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MCAT Chem > Chem #10 > Flashcards

Chem #10 Flashcards

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1
Q

what makes a stronger base

A

a stronger base has more EDG that would be able to stabilize a positive charge when a hydrogen is added

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2
Q

what does the Arrhenius definition of acids and bases refer to?

A

dissociation to form H+ or OH- ions

o Typically limited to aqueous acids and bases
o Very restrictive

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3
Q

Arrhenius acid

A

will dissociate to form an excess of H+ in solution

 Have H at the beginning of their chemical name.

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4
Q

Arrhenius base

A

will dissociate to form an excess of OH- in solution

 Have OH at the end of their chemical name.

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5
Q

what does the Bronsted-Lowry definition of acids and bases refer to?

A

donating or accepting H+

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6
Q

Bronsted-Lowry Acid

A

a species that donates H+

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7
Q

Bronsted-Lowry base

A

: a species that accepts H+

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8
Q

conjugate acid/base pairs

A

transfer of a proton from acid to base.

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9
Q

what does the Lewis definition of acids and bases refer to?

A

donating or accepting an electron pair

o Also known as coordinate covalent bond formation, complex ion formation, or nucleophile-electrophile interactions.

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10
Q

lewis acid

A

an electron pair acceptor

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11
Q

lewis base

A

electron pair donator

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12
Q

amphoteric species

A

one that reacs like an acid in a basic environment and like a base in an acidic environment.
o Amphiprotic: can gain or lose a proton.
o Ex: H2O and HSO4-
o Also species that can accept or donate electrons.

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13
Q

autoionization of water

A

water can react with itself.
 For pure water at 298 K, the water dissociation constant Kw = 10-14
• Kw is only affected by temperature, not concentration, pressure, or volume changes.

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14
Q

lower pH is ___

A

acidic

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15
Q

higher pH is ___

A

basic

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16
Q

strong acids and bases

A

completely dissociate into their component ions in aqueous solutions.
o Contribution of ionization of water is only important if the concentration of the strong acid or base is near 10-7.

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17
Q

weak acids and bases

A

only partially dissociate in aqueous solutions, and the less it will dissociate.

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18
Q

acid dissociation constant

A

 Acid dissociation constant, Ka

• The smaller the Ka, the weaker the acid.

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19
Q

base dissociation constant

A

 Base dissociation constant, Kb

• The smaller the Kb, the weaker the base, and the less it will dissociate.

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20
Q

conjugate acid

A

the acid formed when a base gains a proton

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21
Q

conjugate base

A

the base formed when an acid loses a proton.

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22
Q

a strong acid has a ____ conjugate base

A

weak

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23
Q

EWG near an H on an acid _____ its acidic capabailities

A

increase

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24
Q

polyvalent

A

each mole of the acid or base liberates more than one acid or base equivalent.

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25
Q

2 M of H3PO4 has a normality of ____

A

6

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26
Q

titration

A

a procedure to determine the concentration of a known reactant in solution.

o Titrations are performed by adding small volumes of a solution of known concentration (titrant) to a known volume of a solution of unknown concentration (titrand) until completion of the reaction is achieved at the equivalence point.

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27
Q

titrant

A

gets added

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28
Q

titrand

A

added to (usually trying to find out its concentration)

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29
Q

indicator

A

weak organic acids or bases that have different colors in their protonated or deprotonated states.
o Used in low concentrations to not alter the equivalence point.
o Endpoint: the point at which the indicator changes to its final color.
o If the indicator is picked well and the titration is done right, the volume difference between the endpoint and the equivalence point is negligible.

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30
Q

endpoint

A

o Endpoint: the point at which the indicator changes to its final color.

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31
Q

how should the indicator be selected?

A

Select the indicator that has the closest pKa value to the equivalence point.

Should be chosen closest to the endpoint

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32
Q

describe the titration: strong acid with strong base

A

o Equivalence point is 7
o The acid dominates at low addition of strong base and the base dominates after the endpoint.
o Drastic change in the middle.
o Equivalence point using a pH meter is the midpoint region of the curve with the steepest slope.

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33
Q

describe the titration: weak acid with strong base

A

o Equivalence point >7
o The initial pH is greater than for the strong acid starting solution ^^
o The pH changes gradually early on and has a less sudden rise at the equivalence point.

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34
Q

describe the titration: strong acid with weak base

A

o Equivalence point <7
o Initial pH is in the basic range.
o Gradual decrease in pH and once again not as steep of a slope as in the strong-strong condition.

35
Q

describe the titration: weak acid with weak base

A

o Equivalence point near pH 7

o Very gradual equivalence point

36
Q

titration curve for polyvalent acids and bases

A

o Have two buffer regions, half equivalence points and equivalence points
o Acidic or basic amino acids have 3 equivalence points

37
Q

half equivalence point

A

when half of the given species has been protonated or deprotonated.

when the acid = conjugate base and vice versa

38
Q

half equivalence point

A

when half of the given species has been protonated or deprotonated.

when the acid = conjugate base and vice versa

39
Q

buffer solution

A

consists of a mixture of a weak acid and its salt or a weak base and its salt.
o Resist changes in pH when small amounts of acid or base are added.
o The Bicarbonate Buffer system
 H2CO3/HCO3- conjugate pair in the blood
 Acidosis, breath heavier, blow out more CO2, shift left and reduce H+ in blood.

