Acids and Bases

Question 1

what is the equation for the self- ionistaion of water ?

Answer 1

H20 + H20 ——–> H30+ + OH-

Question 2

why is water known as an amphoteric ?

Answer 2

• water acts as a base and as an acid

Question 3

what is the equation for Kw?

Answer 3

• Kw = [H30+] [OH-]

Question 4

what is the value of Kw at 25c

Answer 4

• 1 x 10-14

Question 5

why does Kw increase with temperature ?

Answer 5

• ionisation of water is an endothermic process

Question 6

what is the relationship between PH,Ka and Pka

Answer 6

• high ka = stronger acid = smaller Ph
• larger ka = smaller pka

Question 7

how do u calculate pOH ?

Answer 7

• log[OH-]

Question 8

what equation links pH and pOH ?

Answer 8

• pH +pOH = 14

Question 9

what is the equation for Ka ?

Answer 9

Ka = [H3O+][A-] / [HA]
OR
Ka = [H3O+]^2 / [HA]

Question 10

what is equation for Kb ?

Answer 10

Kb = [HB+][OH-] / [B]

Question 11

what does a more electronegative atom on the acid mean ?

Answer 11

-conjugate base is more stable

Question 12

how does anion size affect acidity ?

Answer 12

• increasing size = increased acidity
• as size increases, bond between H and ion is easier to break
• so H+ is more easily donated

Question 13

how does strength of the acid affect strength of conjugate base ?

Answer 13

• stronger acid = weak conjugate base / stable

Question 14

what is delocalization ?

Answer 14

• charge is spread out across a molecule because e- are free to move

Question 15

how does delocalization stabilize a molecule ?

Answer 15

• delocalization allows for resonance structures and stabilization

Question 16

which is more stable a weaker or stronger conjugate base ?

Answer 16

• weaker conjugate base

Question 17

why is acetate ion more stable than ethoxide ion ?

Answer 17

• e - are localised in ethoxide
• no resonance structures
• so less stable

Question 18

How does the inductive effect increase acidity ?

Answer 18

• halogens are more electronegative
• pulls e- towards itself
• pulls e- through sigma bonds
• this decreases electron density
• base is more stable/ weak
• acid is stronger

Question 19

How does hybridization affect acid strength ?

Answer 19

• atoms with higher percent of s character are more acidic
• lone pair is held closer to nucleus
• more stable / weaker conjugate base

Question 20

what is the s character of a hybrid orbital ?

Answer 20

• percentage of s in it
• sp = 50
• sp2 = 33
• sp3 = 25

Question 21

what is a Bronsted-Lowry acid ?

Answer 21

• proton donor

Question 22

what is a Bronsted-Lowry base ?

Answer 22

• proton acceptor

Question 23

what is a Lewis acid ?

Answer 23

• electron pair acceptor

Question 24

what is a Lewis base ?

Answer 24

• electron pair donor

Question 25

what factors determine the stability of a conjugate base ?

Answer 25

- electronegativity - size of anion - resonance - hybridization - inductive effects HEIRS

Question 26

how does electrongeativity affect strength of an acid ?

Answer 26

- created a polar bond, H becomes more positive so it is easier to break the bond

Question 27

Are all Bronsted Lowry acids Lewis acids?

Answer 27

Yes, but not all Lewis acids, are Bronsted Lowry acids

Question 28

How do you know if salt is more acidic or basic ?

Answer 28

- need ka and kb values whichever is greater dominates

Question 29

What is the common ion effect ?

Answer 29

- shift in equilibrium caused by addition of a compound that has an ion in common with the dissolved substance

Question 30

what effect does a common ion have on ionisation of a weak acid/base ?

Answer 30

- suppresses ionisation - because equilibrium shifts to favour reactants so less H+ /OH- conc

Question 31

What is the effect of having a weak acid and its salt in solution ?

Answer 31

- creates a buffer solution - ionisation of HA suppressed by presence of A- - hydrolysis of A- suppressed due to HA

Question 32

what happens if a strong base is added to a buffer?

Answer 32

- HA+ OH- ---> A-+H20 - pH only changes slightly

Question 33

what happens if a strong acid (HCL) was added to a buffer ?

Answer 33

* HCl---> H+ +Cl- * H+ + A- --> HA * slight change in pH

Question 34

What is a buffer ?

Answer 34

- minimises change in pH upon addition of a small amount of acid or base - made of weak acid + conjugate base

Question 35

what is the halfway point of weak acid / strong base titrations ?

Answer 35

- [HA] = [A-] so pka = pH

Question 36

what is the Henderson-Hasselbalch equation and what is it used for ?

Answer 36

- used to find the pH of a buffer - pH = pKa + log [A-]/[HA]

Question 37

what happens to blood pH when you hypo-ventilate ?

Answer 37

- acidosis - pH drops

Question 38

what happens to blood pH when you hyperventilate

Answer 38

- alkalosis - rise in pH

Question 39

What happens when blood pH drops ?

Answer 39

- increased conc of H2CO3 by protonation of HCO3- - H2Co3 looses water to form CO2aq which is coverted to co2 gas

Question 40

What happens when blood ph rises ?

Answer 40

- inc conc of hco3- by deprotination of H2CO3, breathing rate changes

Question 41

Anti-log of Henderson equation

Answer 41

[acid] / [base]= 10^(pKa-pH)

Question 42

What is the Henderson Hasselbalch equation ?

Answer 42

pH = pKa + log [A-] / [HA-]

Question 43

What is equation % acid = 100 /1 + 10^(pH - pKa)

Answer 43

- if group is acidic gives % of unionised - if basic group gives % ionised