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CHM135 > Acids and Bases > Flashcards

Acids and Bases Flashcards

1
Q

Arrhenius acid

A

a substance that dissociates in water to produce hydrogen ions, H+

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2
Q

Arrhenius base

A

a substance that dissociates in water to produce hydroxide ions, OH-

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3
Q

shortfalls of Arrhenius theory

A

works with many compounds in water, but misses some (particularly bases), and clearly doesn’t describe non-aqueous solutions

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4
Q

bronsted Lowry acid

A

a substance that can give a hydrogen ion (proton donor)

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5
Q

bronsted Lowry base

A

a substance that can take a hydrogen ion (proton acceptor)

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6
Q

difference/similarity between BL bases and Arrhenius bases

A

D: B-L bases do not need to contain OH-
S: they can generate OH- when in water

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7
Q

general equation for a Bronsted Lowry acid and base interacting

A

HA + B <—> BH+ + A-

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8
Q

conjugate acid-base pairs

A

chemical species whose formulas differ by only one H+

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9
Q

acid dissociation

A

HA + H2O <–> H3O+ + A-
- an equilibrium
- H2O solvent is an (almost) pure liquid so is not in equilibrium expression
- Ka only describes the reaction of an acid with the solvent H2O as the base
- the stronger the acid, the larger the Ka

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10
Q

base dissociation

A

B + H2O <–> OH- + BH+
- stronger the base, the larger the Kb

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11
Q

amphiprotic

A

can both donate and accept protons

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12
Q

amphoteric

A

can act as both an acid and a base

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13
Q

dissociation of water

A

H2O + H2O <–> H3O+ + OH-
Kw = [H3O+][OH-] = 1 x 10^-14

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14
Q

pH =

A

-log[H3O+]

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15
Q

[H3O+] =

A

10^-pH

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16
Q

pOH =

A

-log[OH-]

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17
Q

[OH-] =

A

10^-pOH

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18
Q

basic solution
neutral solution
acidic solution

A
  • [H3O+]<[OH-], pH > 7
  • [H3O+] = [OH-], pH = 7
  • [H3O+]>[OH-], pH < 7
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19
Q

strong acid

A

fully dissociates in water
Ka&raquo_space; 1

20
Q

weak acid

A

partially dissociates in water
Ka = 1

21
Q

inert acid

A

does not dissociate in water

22
Q

conjugates:

A

strong acid <-> ‘inert’ base
weak acid <-> weak base
‘inert’ acid <-> strong base

23
Q

compare strong acids/bases and weak acids/bases as electrolytes

A

strong acids and strong bases are strong electrolytes. we assume they ionise completely in water.

weak acids and weak bases are weak electrolytes. they ionise to a limited but detectable extent in water

24
Q

The levelling effect

A

for a strong acid in water, the ‘active proton donor’ isn’t HA, its H3O+
for a strong base in water, the active proton acceptor is OH-
- different strong acids usually have different Ka’s
- however, in water, they exhibit the similar acidic properties, i.e. the acid strength of H3O+

25
Q

pKa + pKb =

A

14

26
Q

distinguish between pH, pKa and Ka

A

pH measures the acidity of the solution and depends on the absolute [H3O+]

pKa and Ka reflect the strength of the acid molecule and depends on the relative concentration at equilibrium

27
Q

percent dissociation

A

a common and useful description of a weak acid in solution

% dissociation = [HA]dissociated/[HA]initial x 100

28
Q

factors that affect acid strength

A
  1. degree of polarity of H-A bond
  2. strength of H-A bond
  3. oxoacids
29
Q

degree of polarity of H-A bond

A

depends upon the electronegativity of A
the more polar the H-A bond, the stronger the aid

30
Q

strength of H-A bond

A

depends on the size of the A atom. the larger the A atom, the longer/weaker the bond, the stronger the acid

31
Q

along the period, the most important factor is

A

electronegativity

32
Q

down the group, the most important factor is

A

the H-A bond strength

33
Q

oxoacids

A

YOm(HO)n
- eg H3PO4
- if same structure, different Y: acid strength increases as the electronegativity of Y increases
- a more electronegative Y pulls electron density away from O-H bonds, making it easier for H+ to dissociate
- the strength of oxoacids also increases with m, the number of lone oxygen atoms
- the electronegative oxygen atoms pull electron density from the chlorine, making it more positive, which in turn weakens the O-H bond

34
Q

salt solutions from conjugates of strong acids and strong bases are

A

neutral

35
Q

strong acids

A

HClO4, H2SO4, HNO3, HCl, HBr, HI

36
Q

strong bases

A

LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

37
Q

salts that are derived from a weak base and strong acid yield

A

acidic solutions

38
Q

why does weak base + strong acid give acidic solutions?

A

forms weak conjugate acid of a weak base which then dissociates
eg NH4Cl (see slides)
- solutions of NH4Cl are acidic because the ammonium ion (NH4+, a weak acid) will dissociate while the chloride ion does not

39
Q

salts, such as NaCN, that are derived from a strong base (eg NaOH) and a weak acid (eg HCN) yield basic solutions

A

see slides for example

40
Q

Ka>Kb
Ka<Kb

A

solution contains excess H3O+ ions so pH < 7
solution will contain excess OH- ions so pH>7

41
Q

Lewis acid

A

a species that accepts an electron pair

42
Q

Lewis base

A

a species that donates an electron pair

43
Q

hydrated metal cations

A

small, highly-charged metal ions (eg Al3+) form complexes in water
the resulting complexes are proton donors

44
Q

acid rain

A
  • pollutants such as sulfur oxides and nitrogen oxides dissolve in rain to form acids
  • buildings and monuments made of marble and limestone eroded by acid rain
45
Q

state the 2 equations for acid rain

A
46
Q

ions that do not react appreciably with water to produce either H3O+ or OH-

A

conjugate cations from strong bases:
- alkali metal cations (group 1)
- alkaline earth metal cations (group 2)

conjugate anions from strong monoprotic acids
- Cl-, Br-, I-, NO3-, ClO4-

because they are inert

CHM135 (23 decks)

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