topic 12: acid base equilibria

Question 1

bronsted lowry acid

Answer 1

proton donor

Question 2

bronsted lowry base

Answer 2

proton acceptor

Question 3

each acid/ base has a …

Answer 3

conjugate acid/base

Question 4

conjugate base h2so4

Answer 4

hso4-

Question 5

if 2 acids react, how do you know which one acts as an acid and which as a base?

Answer 5

greater Ka = acid

Question 6

pH

Answer 6

• log [H+]

Question 7

strong acids…

Answer 7

completely dissociate

Question 8

weak acids

Answer 8

only very slightly dissociate

Question 9

[H+] for a strong acid

Answer 9

[ acid ]

Question 10

pH to what sf?

Answer 10

2 dp

Question 11

Kw

Answer 11

[OH-][H+]

Question 12

KW AT STANDARD CONDITIONS

Answer 12

1* 10 ^ -14 mol2dm-6

Question 13

pH of strong base

Answer 13

• work out pOH
• • 14 -
• or use Kw

Question 14

weak acid Ka

Answer 14

Ka = [h+][a-] / [ha]

Question 15

assumptions pH weak acid

Answer 15

• eqm conc H+ = eqm conc A- (1:1)
• [HA] initial = equilibrium as %age dissociation negligible

Question 16

when to use half equivalence point

Answer 16

-weak acid has had added to it half its moles in alkali

Question 17

what happens at half equivalnce point (short)

Answer 17

pKa = pH

Question 18

prove half equivalence point

Answer 18

• Ka = [h+][a-]/[ha]
• assume [ha] == [a-] becuase equal volumes acid and salt

Question 19

pH strong acid after 10 fold dilutions (add water)

Answer 19

decrease conc by 10, ph increases by 1

Question 20

pH WEAK acid with tenfold dilutions (add water)

Answer 20

• eqm shifts to right
• conc h+ increases
• pH increases by less than 1

Question 21

buffer solution

Answer 21

resists changes in ph when small amounts of acid or alkali are added to it

Question 22

acidic buffer contains

Answer 22

• weak acid and its salt from a strong base

Question 23

2 ways to make acidic buffer

Answer 23

• weak acid + strong base
• weak acid + salt

Question 24

basic buffer contains

Answer 24

• weak base and its salt w a strong acid

Question 25

how to make a basic buffer

Answer 25

- weak base strong acid - weak base and its salt

Question 26

how does a buffer work

Answer 26

- large reservoir of acid + salt or base + salt - write equation for dissociation - h+ added reacts with ... - shifts poe to ... - oh- added reacts with ... - shifts poe to... - ratio (ref ka expression) unchanged therefore resists change in pH

Question 27

pH of a buffer assumption

Answer 27

A- from salt only [ha] initial = eqm

Question 28

how does an indicator work

Answer 28

- weak acid - ha = h+ + a- - ADD ACID: shifts poe to left, colour of HA seen - ADD ALKALI: reacts w H+, shifts poe to right, colour of a- seen

Question 29

why in a weak acid strong base titration is the equiavlence point more basic?

Answer 29

- salt present at equivalence point - hydrolysis of ION - FORMING OH-

Question 30

how to justify indicator choice

Answer 30

- equivalence point pH close to pKin - range of pH of indicator entirely in vertical section of titration curve

Question 31

blood buffer ADD CO2

Answer 31

h2co3 = h+ + hco3 - - co2 dissolves in water in blood to form h2co3 - poe shifts to right - increases conc h+ - LARGE RESERVOIR HCO3- combines

Question 32

when u say u add alkali or acid , and it reacts w something in the buffer, always mention

Answer 32

it makes water

Question 33

effect of increasing temp on rate (2)

Answer 33

- increases rate - more X produced in a given time

Question 34

why is the conc of h+ in eg a diprotic acid not 2x the initial

Answer 34

- first Ka is very large so acid fully dissociates - so , lots of h+ from first diss means poe lies further to the left, so Ka of second dissocaition is much smaller, so much less h+ produced from second dissociation