up to 10^5)

51
Q

in a concentration cell, the current will stop when _______

A

the concentration of ionic species in the half-cells are equal.

52
Q

how can the voltage for concentration cells be calculated?

A

using the Nernst equation

53
Q

what type of cell has some of the lowest energy-to weight ratios?

A

lead-acid batteries

54
Q

surge current

A

periods of large current (amperage) early in the discharge cycle.

55
Q

charge designations for galvanic vs. electrolytic cells

A

galvanic:
- anode: negative
- cathode: positive
electrolytic:
- anode: + (the positive side of the battery or external source is connected to it)
- cathode: -

56
Q

in all electrochemical cells, ____ are attracted to the anode and ____ are attracted to the cathode

A

anions

cations

57
Q

in isoelectric focusing, positively charged amino acids will migrate ____ and negatively charged amino acids will migrate ____

A

toward the cathode

to the anode

58
Q

In Molten NaCl cells, the electrodes consist of ____

A

anything as long as it can resist high temperatures and the corrosion

59
Q

what is at the anode and cathode for charging and discharging lead-acid batteries and Ni-Cd batteries?

A

NiCd

  • Discharging: Anode: Cd Cathode: NiO(OH)
  • Charging: Anode: Cd(OH)2 Cathode: Ni(OH)2

Lead acid

  • Discharging: Anode: Pb, Cathode: PbO2
  • Charging: PbSO4 for both
60
Q

what is the voltage of the standard hydrogen electrode?

A

0 V (SHE)

61
Q

reduction potential

A

the tendency of a species to gain electrons and to be reduced

62
Q

the more ____ the reduction potential, the greater the tendency to be reduced

A

positive

63
Q

oxidation potential is the same as reduction potential but _____

A

flipped sign

64
Q

the standard reduction potential of an electrode will not change unless the ____

A

chemical identity of that electrode is changed

is not multiplied by moles

65
Q

is the standard reduction potential multiplies by moles?

A

no

66
Q

galvanic cells have a ____ emf

A

positive

67
Q

potentiometer

A

a kind of voltmeter that draws no current and gives a more accurate reading of the difference in potential between two electrodes

68
Q

why have nickel-metal hydride (NiMH) batteries replaced Ni-Cd batteries?

A

they have a larger energy density, are more cost effective, and are significantly less toxic.

69
Q

E cell is dependent only on the ____ of electrodes and not the ____

A 
identity 
amount present (size or mass)

MCAT Chem (12 decks)

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