21 acids and bases Flashcards
define acid
proton donor
define base
proton acceptor
define a strong acid
an acid that fully dissociates
define a weak acid
an acid that only partially dissociates
define pH
-log10[H+]
how do you calculate the concentration of H+ ([H+]) from pH?
10^-pH
what does Kw mean?
the ionic product of water
define Kw
[H+][OH-]
1x10^-14
what is a monoprotic acid?
one which only releases one H+ ion
what is a diprotic acid?
one which releases two H+ ions
if the pH is small, what does that mean in terms of concentration of H+ ions?
greater concentration of H+ ions
name 4 strong acids
HCl (hydrochloric acid)
H2SO4 (sulfuric acid)
HNO3 (nitric acid)
H3PO4 (phosphoric acid)
how does HCl dissociate?
give an equation
fully dissociates
HCl –> H+ + Cl-
where does the equilibrium lie in equations of strong acid dissociations?
entirely to the right
if the concentration of HCl is originally 2moldm-3, what will be the conc of H+ once fully dissociated?
2moldm-3
if the concentration of H2SO4 is originally 2moldm-3, what will be the conc of H+ once fully dissociated?
4moldm-3
how does a weak acid dissociate?
give an equation in terms of HA
partially dissociates
HA <–> H+ + A-
where does the equilibrium lie in equations of weak acid dissociations?
on the left hand side
write a Ka expression for the dissociation of weak acid HA
Ka = [H+][A-]/[HA]
how would you find the concentration of H+ in a weak acid dissociation?
[H+] = [A-]
Ka = [H+]^2/[HA]
[H+]^2 = Ka x [HA]
[H+] = √Ka x [HA]
how do you calculate pKa?
-log10Ka
how do you find Ka from pKa?
10^-pKa
write an equation for the ionisation of water
H2O <–> H+ + OH-
where does the equilibrium lie in the equations for the ionisation of water?
very far left
what is the value of Kw?
1x10^-14 mol2dm-6
give the expression of Kw
Kw = [H+][OH-]
what affects the value of Kw?
temperature
why is pure water always neutral?
because [H+[ and [OH-] are equal at all times
how would you calculate the concentration of pure water?
H2O <–> H+ + OH-
[H+] = [OH-]
[H+]^2 = Kw
[H+] = √Kw
is the forward reaction of water dissociation endothermic or exothermic?
endothermic
why does [H+] = 1x10^-7 moldm-3 at 298K?
√1x10^-14 = 1x10^-7
which way does equilibrium shift when temperature increases in water dissociation?
shifts to the right in the endothermic direction to oppose the increase in temperature
when a strong base reacts with an acid what does it form?
water
use NaOH to write an equation to show how a strong base dissociates
NaOH –> Na+ + OH-
where does the equilibrium lie in a strong base dissociation?
entirely to the right
how would you calculate the [H+] in a strong alkali? (use NaOH)
[NaOH] = [OH-]
Kw = [OH-][H+]
[H+] = Kw/[OH-]
define buffer
a solution that can resist changes in pH when a small amount of acid or base is added
what is an acidic buffer?
made of a weak acid and a soluble salt of that acid. maintains a pH below 7
what is a basic buffer?
made of weak base and a soluble salt of that base. maintains a pH over 7
why can buffers only cope with small amounts of acids or bases being added?
because can they can become too saturated
how would you calculate [H+] in an acidic buffer solution if you are given the concentration of the acid and the salt?
- construct an equation for the weak acid.
- construct a Ka expression for the weak acid.
- substitute the values into the expression (HA is the acid A- is the salt)
- rearrange the equation to find [H+]
how would you calculate [H+] in an acidic buffer solution if you are given the concentration and the volumes of the reactants?
- construct a neutralisation reaction.
- complete an ICE box to figure out the moles
- construct a Ka expression for the dissociation of the acid.
- rearrange the equation.
