acids and bases Flashcards
what is an acid
a proton donor
what is a base
a proton acceptor
acid + bases involves what
the transfer of protons
pH =
log [H+]
if it is Mg(OH)2 have to multiply by 2
[H+] =
10^-pH
why do you use ph scale / log scale
because [H+] in aqueous solution covers a wide range
what is Kw
the ionic product of water
what can you assume about H2O with kw
conc of H2O is very high and H2O is. effectively constant
what is the effect of temp on ph of water
as temp increases equilibrium moves right to oppose the increase in temp therefor conc H+ and conc OH- increases therefore Kw increases and therefore pH decreases however the water is still neutral
what is the definition of water
[H+]=[OH-]
what is the kw you need to remember
Kw= 10^-14 at 298K
what is Kw equation
[H+][OH-]
what are the Ka equations
ka=[H+][A-]/[HA]
Ka=[H+]^2/[HA]
pka =
log ka
ka =
10^-pka
what is ka dependent on
temperature
in a solution of weak acid and water link [H+] and [A-]
[H+]=[A-]
at equilibrium what is [H+] =
[HA] at initial
what is ka
dissosciation constant for weak acid
what is a buffer solution and what does it do
a solution where the ph doesnt change significantly when small amounts of acids or alkali is added
what do buffers contain
a mixture of weak acid and weak base so the mixture can react with either acid or base, equilibria will then change in response to this change in moles
why do acid and bases need to be weak in a buffer
to be in equilibrium
what does an acidic buffer solution contain
a weak acid and a salt of that weak acid
what does a basic buffer solution contain
a weak base and a salt of that weak base
what does a strong acid and strong base titration curve look like
what does a strong acid and weak base titration curve look like
what does a weak acid and strong base titration curve look like
what does a weak acid and weak base titration curve look like
what is an aliquot
a small specific amount of volume added each time
where is the neutralisation point on a titration graph
when the ph is 7
where is the end point on a titration graph
when the graph ends
where is the equivalence point on a titration graph
half way up the vertical part of the graph
where do you start the curve/graph
at the ph of the thing that is in the conical flask e.g. if theres a strong acid in the conical flask you start the curve at ph 1/2
how much indicator do you use
a small amount of indicator
why do you use a small amount of indicator
as they are acids you have to use a small amounts to avoid missing the end points
when does the indicator need to change
over the range of the equivalance
why cant you choose a good indicator for weak acid and weak base
it changes so fast its impossible to find a good indicator
what indicator do you use for strong acid and strong base
either methyl orange or phenolphthalein
what indicator do you use for strong acid and weak base
methyl orange
what indicator do you use for weak acid and strong base
phenolphthalein
where is the buffer region
in the two horizontal bits of the graph
where is the half equivalence point
when half of the equivalence point volume has been used
what is equal at the half equivalance point
ph=pka
what happens at 1/2 equivalance point
1/2 eq point is when in proportion 1/2 moles acid has reacted with 1/2 moles base
what is the 1/2 eq point model answer calculation
[HA]=[A-] so cancel
Ka= [H+][A-]/[HA]
Ka= [H+]
-logka = -log[H+]
therefore pka = ph
calculations : strong acid
([acid] to get [H+]) x number of H+ ions —-> pH = -log[H+]
calculations : strong base
([base] to get [OH]) x number of H+ ions —-> kw=[H+][OH-] —-> pH = -log[H+]
calculation : pure water in question
[H+]=[OH] (for pure h2o) —-> Kw= [H+]^2 —-> pH = -log[H+]
calculation : pure weak acid in question
[H+]=[A-] (for pure weak acid) —-> ka=[H+]^2/[HA] —-> pH = -log[H+]
buffer made —-> mixture of weak acid and base —-> moles of weak acid in excess —-> YES
OH-+HA -> A-+H20 —-> find moles of HA and A- —-> [H+] = ka[HA]/[A-] —-> ph = -log[H+]
buffer made —-> mixture of weak acid and base —-> moles of weak acid in excess —-> NO
find moles of strong base left —-> do strong base method
buffer made —-> NO mixture of weak acid and base —-> mixture of weak acid and salt
find moles of HA and A- —-> find [H+] from [A-]-ka([HA]/[A-]) —-> ph=-log[H+]
