5.3.1 Acids, Bases and pH Flashcards
strong acid definition
good proton donator
dissocisate completely to form ions in aqueous solution
monobasic acid definition
1 H+ ion can be replaced per molecule in an acid base reaction
what are H+ ions typically replaced by
metal or ammonium ion
example of monobasic acid
HCl
Dibasic acid
can have 2 protons replaced when they react with bases
example of dibasic acid
H2SO4
what is an acid in terms of protons
proton donor
what is a base in terms of protons
proton acceptor
conjugate acid-base pair
2 species can be interconverted by transfer of a proton
what is pH
measure of how many H+ ions are present in the solution
i.e concentration
pH =
-log[H+(aq)]
[H+]
10^-pH
weak acid definition
poor proton donors, partially dissociate into ion when in solution
where does equilibrium lie for a weak acid and why
HA<-> H+ + A-
lies to the left due to some of the acid not dissociating yet as it only partially dissociates
Ka equation for
HA<-> H+ + A-
[H+][A-] / [HA]
pKa =
-log(Ka)
what is pKa
way of measuring strength of an acid
what type of acid is it if it has a low pKa
stronger acid
strong base
dissociates completely
if you have a low [H+] what pH value would it be
high pH
how many times is the concentration of H+ ions in pH1 than pH2
10 times greater
what would the dilution be to get a solution from pH 1 to pH4
10 x 10 x 10 = 1000
units for [H+]
mol dm-3
what does a larger Ka value show
equilibrium is to the right
the greater the dissociation and the greater the acid strength
what is the Ka and type of acid if the pKa vaue is high
weaker acid
smaller Ka value
what does [H+(aq)] depend on
concentration of acid
acid dissociation constant Ka
what is the acid dissociation curve
Ka
how do you calculate pH from the Ka expression
make [H+] the subject of Ka expression
then use pH = -log[H+]
how to experimentally determine the Ka for a weak acid
- prepare standard solution of the weak acid of known concentration
- measure the pH of the standard solution using pH meter
Ka equation for treating water as a weak acid
[H+][OH-] / [H2O]
what is the ionic product of water
Kw
ions in water multiplied together
definition of an alkali
soluble base that releases OH- ions in aqueous solution
define pH
-log[H+]
what are the assumptions made when using Ka
[HA] doesn’t decrease when partial dissociation occurs - innacurate pH calculation for stronger weak acids
ignores dissociation of water- relevant for very weak acids
how to work out pH for solutions made with acid and base
work out moles of each
find the difference
work out concentration of the difference
do -log[H+]
if the base is in excess then you’ve worked out pOH so then minus that from 14
when working out pH for solution what do you do if one is a dibasicacid
multiply number of moles by 2
