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Chem Oly Pre-Camp > Acids And Bases > Flashcards

Acids And Bases Flashcards

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1
Q

Common strong acids formulas

A

HNO3, H2SO4

HCl, HBr, HI

HClO4, HClO3

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2
Q

Common string bases

A

H-, N3-, O2-, OH-, alkoxide ions like CH3O-

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3
Q

define Bronsted-Lowry acid

A

proton donor

cations, anions, or molecules

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4
Q

define Bronsted-Lowry bases

A

proton acceptor

molecules or anions

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5
Q

define acid/base

A

donates/accepts protons more readily than water

upon reaction with H2O, produces more H3O+ or OH- than the reaction of water with itself.

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6
Q

Bases must have what?

A

must have an atom with a non-bonding electron pair to accept H+

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7
Q

in an acid/base reaction there is no change in…

A

oxidation number

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8
Q

define Lewis acid

A

e- pair acceptors

Acid, Acceptor

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9
Q

define Lewis base

A

e- pair donors

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10
Q

a Lewis acid-base reaction results in…

A

bond formation

making a Lewis acid-base complex

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11
Q

what is an oxoacid?

A

group of acids with an oxo group

=O

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12
Q

strengths of oxoacids depends on

A

number of oxo- groups

1 = weak acid 
CH3CO2H ethanoic acid 
H2CO3 carbonic acid
H2SO3 sulfurous acid
H3PO4 phosphoric acid 
more than 1 = strong acid 
HNO3 nitric 
H2SO4 sulfuric 
HClO4 perchloric acid 
HClO3 chloric acid
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13
Q

general rules for anions arising from weak/strong acids

A

anions arising from weak acids are weak bases

anions arising from strong acids do not change the pH of water

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14
Q

weakly basic anions (arising from weak oxoacids)

A

ethanoate ion
carbonate ion
sulfite ion
phosphate ion

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15
Q

not basic anions (arising from strong oxoacids)

A

nitrate ion
sulfate ion
perchlorate ion

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16
Q

acid strength define

A

tendency of an atom to donate a proton to a base

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17
Q

acidity of EHn trends

A

increasing –> and down

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18
Q

two factors influencing the acidity of EHn

A

POLARITY of E-H bond
more polar = more acidic (hence increase C —> F)

STRENGTH of E-H bond
longer bond = more acidic
(hence increase down, HI>HBr>HCl>HF)

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19
Q

what is the only HnX more basic than water?

A

NH3

weak base

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20
Q

how does the strength of a base relate to charge density?

A

Stronger base = HIGHER e- density, or higher e- pair availability, at the accepting atom

monatomic anions have higher charge density at X than HnX
hence the anion is more basic than HnX

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21
Q

Xn- acidity

A

all strong bases except halides

high charge density

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22
Q

reaction metal hydride and water

A

forms metal hydroxide and H2

because H- is a strong base, so ionic compounds w/ H- react completely with H2O.

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23
Q

formula for finding pH given [H3O+]

A

pH = -log[H3O+]

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24
Q

formula for finding [H2O+] given pH

A

[H3O+] = 10^(-pH)

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25
Q

Kw expression and standard value

A

Kw = [H3O+] [OH-] = 1x10^-14

the equilibrium constant for the auto ionisation of water

found from the equilibrium expression of auto ionisation equation

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26
Q

what is pKw formula?

A

pKw = pH + pOH = 14 at 25˚C

pKw = -logKw

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27
Q

define autoionisation of water

A

water exchanging protons with itself

H2O + H2O == OH- + H3O+

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28
Q

acid base conjugates

A

differ by one proton

conj base has one FEWER H+, hence on unit more negative

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29
Q

define amphiprotic

A

species can ACT as an acid or a base

30
Q

weak/strong acids in relation to H2O and H3O+

A

H2O < weak acid < H3O+ < strong acid

strong acids are product favoured as the reactant acid > product acid (H3O+)
weak acids ==

31
Q

labeled concentration of acids vs actual concentration

A

actual concentration is less due to reaction w/ H2O

STRONG = same as label, same pH

WEAK: depends on c(acid) and the strength of the weak acid, they react to different extents, hence different pH for the same c(acid)

32
Q

metal (G1) oxides and water reaction

A

form metal hydroxide
because O2- is a strong base
O2- + H2O –> 2OH-

33
Q

general rules of the strength of acid-base conjugate pairs

A

the weaker the acid, the stronger the conj base

if one member is STRONG, the other DOES NOT react with H2O to change its pH

34
Q

what is the acidity constant?

A

Ka, a property of an acid-base conjugate pair.

acid + H2O == H3O+ conj base

Ka = [H3O+][conj base] / [acid]

or [H3O+][A-] / [HA]

35
Q

Ka relationship with strength of acid

A

HIGHER Ka, STRONGER acid
higher tendency to donate H+

reactant favoured = weak, Ka<1

36
Q

pKa formula

A

pKa = -logKa

37
Q

Ka formula from pKa

A

Ka = 10^(-pKa)

38
Q

pKa values for weak and strong acid/conj pairs

A

Weak acid-base conj pairs
2 < pKa < 13

stronger acid, LOWER pKa
strong acid, negative pKa

39
Q

strong acid pKa and Ka values

A

high Ka, low (negative) pKa

40
Q

strong bases pKa(conj acid) and Ka(conj acid) values

A

Ka(conj acid) lower, pKa(conj acid) higher

41
Q

pKa for polyprotic acid, eg H3PO4

which to use for amphiprotic species?

