Acids and bases

Question 1

What is a bronsted acid?

Answer 1

Proton donor

Question 2

What is a bronsted base?

Answer 2

Proton acceptor

Question 3

What is used to measure the strength of acids?

Answer 3

pKa scale

Question 4

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

Answer 4

It is large and constant (55.56 moldm-3)

Question 5

What equation dictates the strength of acid and why?

Answer 5

HA + H2O A- + H3O+

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

Question 6

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

Answer 6

Becomes lower

Question 7

What does the pKa of the acid depend on?

Answer 7

The stability of the conjugate base

Question 8

The more stable A- is…

Answer 8

The easier the deprotonation and the lower the pKa

Question 9

The stronger the base A-…

Answer 9

The weaker the conjugate acid HA

Question 10

The stronger the acid HA…

Answer 10

The weather the conjugate base A-

Question 11

What is the pKa of HI?

Answer 11

-10

Question 12

What is the pKa of HCl?

Answer 12

-7

Question 13

What is the pKa of H2SO4?

Answer 13

-3

Question 14

What is the conjugate base of H2SO4?

Answer 14

HSO4-

Question 15

What is the pKa of H3O+?

Answer 15

-2

Question 16

What is the conjugate base of H3O+?

Answer 16

H2O

Question 17

What is the pKa of HSO4-?

Answer 17

2

Question 18

What is the conjugate base of HSO4-?

Answer 18

SO4 2-

Question 19

What is the pKa of a carboxylic acid?

Answer 19

5

Question 20

What is the pKa of H2S?

Answer 20

7

Question 21

What is the pKa of NH4+?

Answer 21

9

Question 22

What is the conjugate base of NH4+?

Answer 22

NH3

Question 23

What is the pKa of a phenol?

Answer 23

10

Question 24

What is the pKa of an alcohol?

Answer 24

15

Question 25

What is the pKa of H2O?

Answer 25

15

Question 26

What is the conjugate base of H2O?

Answer 26

OH-

Question 27

What is the pKa of a ketone?

Answer 27

20

Question 28

What is the pKa of an alkyne?

Answer 28

25

Question 29

What is the pKa of NH3?

Answer 29

33

Question 30

What is the conjugate base for NH3?

Answer 30

NH2-

Question 31

What is the pKa of a benzene ring?

Answer 31

43

Question 32

What is the pKa of an alkane?

Answer 32

48

Question 33

What are the 5 factors that affect pKa and acidity?

Answer 33

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

Question 34

How does bond strength affect pKa?

Answer 34

The stronger the A-H bond, the higher the pKa | The weaker the A-H bond, the lower the pKa

Question 35

What causes a A-H bond to be strong?

Answer 35

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

Question 36

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

Answer 36

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) )

Question 37

How does delocalisationt of the negative charge affect pKa?

Answer 37

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

Question 38

How can C-H become acidic?

Answer 38

If the negative charge can be stabilised by resonance

Question 39

How do inductive effects affect pKa?

Answer 39

They stabilise A- and increase the acidity of HA

Question 40

What effect do electron donating groups do the pKa?

Answer 40

Raise it

Question 41

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

Answer 41

They stabilise the negative charge by induction electron withdrawal

Question 42

How does hybridisation affect pKa?

Answer 42

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

Question 43

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

Answer 43

It doesn't need the proton back if it stable

Question 44

What is pKaH?

Answer 44

The protonated form

Question 45

What is the pKaH of NH2-?

Answer 45

The same as the pKa of NH3 which is 33

Question 46

Why is NH3 a stronger base4 than H2O?

Answer 46

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

Question 47

The higher the pKaH of a base...

Answer 47

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

Question 48

What happens when you increase the electron density on nitrogen?

Answer 48

The base strength increases

Question 49

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

Answer 49

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

Question 50

How does hybridization affect pKaH?

Answer 50

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

Question 51

How does conjugation affect base strength?

Answer 51

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