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CHY1101 - Organic chemistry > Acids and bases > Flashcards

Acids and bases Flashcards

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1
Q

What is a bronsted acid?

A

Proton donor

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2
Q

What is a bronsted base?

A

Proton acceptor

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3
Q

What is used to measure the strength of acids?

A

pKa scale

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4
Q

Why is the value of water ignored in the equilibrum constant equation?

A

It is large and constant (55.56 moldm-3)

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5
Q

What equation dictates the strength of acid and why?

A

HA + H2O A- + H3O+

Energy of products and reactants are looked at and compared to determine if the reaction is favourable

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6
Q

What happens to pKa when the HA becomes a stronger acid?

A

Becomes lower

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7
Q

What does the pKa of the acid depend on?

A

The stability of the conjugate base

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8
Q

The more stable A- is…

A

The easier the deprotonation and the lower the pKa

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9
Q

The stronger the base A-…

A

The weaker the conjugate acid HA

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10
Q

The stronger the acid HA…

A

The weather the conjugate base A-

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11
Q

What is the pKa of HI?

A

-10

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12
Q

What is the pKa of HCl?

A

-7

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13
Q

What is the pKa of H2SO4?

A

-3

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14
Q

What is the conjugate base of H2SO4?

A

HSO4-

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15
Q

What is the pKa of H3O+?

A

-2

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16
Q

What is the conjugate base of H3O+?

A

H2O

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17
Q

What is the pKa of HSO4-?

A

2

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18
Q

What is the conjugate base of HSO4-?

A

SO4 2-

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19
Q

What is the pKa of a carboxylic acid?

A

5

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20
Q

What is the pKa of H2S?

A

7

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21
Q

What is the pKa of NH4+?

A

9

22
Q

What is the conjugate base of NH4+?

A

NH3

23
Q

What is the pKa of a phenol?

A

10

24
Q

What is the pKa of an alcohol?

A

15

25
Q

What is the pKa of H2O?

A

15

26
Q

What is the conjugate base of H2O?

A

OH-

27
Q

What is the pKa of a ketone?

A

20

28
Q

What is the pKa of an alkyne?

A

25

29
Q

What is the pKa of NH3?

A

33

30
Q

What is the conjugate base for NH3?

A

NH2-

31
Q

What is the pKa of a benzene ring?

A

43

32
Q

What is the pKa of an alkane?

A

48

33
Q

What are the 5 factors that affect pKa and acidity?

A 
Weak A-H bonds 
Stability of the conjugate base 
Delocalisation of the negative charge 
Inductive effects
Hybridisation
34
Q

How does bond strength affect pKa?

A

The stronger the A-H bond, the higher the pKa

The weaker the A-H bond, the lower the pKa

35
Q

What causes a A-H bond to be strong?

A

If there is a good overlap of the s orbital from hydrogen and the p orbital of the molecule attached

36
Q

How does stability of the conjugate base (A-) affect pKa?

A

The negative charge being on the electronegative atom in the conjugate base
The more electronegative the atom, the more acidic and the lower the pKa (eg. F- is more acidic (pKa = 3) than -CH3 (pKa = 48) )

37
Q

How does delocalisationt of the negative charge affect pKa?

A

It makes A- more stable and HA more acidic, lowering the pKa

38
Q

How can C-H become acidic?

A

If the negative charge can be stabilised by resonance

39
Q

How do inductive effects affect pKa?

A

They stabilise A- and increase the acidity of HA

40
Q

What effect do electron donating groups do the pKa?

A

Raise it

41
Q

What do flurorines do to a molecule with a negative charge?

A

They stabilise the negative charge by induction electron withdrawal

42
Q

How does hybridisation affect pKa?

A

Looking at Sp3, sp2 and sp orbitals, the more ‘s’ character, the lower the energy and the lower the pKa. More acidic

43
Q

Why is the more stable A- the weaker it will be as a base?

A

It doesn’t need the proton back if it stable

44
Q

What is pKaH?

A

The protonated form

45
Q

What is the pKaH of NH2-?

A

The same as the pKa of NH3 which is 33

46
Q

Why is NH3 a stronger base4 than H2O?

A

The lone pair on nitrogen is much easier to donate than the lone pair on oxygen and N is less electronegative

47
Q

The higher the pKaH of a base…

A

The weaker the acid it comes from and the stronger the base A- will be

48
Q

What happens when you increase the electron density on nitrogen?

A

The base strength increases

49
Q

Why are tertiary amines less basic than primary or secondary amines in solution?

A

The positive charge cannot be stabilised by solvation as once protonated there is only one chance for hydrogen bonding compared to three on primary amines

50
Q

How does hybridization affect pKaH?

A

The more s character in an orbital, the lower the pKaH and the weaker it is as a base

51
Q

How does conjugation affect base strength?

A

The more conjugation, the more stable the electron pair so the base strength decreases

CHY1101 - Organic chemistry (22 decks)

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