AQA A2 Chemistry Unit 4 Revision

HideShow resource information
  • Created by: S Satish
  • Created on: 18-04-13 16:59
Preview of AQA A2 Chemistry Unit 4 Revision

First 1006 words of the document:

Aci
ds,
Bases
and
Buf
fer
s
Def
ini
ng aci
ds and
bases
A
BronstedLow r
y aci
d i
s a
substance
which
donates
protons
in
a react
ion.
(
a pr
oton donor
).
Aci
ds ar
e subst
ances whi
ch
produce
hydrogen
ions
in
solut
ion.
A
BronstedLow r
y base
is
a subst
ance whi
ch accept
s pr
o t
ons i
n a
react
ion.
(a
prot
o n
accept
or)
.
Bases
are
substances
w hi
ch pr
oduce hydr
oxide
ions
in
solut
ion.
Examples
of
Proton
Transfer
H ydrogen
chlori
de
g as
and ammo ni
a gas
react
t
oge t
her
to
form ammo nium chl
ori
de (
a whi
te
ioni
c sol
id)
HCl
(
g)
+ NH3
(g)
NH4Cl
(
s)
H Cl
+ NH 3 [NH 4+
C l
]
Here t
he hydrogen chl
ori
de
is
acti
ng as an
acid
by donati
ng a
proton
to
ammo ni
a.
A mmo nia
is
acti
ng as
a base by
accepti
ng a
proton.
Acids
a nd
ba ses
can only
react
i
n pai
rs.
A mixt
ure of
concentr
ated sul
ph ur
ic
acid
a nd
concentrat
ed ni
tr
ic
acid
beha ve
as an aci
d base
p ai
r.
H2S O4 +
H NO 3 H 2NO 3+ +
H SO 4
The sul
phuric
acid
don at
es a pr
oton t
o t
h e
nit
ri
c aci
d so
it
i
s act
ing
as t
he acid
w hi
le
the
n i
tr
ic
acid
is
acti
ng as
a base.
Wh et
he r
a
spe ci
es i
s act
ing
as an aci
d or
a base depends
on the
react
an t
s.
Water
as
a n
acid
a nd
a base
H C l
can
don at
e a pr
oton t
o water,
so
that
w at
er act
s as
a base
HC l
+
H 2O H3O + +
C l
H3O +
is
ca l
l
e d
the
o xoni
um ion
Wa t
er may al
so act
as an aci
d
H2O
+ NH 3 OH +
N H4+
Here water
i
s donati
ng a pr
o t
on t
o
ammo ni
a.
The
prot
on
in
aqu eous
soluti
on
T he
H +
ion i
s j
ust
a prot
on. The hydr
o gen
atom has onl
y one
elect
ron and
if
t
h i
s i
s l
ost
all
t
hat
rema i
ns i
s a
prot
o n
(the
hyd r
ogen
nucleus).
T hi
s ext
reme l
y small
si
ze and consequen t
i
ntense
elect
ri
c f
iel
d cause
it
t
o
have unusual
propert
ies
comp ared
w i
th
other
p osi
ti
ve i
ons:
it
i
s never
found i
solated.
I
n aqueous sol
uti
ons i
t
is
always bonded t
o at
l
e ast
one
w at
er
mo lecul
e t
o for
m t
he i
on H3 O+
S i
nce t
h e
H +
has no el
ectrons
of i
ts
ow n,
i
t
can onl
y f
orm a bond
w i
th
a not
her speci
es t
hat has
a l
one pai
r of
electr
ons.
The
ioni
sati
on of
w at
er
Water
i
s sl
i
g ht
ly
ioni
sed H2O H+ +
O H
or
H 2O +
H 2O H 3O+ +
O H
The
equi
li
brium expressi
on
can
be
wri
tt
en as
Kc = [
H +]
[OH ]
/[
H 2O]

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

T he
c oncent
rati
on of
water
i
s constant
and i
s
incorporat
ed i
nto
a mo di
fi
ed equi
li
bri
um con stant
Kw
whe r
e Kw =
Kc x
H 2O.
14
T his
me ans
Kw
(the
ioni
c pr
o duct
of
water)
i
s =
[H+][OH ]
at
298K
and i
s equal
t
o 1
x 10 mo l
2dm 6.…read more

Page 3

Preview of page 3

Page 4

Preview of page 4

Here's a taster:

Ka
=
[H+] /
0.
1 [H+]
[
H+ ]
=
squ are
ro ot
(1.7
x 105 x
0.1)
= 1.
3 x
10 3
mo l
dm 3
pH =
2.89
pKa
F or a
w eak aci
d we of
ten r
efer
to
pKa.
p K a
= l
o g10(Ka)
A l
o we r
val
u e of
pKa suggests
a st
ronger
aci
d.…read more

Page 5

Preview of page 5

Page 6

Preview of page 6

Page 7

Preview of page 7

Here's a taster:

Concentr
a t
ions
an d
volume s
of
reacti
on s
for
aci
d s
and bases
Examp l
e 1
24.
8cm3 of
0.
2 2
mo l
d m 2 sol
uti
on of
B a(
O H)2 ar
e requi
red t
o neut
rali
se
25cm3
of
H Cl.
The r
eacti
on occur
ri
ng
is
2HCl
+
Ba (
O H)2 BaC l
2 +
2H 2O
Moles
of
B a(OH )
2 = 24.
8
x 0.…read more

Page 8

Preview of page 8

Here's a taster:

Examp l
e 2
Calcul
ate
the pH i
n t
he ti
tr
ati
on of
16cm3 of
0.16mo l
dm 3
solut
ion
of
N aOH
at
the
po i
nt
w hen
12cm3
of
0.1
mo ldm 3
solut
ion
of
H2S O4 have been added.
The aci
d:
base stoi
chiometry
is
1:2
Moles
o f
OH =
16
x 0.
16 /
1000 = 0.
00 256
mo l
Moles
o f
H+ added =
2
x 12
x 0.…read more

Page 9

Preview of page 9

Page 10

Preview of page 10

Comments

Annabel

WOW this is amazing!

Aysha Aslam

These notes are absolutley amazing!! Thank you so much

asha


Thanks for these notes, they are really good.

lalalalayla

Absolutely perfect. Thank you so much. You're the best XD

Kate

I wish I'd found this before I had 4 days left haha

Similar Chemistry resources:

See all Chemistry resources »See all resources »