Chemistry - MCAT Flashcards
1
Q
Does raising the temperature of a reaction shift equilibrium towards the products or reactants?
A
products
2
Q
If you feel heat outside of a reaction vessel, is it endo or exothermic?
A
exothermic
3
Q
What is the enthalpy of O2?
A
0
4
Q
If Q>Keq, will the reaction need to proceed towards the products or reactants?
A
reactants
5
Q
A Keq>1 is associated with a negative or positive Gibbs free energy?
A
negative
6
Q
If between two reactions one has a lower Ea but less stable product, will it be kinetically or thermodynamically favored?
A
kinetically
7
Q
What is the charge on a strong electrophile?
A
positive
8
Q
What feature do nucleophiles have?
A
pair of electrons to share/donate
9
Q
What charge is on a weak nucleophile?
A
neutral
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
11
Q
Does an SN1 reaction depend on the concentration of one or two reactants?
A
one
12
Q
What type of substitution reaction results in a racemic mixture?
A
SN1
13
Q
Are unstable atoms/molecules (such as more E.N.) better leaving groups than stable ones?
A
yes
14
Q
Do SN1 reactions favor a more or less substituted carbocation?
A
more (3* and 2* carbocations)
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
16
Q
When the reagent is a less substituted carbon, will an SN1 or SN2 reaction be favored?
A
SN2
17
Q
What type of solvent favors SN2 reactions?
A
polar aprotic (can NOT form H bonds)
18
Q
Does a strong nucleophile indicate an SN1 or SN2 reaction?
A
SN2
19
Q
What type of molecule makes the best leaving group?
A
weak base
20
Q
What is the rate law for an E1 or SN1 reaction?
A
rate=k{A}
21
Q
A bronsted base is defined by what?
A
Proton Acceptance
22
Q
What is the rate law for SN2 and E2 reactions?
A
rate=k{A}{B}
23
Q
Do elimination reactions prefer more or less substituted carbocations?
A
more
24
Q
What states of compounds are included in the Keq equation?
A
gaseous and aqueous species
25
If volume decreases, which way will the reaction shift?
note: it is to maintain pressure
Towards the side with fewer *mols* of gas to decrease the pressure exerted on the container
26
What is the effect on equilibrium if you add an *inert gas* to the reaction?
No effect - total pressure of vessel increases but partial pressures remain the same
27
How does equilibrium shift if temperature increases?
shifts towards endothermic side
| if endothermic rxn - towards products; if exothermic rxn - towards reactants
28
If Q
reactants
29
If the concentration of reactants increases, what way will the reaction shift to compensate and reestablish equilibrium?
towards products
30
What compounds are NOT soluble?
carbonates, phosphates, sulfides, and sulfites UNLESS bound to alkali metal
31
What compounds are soluble?
nitrates, chlorates, acetates, sulfates, alkali metals (except calcium, Sr, Ba), Halides,(except silver, lead, mercury)
32
What does molality (m) measure?
moles of solute / kg solvent
33
What does normality (N) measure?
equivalents reactive species / L solution
equation:
molarity of acid * acidic protons/molecule
34
What state of molecules are included in the Ksp calculation?
aqueous only!
35
A high Ksp value means what?
Compound dissolves readily (high conc. of dissolved compounds)
36
A Ksp<1 signifies what?
An insoluble compound
37
What are the two equations for Ksp?
Ksp = [aq products] / [aq reactants]
OR
Ksp=[cation][anion]
38
Adding a common ion to a solution in which the dissolving compound is still being dissolved will do what to its solubility?
decrease it
| common ion effect but explained by Le Chatlier's principle
39
Can pH affect the solubility of a compound?
Yes! If that compound contains H/OH, the common ion effect will occur (decrease in pH=increase in H+=reduction in solubility)
40
How do you calculate for Kw?
=[H3O+][OH-]
41
What types of acids have *strong* conjugate bases?
weak!
note: a higher pKa
42
A high Ka corresponds to a ____ acid while a high pKa corresponds to a ____ acid
strong, weak
43
What is an amphoretic molecule?
