MCAT General Chemistry-Acids and Bases

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1

acids: create H+ in solution
bases: creates OH- in solution

Arrhenius Definition of acids and bases

2

Lewis acids: electron pair acceptor
Lewis base: electron pair donor

Lewis Definition of acids and bases

3

Acids: proton donors
Bases: proton acceptors

Bronsted-Lowry Definition of acids and bases

4

Conjugate base

structure after BL-acid donates a proton

5

Conjugate acid

structure after BL-base accepts a proton

6

Strong acid

acid that completely dissociates in solution

7

weak acid

acid that does not completely dissociate in H₂O

8

acid-ionization constant (Ka)

equilibrium for acid dissociation that indicates strength of the acid
Ka=[H₃O][A⁻]/[HA]
NOTE: the larger the Ka, the stronger the acid

9

Products are favored, and the acid is a strong acid

Acid-ionization constant>1 indicates what about the rxn?

10

Reactants are favored and the acid is weak

Acid-ionization constant <1 indicates what about the rxn?

11

HI, HBr, HCl, HClO₄, H₂SO₄, HNO₃, and HSO₄⁻

List of strong acid (Ka>1)

12

Base ionization constant (Kb)

equilibrium for base dissociation that indicates strength of the base
Kb=[HB][OH⁻]/[B]
NOTE: the larger the Kb, the stronger the base

13

OH⁻, OR⁻, NH₂⁻, NR₂⁻, H⁻, R⁻, O²⁻

List of strong bases

14

a conjugate base of a strong acid has NO basic properties in H₂O

Conjugate base of strong acid in H₂O

15

will be more basic than water, and be able to accept protons and donate electrons

Conjugate base of weak acid in H₂O

16

the conjugate acid of a strong base has NO acidic properties (will not donate any protons)

Conjugate acid of a strong base in H₂O

17

the conjugate acid of a weak base has weak acidic properties
NOTE: the weaker the base, the stronger the conjugate acid

Conjugate acid of a weak base in H₂O

18

amphoteric substances

wherever a substance can act either as a base or an acid
Conjugate bases of polyprotic acids

19

Yes, it has two H+

Is H₂O amphoteric?

20

Autoionization

the self ionization of H₂O

21

Equilibrium Expression for autoionization of H₂O
Kw=1*10⁻¹⁴ at 25C

Kw=[H₃O][OH]
Only varied by temperature (like other equilibrium constants, increasing as temperature increases)

22

pH

measure of the concentration of H+ in solution

23

pH=-log[H+]
NOTE: log of 1=0

Formula for pH

24

pH<7 is acidic
pH=7 is neutral
pH>7 is basic

pH values determining acidity or basicity at STP

25

pOH

concentration of OH in solution

26

pOH=-log[OH⁻]

Formula for pOH

27

pOH+pH=14 at 25C

pOH+pH=?

28

strength of an acid or strength of a base. a compound cannot compare pka and pkb

Definitions of pKa and pKb

29

Ka*Kb=10⁻¹⁴ for conjugates only

Relationship between Ka and Kb

30

pKa+pKb=14

pKa+pkb=14 for conjugates only

31

strong acids dissociate completely, therefore the concentration of H+ is equal to the concentration of the acid

pH calculations w/ strong acids gives what value for the concentration of products?

32

weak acids come to equilibrium w/ dissociated ions
Ka=[H][A-]/[HA]=x²/([original con HA]-x)

Ka calculations for weak acids gives what value for the concentration of products?

33

K<10⁻⁴

When can X in the denominator for Ka equation be considered negligible?

34

Neutralization rxn

when an acid and a base combine to produce salt and H₂O
NOTE: all (blank) rxns go to completion regardless of the strength of base or acid

35

a[A]Va=b[B]Vb

Neutralization Equation

36

Salt

ionic compound, consisting of a cation and an anion; in H₂O, (blank) dissociate into ions
NOTE: determines whether solution will be neutral, acidic, or basic

37

Group I cations and larger Group II cations

Which cations of a salt do not react w/ H₂O?

38

NH₄⁺, Be²⁺, Cu²⁺, Zn²⁺, Al³⁺, Cr³⁺, Fe³⁺

Cations that are stronger acids than H₂O

39

Anions that do not react w/ H₂O

conjugate bases of a strong acid

40

will be more basic than water and be able to donate electrons and accept protons

conjugate bases of weak acids

41

Hydrolysis rxn

rxn of a substance (salt or ion) w/ H₂O

42

Buffer Solution

Weak acid with conjugate base (or weak base with conjugate acid)
solution that resists changing pH when a small amount of acid or base is added

43

should match buffer pKa with buffered pH

Buffer choice should what?

