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Physical Chemistry > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

What do all acids release

A

H+

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2
Q

What do all bases accept

A

H+

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3
Q

Common bases

A

Metal oxides
Metal hydroxides
Ammonia and amines

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4
Q

Alkalis (soluble bases that dissolve in water release in water

A

OH- ions

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5
Q

How are salts made

A

When H+ from acid is replaced by a metal ion/another positive ion

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6
Q

Neutralisation reactions

A 
Acids react with:
carbonates to form CO2
bases (metal oxides) to form H2O
alkalis to form H2O
Metals to form H
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7
Q

Redox reactions

A

Acids react with metals
Metal is oxidised
Hydrogen is reduced

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8
Q

Ammonia

A

Forms weak alkaline solution when dissolved in H2O

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9
Q

Salt crystals features

A

Have water = crystalline form, hydrated
No water = powdered form, anhydrous
Molar proportion of H2O 名前 water of crystallisation

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10
Q

Hydrated salt formula

A

1: calculate n of anhydrous
2: calculate n of H2O
3: determine hydrated salt ormula

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11
Q

Titration calculation method

A

1) find n of compound in the sol
2) use equation to ID mol no. of substances in 2nd sol.
3) ID n for any other relevant substances
4) scale quantities to match
5) calculate M

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12
Q

Bronsted-Lowry model

A

(conjugate) Acid = H+ donor
(conjugate) Base = H+ acceptor
Alkali = base that dissolves in H2O forming OH-

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13
Q

Water’s acid-base equilibrium

A

Ha(aq) ⇌ H+(aq) + A-(aq)

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14
Q

Acid strength

A

Extent to which it dissociates into H+ and A-

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15
Q

Strong acid strength

A

Almost complete dissociation

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16
Q

Weak acid strength

A

Partial dissociation

Equilibrium favours non-dissociated side

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17
Q

Ka, acid dissociation constant

A

Dissociated side/non-dissociated side

Unit = mol dm-3

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18
Q

Large vs small Ka

A

Large Ka = large dissociation, strong acid

Small Ka = small dissociation, weak acid

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19
Q

Concentration vs strength of acid

A

Concentration = amount of acid dissolved in 1dm3 o solution

Strength=dissociation extent

20
Q

pH formula

A

pH=-log10 [H+(aq)]

21
Q

H+ formula

A

[H+(aq)]= 10-pH

22
Q

pH value meanings

A

Low H+ value = high pH value

High H+ value = low pH value

23
Q

pH changed by 1 =

A

H+ changed by 10x

24
Q

Strong acid pH calculations

A

Found directly from acid concentration

[H+]=[HA]

25
Q

Weak acids pH calculation

A

Need acid concentration and Ka value
Consider:
[HA(aq)]equilibrium ≈ [HA(aq)]start
[H+(aq)] ≈ [A-(aq)]

Formula therefore:
Ka ≈ [H+(aq)]2/[HA(aq)]

26
Q

pKa and Ka link

A

Logarithmic version of Ka

pKa = -log10Ka
Ka = 10-pKa

Low Ka = high pKa
High Ka = low pKa

27
Q

Kw

A

Ionic product of water

Kw=[H+(aq)][OH-(aq)]

28
Q

Kw at 25 degrees

A

Kw=1.0x10-14 mol2 dm-6

29
Q

H+ and OH- in water

A

Same concentrations,
10-7 mol dm-3. Total therefore:
10-14 mol dm-3

30
Q

H+ vs OH- concentrations

A

Water: H+ = OH-
Acid: H+ > OH-
Alkaline: H+ < OH-

Linked by Kw

31
Q

Strong alkalis pH calculation

A

1) Find concentration directly from alkali concentration
2) solve for H+ ( Kw/OH-)
3) calculate pH

32
Q

Titration curve features

A

Mid-point of vertical bit is Equivalence Point

Indicator is only suitable if its pKind value is within the pH range of the vertical part

33
Q

Ka from a titration curve

A

1) Get vol. of alkali for neutralisation from titearion curve
2) get pH at half-neutralisation fron curve
3) half-neut, HA = A-, so Ka = H+
Ka = 10-pH

34
Q

∆Hneut value

A

Approximately -57.9kJ mol -1 for strong acids

Less exothermic for weak acids

35
Q

Buffer soluions

A

Minimise pH changes by removing most of added acid/alkali

Made of HA and its conjugate base

36
Q

Adding H+ to a buffer

A

H+ is increased
pH change is opposed. Equilib moves left removing H+ and forming HA
A- removes most of added H+

37
Q

Adding alkali to buffer

A

Added OH- reacts with small concentration of H+
pH change opposed by moving equil to the right, restoring H+ as HA dissociates
HA restores most of lost H+

38
Q

Buffer solution pH depends on

A
  • Ka of buffer system

* ratio of weak acid and its conjugate base

39
Q

Arrhenius acids and bases

A

Acids: dissociate in water to make H3O+
Bases: dissociate to make OH-

40
Q

Lewis acids and bases

A

Acid aka electrophile: e- acceptor

Base aka nucleophile: e- donator

41
Q

Acid-conjugate base link

A

Acids are directly proportional to conjugate base’s stability.
More stable = more acidic

42
Q

Base stability considerations

A 
Larger atoms いい
More electronegative いい
sp hybridised >sp2>sp3 いい
e- withdrawing groups on acid いい
Resonance structures いい
43
Q

pKa values

A

V strong acids = pKa &<0

Weak acids = pKa 0-9

44
Q

Equilibrium rule

A

Equilibrium of a reaction will favour side with weaker acids and bases

45
Q

Acid dissociation constant

A

Ka = [H+][A-]/[HA]

46
Q

Buffer solution pH

A

pKa + log10 (salt/acid)

Physical Chemistry (11 decks)

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