topic 12: acid base equilibria Flashcards
bronsted lowry acid
proton donor
bronsted lowry base
proton acceptor
each acid/ base has a …
conjugate acid/base
conjugate base h2so4
hso4-
if 2 acids react, how do you know which one acts as an acid and which as a base?
greater Ka = acid
pH
- log [H+]
strong acids…
completely dissociate
weak acids
only very slightly dissociate
[H+] for a strong acid
[ acid ]
pH to what sf?
2 dp
Kw
[OH-][H+]
KW AT STANDARD CONDITIONS
1* 10 ^ -14 mol2dm-6
pH of strong base
- work out pOH
- 14 -
- or use Kw
weak acid Ka
Ka = [h+][a-] / [ha]
assumptions pH weak acid
- eqm conc H+ = eqm conc A- (1:1)
- [HA] initial = equilibrium as %age dissociation negligible
when to use half equivalence point
-weak acid has had added to it half its moles in alkali
what happens at half equivalnce point (short)
pKa = pH
prove half equivalence point
- Ka = [h+][a-]/[ha]
- assume [ha] == [a-] becuase equal volumes acid and salt
pH strong acid after 10 fold dilutions (add water)
decrease conc by 10, ph increases by 1
pH WEAK acid with tenfold dilutions (add water)
- eqm shifts to right
- conc h+ increases
- pH increases by less than 1
buffer solution
resists changes in ph when small amounts of acid or alkali are added to it
acidic buffer contains
- weak acid and its salt from a strong base
2 ways to make acidic buffer
- weak acid + strong base
- weak acid + salt
basic buffer contains
- weak base and its salt w a strong acid
how to make a basic buffer
- weak base strong acid
- weak base and its salt
how does a buffer work
- 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
pH of a buffer assumption
A- from salt only
[ha] initial = eqm
how does an indicator work
- 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
why in a weak acid strong base titration is the equiavlence point more basic?
- salt present at equivalence point
- hydrolysis of ION
- FORMING OH-
how to justify indicator choice
- equivalence point pH close to pKin
- range of pH of indicator entirely in vertical section of titration curve
blood buffer ADD CO2
h2co3 = h+ + hco3 -
- co2 dissolves in water in blood to form h2co3
- poe shifts to right
- increases conc h+
- LARGE RESERVOIR HCO3- combines
when u say u add alkali or acid , and it reacts w something in the buffer, always mention
it makes water
effect of increasing temp on rate (2)
- increases rate
- more X produced in a given time
