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MCAT > Chemistry - MCAT > Flashcards

Chemistry - MCAT Flashcards

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MCAT flashcards
1
Q

Does raising the temperature of a reaction shift equilibrium towards the products or reactants?

A

products

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2
Q

If you feel heat outside of a reaction vessel, is it endo or exothermic?

A

exothermic

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3
Q

What is the enthalpy of O2?

A

0

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4
Q

If Q>Keq, will the reaction need to proceed towards the products or reactants?

A

reactants

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5
Q

A Keq>1 is associated with a negative or positive Gibbs free energy?

A

negative

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6
Q

If between two reactions one has a lower Ea but less stable product, will it be kinetically or thermodynamically favored?

A

kinetically

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7
Q

What is the charge on a strong electrophile?

A

positive

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8
Q

What feature do nucleophiles have?

A

pair of electrons to share/donate

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9
Q

What charge is on a weak nucleophile?

A

neutral

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10
Q

Ammonia is an example of what type of nucleophile due to the fact that the Nitrogen is not very E.N. (doesn’t hold the lone pair very tight)?

A

strong

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11
Q

Does an SN1 reaction depend on the concentration of one or two reactants?

A

one

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12
Q

What type of substitution reaction results in a racemic mixture?

A

SN1

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13
Q

Are unstable atoms/molecules (such as more E.N.) better leaving groups than stable ones?

A

yes

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14
Q

Do SN1 reactions favor a more or less substituted carbocation?

A

more (3* and 2* carbocations)

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15
Q

What type of solvent favors an SN1 reaction?

A

polar protic (can form H bonds, highly E.N.) bc it will surround the L.G. so it doesn’t react again

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16
Q

When the reagent is a less substituted carbon, will an SN1 or SN2 reaction be favored?

A

SN2

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17
Q

What type of solvent favors SN2 reactions?

A

polar aprotic (can NOT form H bonds)

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18
Q

Does a strong nucleophile indicate an SN1 or SN2 reaction?

A

SN2

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19
Q

What type of molecule makes the best leaving group?

A

weak base

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20
Q

What is the rate law for an E1 or SN1 reaction?

A

rate=k{A}

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21
Q

A bronsted base is defined by what?

A

Proton Acceptance

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22
Q

What is the rate law for SN2 and E2 reactions?

A

rate=k{A}{B}

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23
Q

Do elimination reactions prefer more or less substituted carbocations?

A

more

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24
Q

What states of compounds are included in the Keq equation?

A

gaseous and aqueous species

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25
Q

If volume decreases, which way will the reaction shift?

note: it is to maintain pressure

A

Towards the side with fewer mols of gas to decrease the pressure exerted on the container

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26
Q

What is the effect on equilibrium if you add an inert gas to the reaction?

A

No effect - total pressure of vessel increases but partial pressures remain the same

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27
Q

How does equilibrium shift if temperature increases?

A

shifts towards endothermic side

if endothermic rxn - towards products; if exothermic rxn - towards reactants

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28
Q

If Q

A

reactants

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29
Q

If the concentration of reactants increases, what way will the reaction shift to compensate and reestablish equilibrium?

A

towards products

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30
Q

What compounds are NOT soluble?

A

carbonates, phosphates, sulfides, and sulfites UNLESS bound to alkali metal

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31
Q

What compounds are soluble?

A

nitrates, chlorates, acetates, sulfates, alkali metals (except calcium, Sr, Ba), Halides,(except silver, lead, mercury)

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32
Q

What does molality (m) measure?

A

moles of solute / kg solvent

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33
Q

What does normality (N) measure?

A

equivalents reactive species / L solution

equation:
molarity of acid * acidic protons/molecule

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34
Q

What state of molecules are included in the Ksp calculation?

A

aqueous only!

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35
Q

A high Ksp value means what?

A

Compound dissolves readily (high conc. of dissolved compounds)

36
Q

A Ksp<1 signifies what?

A

An insoluble compound

37
Q

What are the two equations for Ksp?

A

Ksp = [aq products] / [aq reactants]

OR

Ksp=[cation][anion]

38
Q

Adding a common ion to a solution in which the dissolving compound is still being dissolved will do what to its solubility?

A

decrease it

common ion effect but explained by Le Chatlier’s principle

39
Q

Can pH affect the solubility of a compound?

A

Yes! If that compound contains H/OH, the common ion effect will occur (decrease in pH=increase in H+=reduction in solubility)

40
Q

How do you calculate for Kw?

A

=[H3O+][OH-]

41
Q

What types of acids have strong conjugate bases?

A

weak!

note: a higher pKa

42
Q

A high Ka corresponds to a ____ acid while a high pKa corresponds to a ____ acid

A

strong, weak

43
Q

What is an amphoretic molecule?

A

One that can act as both an acid and base

44
Q

What is the Bronsted Lowry definition for acids and bases respectively?

A

proton donor

proton acceptor

45
Q

What is the Lewis acid and base definitions respectively?

A

electron acceptor

electron donor

46
Q

What is the Arrhenius acid and base definitions respectively?

A

dissociates to form H+

dissociates to form OH-

47
Q

What happens when pH=pKa?

A

There are equal amounts of protonated and deprotonated acid/base

48
Q

At physiological pH, what is the charge on the C terminus and N terminus respectively?