44

Buffer capacity

presence of a weak acid and conjugate base in equal concentrations, or weak base and its conjugate acid

45

pH-pKa=log[A⁻]/[HA]

Henderson-Hasselbalch Equation (for acid)

46

pOH-pKb=log[HB]/[B]

Henderson-Hasselbalch Equation (for base)

47

Indicator

weak acid that undergoes a color change when its converted to its conjugate base

48

[H₃O⁺]/Ka=[HA]/[A⁻]

Equation for determining color of indicator

49

protonated form will dominate

If [H₃O]>>Ka, then....

50

the deprotonated form is dominant

If [H₃O]<<Ka, then....

51

both protonated and deprotonated forms will be present

If [H₃O]=Ka, then...

52

pKa +/- 1

Range of indicator end points

53

Acid-Base Titration

experimental technique to identify an unknown weak acid or base by determining its pKa or pKb

54

Titrant

strong acid or base added to solution containing the unknown
NOTE: (blank) of an acid is always a base and vice versa

55

Buffer Region

section of titration curve where pH changes gradually

56

Acid-base equivalent point

point where moles added equals moles of original solution, leaving solely neutral salt

57

The equivalence point of a weak acid

equivalence point will be at pH>7

58

The Equivalence point of a weak base

equivalence point will be at pH<7

59

Equivalence point of a strong acid w/ a strong base

equivalence point will occur at pH=7

60

Half Equivalence Point

point where half the volume of titrant is added as the equivalence point; where weak acid has equal concentration with conjugate base
***pH=pKa

61

Polyprotic Titrations

have more than one equivalence point due to increased number of hydrogens. With each equivalence point reached the Ka decreases

62

Polyprotic base

base that can accept two subsequent protons

63

Protonated indicator dominates

when pH<pKa, the solution is too acidic or has too many protons

64

Deprotonated form will dominate

when pH>pKa, what form will dominate?

65

pKa w/in 1 pH point of the pH to be indicated

When choosing an indicator, the pKa should w/in what value of the pH?

66

compound that differ by only one proton

What is a conjugate?

67

ClO₃⁻

formula for chlorate?

68

CO₃²⁻

formula for carbonate?

69

PO₄³⁻

formula for phosphate?

70

SO₄²⁻

formula for sulfate?

71

NO₃⁻

formula for nitrate?

72

Cl⁻

formula for chloride?

73

ClO⁻

formula for hypochlorate?

74

ClO₂⁻

formula for chlorite?

75

ClO₄⁻

formula for perichlorate?

76

CH₃COO⁻

formula for acetate?

77

C₆H₅COO⁻

formula for benzoate?

78

oxide, O²⁻

Which strong base is diprotic?

79

sulfuric acid, H₂SO₄

Which strong acid is diprotic?

80

HF, NH₄⁺, H₂CO₃, phenol, RCOOH, RNH₃⁺, Al³⁺, BF₃

List of useful weak acids?

81

Al³⁺ and BF₃

Which weak acids are lewis acids?

82

F⁻, NH₃, HCO₃⁻, phenol-O⁻, RCOO⁻, RNH₂, CN⁻

List of useful weak bases?

83

increase acidity through induction

Do electron withdrawing groups decrease or increase acidity?

84

decrease acidity by making it less likely to receive electrons

Do electron donating groups decrease or increase acidity?

85

lone pair of electrons

What must all bases have to donate electrons, and thus act like a base?

86

Nnnnnooooo. Only exception is conjugates

Can pKa and pKb be compared?

87

No this can be varied with temperature

Does the neutral pH always have to be 7?

88

pH=-log(2[H⁺])

What is the equation for calculating the pH of sulfuric acid?

89

pH=-1/2log(Ka[A])

What is the equation for calculating the pH using Ka and concentration of conjugate base?

90

pOH=-log(2[OH])

What is the equation for calculating the pOH of oxide?

91

Yes, the buffer will resist change, but change will still occur

Will the pH change when an acid or base is added to a buffer?

92

the pH will remain unchanged, but the buffer capacity will decrease since the concentration of weak acid and conjugate base have decreased

What will happen to the pH when water is added to dilute a buffer solution?

93

for every point difference btw the pH and pKa there is one 9 in the greater percentage of protonated versus deprotonated

Explain the rule of 9s?

94

No, their conjugates cannot act as buffers

Is there a half equivalence point for the titration of a strong acid or strong base?

95

take the average of the two pKa

How do you calculate the pI for a diprotic acid?

96

when the indicator changes color

What is the end point of a titration?

97

less products than reactants, which is why the Ka is less than 1

Will weak acid have more are less products than reactants?

98

compound contains both polar and nonpolar structures

Define amphipathic?

99

compound that contains both fat and water loving properties

Define amphiphile?

100

No, they will either 100% or 0%

Will strong acids follow the rule of 9s?

101

exothermic process since bonds are being formed

Is neutralization an exo or endothermic process?

102

a strong acid with weak base will generate a protonated salt, thus lowest pH. A strong base with weak acid will generate a salt at the highest pH

In a neutralization rxn, which two reactants will generate a salt of the lowest pH? Highest pH?