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CHEM111 > Acids And Bases > Flashcards

Acids And Bases Flashcards

1
Q

What is a Bronsted acid / base?

A

Bronsted acid is a proton donor

Bronsted base is a proton acceptor

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2
Q

How do you measure the strength of Bronsted acids?

A

Through acidity constant Ka

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3
Q

How do you find the Ka?

A
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4
Q

How do you find pKa?

A

-log [ Ka ]

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5
Q

How does a high/low pKa value relate to acidity?

A

Strong acid = pKa < 0

Weak acid = pKa > 0

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6
Q

What is the autoionisation of water?

A

Where water splits into into conjugate acid and base pairs, this happens rapidly and at very low concentrations

Hence the value for Kw being so small

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7
Q

What is the value for Kw?

A

Kw = 1.00 x 10 x 10^14

(At 25˚C)

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8
Q

How do you calculate Kb?

A
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9
Q

What’s the relationship between a Bronsted acid and its conjugate base?

A

The stronger a Bronsted acid, the weaker is its conjugate base - and vice versa

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10
Q

Give an example of a polyprotic acid, and explain what one is

A

H3PO4 - an species with more than 1 acidic H

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11
Q

Why does order of acid strength decrease in polyprotic acids as more protons dissociate?

A

Harder to remove a proton from a negatively charged species than a neutral species

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12
Q

What are oxo-acids?

A

They are acid that contain oxygen, more specifically the acidic H is bound by a hydroxyl group

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13
Q

How does the strength increase with oxo-acids?

A

Strength of oxoacids increases with the number of unprotonated Oxygen atoms

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14
Q

What are Paulings rules for oxoacids?

A

1 for the oxoacid OpE(OH)q the pKa ≈ 8-5p

2 successive pKa values for polyprotic acids (q>1) will increase by ≈ 5 pKa units for each successive proton transfer

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15
Q

What are the 3 classes of Bronsted acids?

A

Aqua acids - coordinated with H2O molecules

Hydroxo-acids - OH with no neighbouring =O

Oxo-acids - OH with neighbouring =O

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16
Q

Why are buffer solutions important?

A

They resist change in pH

  • essential in maintaining pH in living organisms
  • used in lab to maintain correct pH
  • used in food industry as acidity regulators
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17
Q

What are buffer solutions?

A

A solution of a weak acid or base and its conjugate salt

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18
Q

What equation is used when working with buffers?

A

The Henderson-Hasselbach equation

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19
Q

What the relationship between pKa and pKw? How’s this important?

A

pKa = pKw - pKb

Helps when using HH equation as you need pKa not pKb

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20
Q

What are Lewis acids and bases?

A

Lewis acid is a lone pair donor

Lewis acid is a lone pair acceptor

21
Q

What are Lewis acids and bases in organic chemistry?

A

Lewis acid = electrophile

Lewis base = nucleophile

22
Q

What is any Bronsted acid HA of Lewis acid H+ and Lewis base A-?

A

An adduct of the Lewis acid and base

23
Q

Give an example of a Group 14 Lewis acid

A

SiF4 - electron precise compound

Si can become hypervalent and forms an octahedral [SiF6]2-

24
Q

What must a Lewis acid have or be able to do?

A

A Lewis acid must have less than an octet of valence e-

Or be able to become hypervalent

25
Q

Give an example of a Group 13 Lewis acid

A

BF3

Boron is electron deficient - requires 2 e- to complete its octet and so acts as a Lewis acid

26
Q

What are the uses of BX3s?

A

BX3s are used as Lewis acid catalysts in synthetic chemistry

27
Q

What relation does SbF5 have to ‘superacids’?

A

BF5 is already hypervalent but can still act as a powerful Lewis acid

SbF5 can accept a F from 2HF, creating SbF6- and H2F+ —> SUPERACID

28
Q

What’s SbF5 relation to ‘magic acid’?

A
29
Q

Why are AsX5 and SbX5 strong Lewis acids?

A

Because both Sb and As can become hypervalent, AND Cl and F are both very electronegative

30
Q

Give an example of a powerful Group 16 Lewis acid

A

SO3 - electron deficient, needs 2e-

Powerful Lewis acid which forms an adduct with bases such as amines

Reaction with H2O forms H2SO4

31
Q

Give an example of a group 15 Lewis acid

A

SbF5

AsX5

32
Q

Give an example of a powerful Group 16 Lewis acid

A

SO3 - electron deficient, needs 2e-

Forms addicts with bases such as amines

Rwacvtion with H2O forms sulfuric acid

33
Q

Why are solvents as acids/bases important?

A

Because most chemical reactions take place in solution

Acid/base properties can influence outcome of a reaction

34
Q

Give an example of a polar aprotic solvent

A

Acetonitrile

DMSO

DMF

35
Q

What is needed for Lewis base solvents?

A

For the solvent to have lone pairs

Can form adducts with Lewis acidic solutes

36
Q

How do steric effects impact acid/base chemistry?

A

Steric effects can influence Lewis acid/base interactions

37
Q

How do steric effects impact HMDS?

A

Weak Lewis base due to steric hindrance - weak e- pair donor

Powerful Bronsted base - very strong proton acceptor

38
Q

What period of elements are Lewis acids if they have fewer then 8 e-?

A

2nd row

39
Q

What do hard bases from stable adducts with?

A

With hard acids

40
Q

What do soft acids form stable adducts with?

A

With soft bases

41
Q

What’s the difference between hard and soft acids?

A

Hard acids/bases form predominantly ionic bonds/species

Soft acids/bases

42
Q

An atom/ion is polarisable if…

A

It’s electron distrustion can be easily distorted

43
Q

Give the characteristic of HARD acids/bases

A

Hard Lewis acids:
- cations have noble gas e- configurations
- small highly charged cations
- high oxidation states

Hard Lewis bases:
- very electronegative donor atoms

44
Q

Give the characteristics of SOFT Lewis acids/bases

A

Soft Lewis acids:
- don’t have noble gas configurations
- heavy metals
- low oxidation states

Soft Lewis base:
- larger donor atoms
- less electronegative donor atoms

45
Q

What are Lithophiles?

A

Occur as oxides/other ionic compounds, e.g. Ca, Na, Al, Ti

Cations are hard Lewis acids
- rock-loving
- remain on or near earths surface that readily form oxides that don’t sink to core

46
Q

What are Chalcophiles?

A

Occur as sulphides, e.g. Cu, Ag, Hg, Pb

Cations are soft Lewis acids
- sulfur/chalogen loving
- remain close to earths surface readily forming sulfides that are denser than ore of lithophiles so sink but not to the core

47
Q

Why is the HSAB concept useful?

A

Can be used to predict the direction of a reaction

48
Q

When log K is bigger what doe this mean?

A

Stronger bond, hence more stable adduct bound

CHEM111 (12 decks)

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