One that can act as both an acid and base
44
What is the Bronsted Lowry definition for acids and bases respectively?
proton donor
| proton acceptor
45
What is the Lewis acid and base definitions respectively?
electron acceptor
| electron donor
46
What is the Arrhenius acid and base definitions respectively?
dissociates to form H+
| dissociates to form OH-
47
What happens when pH=pKa?
There are equal amounts of protonated and deprotonated acid/base
48
At physiological pH, what is the charge on the C terminus and N terminus respectively?
C -1 (pKa ~2)
| N +1 (pKa ~10)
49
If you titrate a strong acid with a weak base, what should the pH of your indicator be?
less than 7 (equilibrium will be less than 7)
50
What state changes are exothermic?
liquid -> solid (freezing)
gas -> liquid (condensation)
gas->solid (deposition)
because they lose heat energy!!!!!
51
What is the spontaneity of a reaction that has a highly positive reduction potential?
It is spontaneous
52
If you have two half reactions with reduction potentials given, which species will be reduced and which will be oxidized?
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
What is the E* of a galvanic cell? note: always spontaneous!
positive
54
Which is reduced and which is oxidized between cathode and anode?
cathode is reduced
| anode is oxidized
55
In an electrolytic cell, what is the E* cell and spontaneity?
E* is negative; non-spontaneous (requires external energy)
56
What is on the anode and cathode of an electrolytic cell respectively?
Oxygen - gets oxidized
| Hydrogen - gets reduced
57
What is the pKa of an ideal buffer?
Within +/- 1 pH of the solution
58
In a titration, when does pH=pKa? i.e. acid and base conc. are equal
half-equivalence point
59
What type of molecule shows color when synthesized?
fully conjugated molecule (alternating double-bonds) and transition metals (d orbitals)
60
What types of interactions form surface tension?
inTERmolecular forces
61
Is CO2 polar?
NO - IT IS LINEAR NOT BEND
62
What changes due to gamma decay?
Nucleus goes from high energy to low energy state by emission of electromagnetic radiation
63
What are the products of Beta minus decay?
Neutron -> proton
| Emits electron
64
What size of proteins travels farthest in an electrophoresis gel?
small proteins
65
What does PCR analyze?
DNA amplification (RT-PCR looks at mRNA)
66
What does SDS Page separate?
proteins by mass
67
What is the coordination number of an atom in a molecule?
The number of ligands attached to it
68
What causes something to distill?
```
It reaches its boiling point
intermolecular forces (H bonding, etc), molecular weight can cause increased boiling point
```
69
What elutes first in cation-exchange chromatography?
Negative molecules (positive are trapped to the sides)
70
What elutes first in anion exchange chromatography?
Positive molecules (negative ones are trapped on the sides)
71
How does column chromatography work?
Ligands that are specific for the molecule of interest are added as the stationary phase so they elute last
72
In gas-liquid chromatography, what does the first peak represent?
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
List the light spectrum in order of lowest wavelength to greatest
Gamma rays, X rays, UV rays, Visual light, IR, microwaves, Radio waves
74
What can IR spectrospy detect?
Polar covalent bonds
75
When analyzing using UV-Vis spectroscopy, what do the peaks represent?
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
What is a requirement of NMR?
There is a net spin (uneven number of protons or neutrons)
77
Where are polar compounds found on NMR?
downfield / unshielded due to electronegativity (pulls away from Carbon/Hydrogen and causes them to gain a net spin)
78
Where are non-polar compounds found on NMR?
upfield / shielded due to lack of electronegativity
79
What shows up on H-NMR as a peak?
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
What does the furthest right peak represent in mass spectroscopy?
The "parent" peak (M+ ion) or full molecule; x-axis is mass/charge
81
What is the tallest peak in mass spectroscopy?
the "base" peak or ion that is most abundant
82
In SDS-Page, what protein travels the fartherst?
lowest weight
83
What causes inhibition in a PCR?
ddNTPs (dNTPS are normal)
84
What elutes first in gas chromatography?
molecule with lower boiling point (typically non-polar)
85
What type of cell is used for electrophoresis and what does this mean in regards to the charge and direction of the protein?
electrolytic cell
| protein will be negatively charged and move towards the anode (which is positively charged)
86
When is vacuum distillation used vs fractional distillation?
vacuum distillation - very HIGH boiling points
| fractional distillations - isolating two CLOSE boiling points (<25 deg C difference)