A

C -1 (pKa ~2)

N +1 (pKa ~10)

49
Q

If you titrate a strong acid with a weak base, what should the pH of your indicator be?

A

less than 7 (equilibrium will be less than 7)

50
Q

What state changes are exothermic?

A

liquid -> solid (freezing)
gas -> liquid (condensation)
gas->solid (deposition)

because they lose heat energy!!!!!

51
Q

What is the spontaneity of a reaction that has a highly positive reduction potential?

A

It is spontaneous

52
Q

If you have two half reactions with reduction potentials given, which species will be reduced and which will be oxidized?

A

the larger reduction potential will get reduced and the other will be oxidized BUT you have to reverse the sign of the oxidized molecule’s reduction potential to get the oxidation potential

note: more moles of substance does NOT change the magnitude of the ox/red potential

53
Q

What is the E* of a galvanic cell? note: always spontaneous!

A

positive

54
Q

Which is reduced and which is oxidized between cathode and anode?

A

cathode is reduced

anode is oxidized

55
Q

In an electrolytic cell, what is the E* cell and spontaneity?

A

E* is negative; non-spontaneous (requires external energy)

56
Q

What is on the anode and cathode of an electrolytic cell respectively?

A

Oxygen - gets oxidized

Hydrogen - gets reduced

57
Q

What is the pKa of an ideal buffer?

A

Within +/- 1 pH of the solution

58
Q

In a titration, when does pH=pKa? i.e. acid and base conc. are equal

A

half-equivalence point

59
Q

What type of molecule shows color when synthesized?

A

fully conjugated molecule (alternating double-bonds) and transition metals (d orbitals)

60
Q

What types of interactions form surface tension?

A

inTERmolecular forces

61
Q

Is CO2 polar?

A

NO - IT IS LINEAR NOT BEND

62
Q

What changes due to gamma decay?

A

Nucleus goes from high energy to low energy state by emission of electromagnetic radiation

63
Q

What are the products of Beta minus decay?

A

Neutron -> proton

Emits electron

64
Q

What size of proteins travels farthest in an electrophoresis gel?

A

small proteins

65
Q

What does PCR analyze?

A

DNA amplification (RT-PCR looks at mRNA)

66
Q

What does SDS Page separate?

A

proteins by mass

67
Q

What is the coordination number of an atom in a molecule?

A

The number of ligands attached to it

68
Q

What causes something to distill?

A 
It reaches its boiling point
intermolecular forces (H bonding, etc), molecular weight can cause increased boiling point
69
Q

What elutes first in cation-exchange chromatography?

A

Negative molecules (positive are trapped to the sides)

70
Q

What elutes first in anion exchange chromatography?

A

Positive molecules (negative ones are trapped on the sides)

71
Q

How does column chromatography work?

A

Ligands that are specific for the molecule of interest are added as the stationary phase so they elute last

72
Q

In gas-liquid chromatography, what does the first peak represent?

A

The first chemical eluted (typically lowest BP, but could have to do with polarity and its reaction with the solvent/eluent)

normal: non-polar elutes first
reverse phase: polar elutes first

73
Q

List the light spectrum in order of lowest wavelength to greatest

A

Gamma rays, X rays, UV rays, Visual light, IR, microwaves, Radio waves

74
Q

What can IR spectrospy detect?

A

Polar covalent bonds

75
Q

When analyzing using UV-Vis spectroscopy, what do the peaks represent?

A

The light that was absorbed by the compound NOT REFLECTED (i.e. it will absorb the colors that it is NOT and reflect the colors that it is)

76
Q

What is a requirement of NMR?

A

There is a net spin (uneven number of protons or neutrons)

77
Q

Where are polar compounds found on NMR?

A

downfield / unshielded due to electronegativity (pulls away from Carbon/Hydrogen and causes them to gain a net spin)

78
Q

Where are non-polar compounds found on NMR?

A

upfield / shielded due to lack of electronegativity

79
Q

What shows up on H-NMR as a peak?

A

Each DIFFERENT group of hydrogens (ex. a CH3 group is all chemically equivalent)…the more shielded or close to electron withdrawing group they are, the further downfield they are, area under the peak is number of hydrogens in group, number of peaks in group is number of carbons adjacent +hydrogen

80
Q

What does the furthest right peak represent in mass spectroscopy?

A

The “parent” peak (M+ ion) or full molecule; x-axis is mass/charge

81
Q

What is the tallest peak in mass spectroscopy?

A

the “base” peak or ion that is most abundant

82
Q

In SDS-Page, what protein travels the fartherst?

A

lowest weight

83
Q

What causes inhibition in a PCR?

A

ddNTPs (dNTPS are normal)

84
Q

What elutes first in gas chromatography?

A

molecule with lower boiling point (typically non-polar)

85
Q

What type of cell is used for electrophoresis and what does this mean in regards to the charge and direction of the protein?

A

electrolytic cell

protein will be negatively charged and move towards the anode (which is positively charged)

86
Q

When is vacuum distillation used vs fractional distillation?

A

vacuum distillation - very HIGH boiling points

fractional distillations - isolating two CLOSE boiling points (<25 deg C difference)

MCAT (6 decks)

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