acids, bases, buffers Flashcards
write an expression for how to calculate pH
pH = - log [H+]
explain how to calculate the pH of a strong acid
concentration of acid = [H+] because it is fully dissociated in water
what are the assumptions made in the calculation of a strong acid
the acid is full dissociated
[acid] = [H+]
explain how to calculate [H+] from a given pH
[H+] = 10 to power of -pH
define bronsted lowry acid
proton donor
define bronsted lowry base
proton acceptor
explain the difference between a weak and strong acid
strong acids are fully dissociated in water, weak acids only partially dissociate in water
write the equation for the reaction of a strong acid with water
HA + H2O –> H3O+ + A-
write an equation for the reaction of a weak acid with water
HA + H20 ⇌ H3O+ + A-
explain how to calculate [H+] for H2SO4
2 x concentration of acid = [H+] because its diprotic
write an expression for the ionic product of water (Kw)
Kw = [H+] [OH-]
modify Kw to calculate the pH of pure water
Kw = [H+] squared
what assumption is made in the calculation of pH of pure water
that each water molecule dissociates to give H+ and OH-
explain how to calculate pH of a strong base
assume concentration of base is equal to [OH-] concentration , then use the Kw expression
explain how to calculate [OH-] of barium hydroxide
Ba(OH)2 therefore 2x the concentration of BaOH2 = [OH-]
explain why pure water is always neutral regardless of the pH
[H+] = [OH-] at any temperature
for an acid [H+] > [OH-]
for a base [H+] < [OH-]
calculate pKa
pKa = - log Ka
calculate Ka from pKa
Ka = 10 to power of -pKa
write an expression for Ka
Ka = [H+] [A-] / [HA]
define a buffer solution
a solution that resists the change in pH when a small amount of acid or alkali are added
write a modified expression for Ka when doing buffer calculation
Ka = [H+] x (salt/acid)
how do you make a buffer
mixture of a weak acid and it’s sodium salt
what happens to the reaction of
HA reversible reaction arrow when NaOH is added when a buffer is present
H+ + OH- —> H2O
concentration of H+ ions decreases therefore equilibrium shifts to right
no change in pH
write an equation for the disassociation of a weak acid HA
HA ⇌ H+ + A-
what happens if HCl is added to this reaction:
HA ⇌ H+ + A-
H+ concentration increases
equilibrium shifts to left to oppose the change
A- is needed to react with H+ but conc is very small is runs out quickly
what happens when NaOH is added to weak acid HA that has a buffer
buffers equilibrium by shifting it right
what happens if HCl is added to weak acid HA
cannot buffer
not enough A- for equilibrium to shift left