A

one pKa for each acidic H

pK1(H3PO4) = pKa(H3PO4) 
pK2(H3PO4) = pKa(H2PO4-) 
pK3(H3PO4) = pKa(HPO4^2-)

for amphiprotic species, us pKa for the appropriate pair
eg. acid strength HPO4^2- use pK3 (HPO4^2-/PO4^3-)
base strength use pK2 (H2PO4-/HPO4^2-)

42
Q

what is an ICE table?

A

Initial: c(reactant) and c(products)
Change: + or - change
Equilibrium = Initial + Change

used to calculate changes in concentration

43
Q

Ka value for weak acid-base conj pair

A

Ka < 0.001

very small extent of reaction

44
Q

assumptions for calculating [H3O+] from known Ka

A

assume [acid] = c0(acid)
because weak acid, so insignificant amounts react
strictly, c0(acid) = [acid] + [conj base]

assume [H3O+] = [conj base]
by reaction stoichiometry

VERIFY validity of assumption:
check that [H3O-] «< c0(acid)
and [H3O+] from weak acid&raquo_space; [OH-] from water

45
Q

all solutions containing weak acid/base or a mixture are at equilibrium with respect to these two equations

A

acid + H2O == H3O+ + conj base

H2O + H2O == OH- + H3O+

46
Q

what is a buffer solution?

A

resists change in pH or dilution on addition of small amounts of strong acid/base

has active weak acid-base conj pair, both MAJOR SPECIES at that pH

47
Q

for a buffer, when does pH=pKa?

A

where [acid] = [conj base]

so that Ka = [H3O+] x 1

48
Q

for a buffer solution, when is pH

A

pH [base]
(as [H3O+] > Ka)

if [acid] < 10x [base], pH is within 1 unit of pKa

49
Q

approximate formula of Ka

A

Ka = [H3O+] x c(conj base)/c(acid)
if both acid and base are major, small extent of reaction

so Ka = [H3O+] x n(conj base)/n(acid)

50
Q

how is a buffer prepared?

A

by mixing amounts of acid and conjugate base until it has a specified pH

OR by reacting a solution containing one member of the conj pair with a strong acid/base to generate the second member

51
Q

formula to use when the TOTAL concentration of the buffer is given

A

n(acid) + n(base) = c(buffer) x V(buffer)
unknown x unknown = known x known

use with Ka expression with n to calculate two unknowns

52
Q

identify if a proton transfer reaction is reactant or product favoured

A

if reactant acid and base is STRONGER than product acid, PRODUCT favoured

if reactant acid weaker, reactant favoured

53
Q

define dibasic

A

capable of accepting either 1 or 2 protons
eg. 1,2-diaminoethane
base only

accept 1 proton, the cationic form with one tetravalent N (has +ve charge on it) is both acid and base

accept another proton, and the di-cation is a stronger acid

54
Q

define buffer region

A

pH = pKa +/- 1

the flat region on a titration graph

55
Q

define major species

A

species present in relatively high concentration

56
Q

reaction extent formula

A

= product concentration / initial reactant concentration x 100%

where one member of the conj pair is the reactant, the other is the product

57
Q

numerical extent of reaction for strong / weak a/b

A

strong = 100%

weak < 10%

if weak, extent greatest w/ strongest a/b
if there’s a common ion, the extent of reaction is LOW because it already exists in solution

58
Q

define equivalence point on a graph

A

the point halfway up the steep rise on the graph

59
Q

key points on a titration curve

A

halfway along the flat buffer region: the point where [a]=[b] and pKa = pH
to either side, [a]>[b] or vice versa

equivalence point - halfway up steep rise

60
Q

titration curve axis

A

pH vs volume of titrant added

61
Q

define end point

A

the volume at which the indicator changes colour

62
Q

factors influencing the shape of a titration curve

A

initial pH = substance in the flask
final pH = equal to that of diluted titrant
direction - which is added to which

strong = larger steep change section, change in pH of 8-10 units 
weak = smaller steep section, change in pH of 4-6 units
63
Q

methyl orange indicator colours

A

red in acid form
yellow is base form
pKa = 3.7
colour changes over pH=pKa+/-1

64
Q

bromocresol purple indicator colours

A

Yellow in acid form
Purple in base form
pKa = 6.3

65
Q

Phenolphlalein indicator colours

A

Colourless in acid form
Purple in base form
pKa = 9.6

66
Q

define polyprotic acid

A

has more than one acidic Hydrogen that can be removed sequentially by OH-
eg. H3PO4

67
Q

find pH at equivalence points for amphiprotic anion

A

pH independent of concentration of the solute, given by

pH = 1/2 (pK1+pK2)
graphically, equivalence point halfway between the two flat buffer regions of pK1 and pK2

68
Q

the extent of reaction is greater in a more ___ solution

A

dilute
because initial concentration low ??

smallest extent of reaction w/H2O when one product already exists as a major species in equilibrium

69
Q

at equilibrium of a weak acid, major and minor species

A

major: weak acid, H2O
minor: conj base, H3O+, OH-

70
Q

at equilibrium of a strong acid major and minor species

A

major: the conjugate base, and H3O+ (or OH- if base)

71
Q

if both acid base members of a conj pair are in solution, major species are

A

both are major species

also the ion (eg. Na+, Cl-, K+)

72
Q

acid hydrogens are always bonded to which element?

A

Oxygen.

more than one acidic H = polyprotic acid

Chem Oly Pre-Camp (14 decks)

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