40
Q

henderson hasselbach equation

A

used to estimate the pH or pOH of a buffer solution.
o [HA] = [A-], pH = pKa, buffer is at its best
o Buffering capacity: the ability to which the system can resist changes in pH
 Doubles if concentrations are double for the conjugate pairs.

41
Q

every arhenius acid or base is a ______ acid and base

A

bronsted lowry (but not other way around)

42
Q

every bronsted lowry acid or base is a ____ acid or base

A

lewis

43
Q

amphoteric vs. amphiprotic

A

amphoteric: acts like an acid or base depending on the environment
amphiprotic: can gain or give away a proton

44
Q

zwitterions have both ______ character

A

anionic and cationic

45
Q

HClO

A

hypochlorous acid

46
Q

HClO2

A

chlorous acid

47
Q

HClO3

A

chloric acid

48
Q

HClO4

A

perchloric acid

49
Q

HNO2

A

nitrous acid

50
Q

HNO3

A

nitric acid

51
Q

H3BO3

A

Boric acid

52
Q

H2CrO4

A

chromic acid

53
Q

a ____ is never isolated in solution as it is always attached to water or some other species that has the ability to accept it

A

H+

54
Q

the value of Kw changes at different _____

A

temperatures

Changing pressure, volume, and concentration will not change the Kw.

55
Q

is the autoionization reaction endothermic or exothermic?

A

endothermic

56
Q

what is a p scale?

A

a p scale is defined as the negtive logarithm of the number of items.

57
Q

pH + pOH = 14 only holds at _____

A

298 K (because that is when the kw = 10^-14)

58
Q

a pH of 1 is ____ while a pH of 10 is ____

A

acidic

basic

59
Q

if the concentration of an acid or base is close to 10^-7, then the contribution from ______ is important to consider

A

the autoionization of water

if they are greater than 10^-7, then don’t worry about it.

60
Q

what are the strong acids?

A

HCl, HBr, HI, H2SO4, HNO3, HClO4

61
Q

does the pH scale go past 0 and 14?

A

yes, at very strong or very basic solutions.

62
Q

a strong acid _____ dissociates to produce a ____ solution

A

completely

concentrated (as opposed to dilute)

63
Q

a Ka or Kb value less than ____ is considered for a weak acid or base

A

1

64
Q

Kw = what?

A

multiplying the Ka and Kb for an acid and conjugate base or base and conjugate acid
MUST BE CONJUGATE ACID/BASE PAIRS

65
Q

a strong acid will produce a ____ conjugate base

A

weak (based on Ka x Kb = Kw)

66
Q

acids that have ______ elements nearer to acidic hydrogens are stronger than those that do not

A

electronegative

67
Q

explain the assumptions when doing problems that deal with Ka or Kb

A

the assumption is that the value of x (how much acid or base is dissociating) is less than 5% of the original concentration of acid or base. This is oftentimes true when the Ka is 100 times less than the concentration of the starting solution.

68
Q

the pH of a reaction between a strong base and weak acid is ____ and the pH of a reaction between a strong acid and a weak base is

A

basic (above 7)

acidic (below 7)

69
Q

What is the normality of a 2M solution of H3PO4

A

6 N

70
Q

Typically, we know the concentration of the ____ but not the ____ in a titration

A

titrant

titrand

71
Q

what are the units for normality?

A

equivalence per volume

72
Q

______ are weak organic acids or bases that have different colors in their protonated and deprotonated states.

A

indicators.

73
Q

the indicator must always be _____ than the acid or base being titrated

A

a weaker acid or base

74
Q

the point at which the indicator changes to its final color is not the equivalence point but rather the ____

A

endpoint

75
Q

the indicator has a ___ value very close to the _____ of the equivalence point

A

pKa

pH

76
Q

If I am titrating HCl with NaOH, which is the titrant and which is the titrand

A

titrant is NaOH and titrand is HCl

77
Q

What are 3 differences between the titration curve for strong acids/strong bases and weak acids/strong bases

A
  1. the initial pH of the acidic solution is higher because it is a weak acid
  2. the slope of the curve is greater at first and the slope at the equivalence point is not as steep
  3. the equivalence point is greater than 7 (due to the presence of the strong base with a weak acid).
78
Q

amino acids with acidic or basic side chains have _____ equivalence points

A

3

79
Q

____ solutions have the useful property of resisting changes in pH when small amounts of acid or base are added

A

buffer

80
Q

buffers work by ____

A

shifting the reaction to form either more of the weak acid or weak base which does not have an effect on the pH.

81
Q

what is the range of optimal activity for buffers?

A

+/- 1 the pKa

82
Q

what equation is used to estimate the pH or the pKa of a buffer solution?

A

the henderson hasselbach equation

83
Q

a weak acid and weak base titration combo will have an equivalence point where?

A

depends on the relative strengths of the acid and base

84
Q

If given the concentration of H2SO4, the concentration of H3O+ is ____ this concentration

A

double, because it has 2 H+ ions to donate

MCAT Chem (12 decks)

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