5.1.3 Acids, Bases and Buffers Flashcards
what is an acid
proton donors
what is a base
proton acceptors
what is a conjugate base
the base formed after the acid loses its proton
what is a conjugate acid
the acid formed after a proton is gained
what is a strong acid
when the H+ ions completely dissociate
what is a weak acid
when the H+ ions slightly dissociate
what is amphoteric
when a substance can act as both an acid and a base
why is water an ampholyte
it can accept or donate a proton
give examples of a strong acid
HCl, H2SO4, HNO3
give examples of a weak acid
CH3COOH, H2CO3
give examples of a strong base
NaOH, KOH
give examples of a weak base
NH3
describe equilibrium in strong acids and bases
equilibrium lies to the right as most of the acid molecules have dissociated the solution is a strong electrical conductor
describe equilibrium in weak acids and bases
equilibrium lies to the left hand side as most of the acid molecules do not dissociate and the solution is a weak electrical conductor
pH=
-log[H+]
[H+]=
10^-pH
what is a strong monobasic acid
only one proton is donated per acid molecule e.g HCl
what is a strong dibasic acid
two protons are donated per acid molecule e.g H2SO4
what equation is associated with neutral
[H+]=[OH-]
what equation is used with water and what is the Kw constant
Kw=[H+][OH-] so Kw=[H+]^2 because [H+]=[OH-] Kw=1x10^-14 at 298k and 1atm
give the calculation for weak acid
[H+]=square root of Kax[HA]
ka=H+^2/HA
H+=A-
give the calculation for bases
[H+]=Kw/[OH-]
give the calculation for water
Kw=[H+]^2
give the calculation for buffers with a salt
[H+]=Ka x (HA/A-)
give the calculation for buffers with a strong base
nHA new = nHA initial - nOH-
[H+]=Ka x (HA/A-)
describe the dissociation of water
-endothermic so increasing temperature shifts equilibrium to the right increasing H+ so pH decreases
give the basic reaction for a weak acid
HA H+ + A-
give the basic reaction for ionic product of water
H2O H+ + OH-
give the calculation of working out pH of a diluted
[H+]=old volume/new volume x old [H+]
pH=-log[H+]
how do you construct a pH curve
- measure initial pH of the acid
- add alkali in small amounts
- record pH
- when approaching end point add smaller amount
describe equilibrium in indicators and give the equation
- HA H+ + A-
- in acid there is a lot of H+ so equilibrium favours the left hand side
- in alkali the H+ is used up so equilibrium shifts to the right
what is the endpoint in indicators
when there are equal amounts of both colours HA=A-
what is the equivalence point in indicators
- when the number of moles of acid exactly match the number of moles of alkali
- [H+]=[OH-]
what is a buffer
solutions that resist changes in pH upon addition of small amounts of acid or alkali
what does a buffer contain
- a solution of a weak acid and high concentration of its conjugate base and excess HA
- HA=A- + H+
describe what happens to equilibrium when a acid is added to a buffer
- acid provides more H+ that react with A-
- equilibrium shifts to the left hand side and pH is raised and restored
describe what happens to equilibrium when an alkali is added to a buffer
- provides OH- that react with H+ tp form water
- equilibrium shifts to the right hand side and pH is lowered and restored
give the equation for the buffer system in the blood and explain it
- H2CO3 H+ + HCO3-
- this carbonic acid-hydrogen carbonate equilibrium acts as a buffer to control the pH of the blood
- present in blood plasma to maintain a pH of 7.35-7.45
