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Chem Oly Pre-Camp > Acids And Bases > Flashcards

Acids And Bases Flashcards

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
Kw expression and standard value
Kw = [H3O+] [OH-] = 1x10^-14 the equilibrium constant for the auto ionisation of water found from the equilibrium expression of auto ionisation equation
26
what is pKw formula?
pKw = pH + pOH = 14 at 25˚C pKw = -logKw
27
define autoionisation of water
water exchanging protons with itself H2O + H2O == OH- + H3O+
28
acid base conjugates
differ by one proton conj base has one FEWER H+, hence on unit more negative
29
define amphiprotic
species can ACT as an acid or a base
30
weak/strong acids in relation to H2O and H3O+
H2O < weak acid < H3O+ < strong acid strong acids are product favoured as the reactant acid > product acid (H3O+) weak acids ==
31
labeled concentration of acids vs actual concentration
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
metal (G1) oxides and water reaction
form metal hydroxide because O2- is a strong base O2- + H2O --> 2OH-
33
general rules of the strength of acid-base conjugate pairs
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
what is the acidity constant?
Ka, a property of an acid-base conjugate pair. acid + H2O == H3O+ conj base Ka = [H3O+][conj base] / [acid] or [H3O+][A-] / [HA]
35
Ka relationship with strength of acid
HIGHER Ka, STRONGER acid higher tendency to donate H+ reactant favoured = weak, Ka<1
36
pKa formula
pKa = -logKa
37
Ka formula from pKa
Ka = 10^(-pKa)
38
pKa values for weak and strong acid/conj pairs
Weak acid-base conj pairs 2 < pKa < 13 stronger acid, LOWER pKa strong acid, negative pKa
39
strong acid pKa and Ka values
high Ka, low (negative) pKa
40
strong bases pKa(conj acid) and Ka(conj acid) values
Ka(conj acid) lower, pKa(conj acid) higher
41
pKa for polyprotic acid, eg H3PO4 which to use for amphiprotic species?
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
what is an ICE table?
Initial: c(reactant) and c(products) Change: + or - change Equilibrium = Initial + Change used to calculate changes in concentration
43
Ka value for weak acid-base conj pair
Ka < 0.001 very small extent of reaction
44
assumptions for calculating [H3O+] from known Ka
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 >> [OH-] from water
45
all solutions containing weak acid/base or a mixture are at equilibrium with respect to these two equations
acid + H2O == H3O+ + conj base | H2O + H2O == OH- + H3O+
46
what is a buffer solution?
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
for a buffer, when does pH=pKa?
where [acid] = [conj base] so that Ka = [H3O+] x 1
48
for a buffer solution, when is pH
pH [base] (as [H3O+] > Ka) if [acid] < 10x [base], pH is within 1 unit of pKa
49
approximate formula of Ka
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
how is a buffer prepared?
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
formula to use when the TOTAL concentration of the buffer is given
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
identify if a proton transfer reaction is reactant or product favoured
if reactant acid and base is STRONGER than product acid, PRODUCT favoured if reactant acid weaker, reactant favoured
53
define dibasic
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
define buffer region
pH = pKa +/- 1 | the flat region on a titration graph
55
define major species
species present in relatively high concentration
56
reaction extent formula
= product concentration / initial reactant concentration x 100% where one member of the conj pair is the reactant, the other is the product
57
numerical extent of reaction for strong / weak a/b
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
define equivalence point on a graph
the point halfway up the steep rise on the graph
59
key points on a titration curve
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
titration curve axis
pH vs volume of titrant added
61
define end point
the volume at which the indicator changes colour
62
factors influencing the shape of a titration curve
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
methyl orange indicator colours
red in acid form yellow is base form pKa = 3.7 colour changes over pH=pKa+/-1
64
bromocresol purple indicator colours
Yellow in acid form Purple in base form pKa = 6.3
65
Phenolphlalein indicator colours
Colourless in acid form Purple in base form pKa = 9.6
66
define polyprotic acid
has more than one acidic Hydrogen that can be removed sequentially by OH- eg. H3PO4
67
find pH at equivalence points for amphiprotic anion
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
the extent of reaction is greater in a more ___ solution
dilute because initial concentration low ?? smallest extent of reaction w/H2O when one product already exists as a major species in equilibrium
69
at equilibrium of a weak acid, major and minor species
major: weak acid, H2O minor: conj base, H3O+, OH-
70
at equilibrium of a strong acid major and minor species
major: the conjugate base, and H3O+ (or OH- if base)
71
if both acid base members of a conj pair are in solution, major species are
both are major species | also the ion (eg. Na+, Cl-, K+)
72
acid hydrogens are always bonded to which element?
Oxygen. | more than one acidic H = polyprotic acid

Chem Oly Pre-Camp (14 decks)

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