Pages in this set

Page 1

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11/12/2011





Moles,
calcula/ons
in
gaseous

and
solu/on
and
acids
and
bases





Moles
and
calcula/ons





1

Page 2

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11/12/2011





Objec/ves

All


Define
rela/ve
molecular
mass
and
rela/ve
formula
mass


Most

Describe
Avogadro's
constant
and
the
terms
moles
and

molar
mass



Some


Explain
how
to
use
moles
and
molar
mass
in
calcula/ons






Rela/ve
molecular
mass
(Mr)


When
we
are
referring
to
a
compound
we
add
up
the

rela/ve
atomic…

Page 3

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11/12/2011





Worked
example

H2O
=
(2x1)
+
16
=
18

CH4
=
12
+
(4x1)
=
16



Where
crystals
are
concerned
the
Mr
may
also

include
water
of
crystallisa/on.







Calcula/ng
Mr

Calculate
the
Mr
of;

1. CuSO4

2. PbNO3

3. Na2CO3.10H2O





3

Page 4

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11/12/2011





Rela/ve
formula
mass


Ionic
compounds
consist
of
metal
and
non-metal

ions
rather
than
molecules


e.g.
NaCl
is
made
up
of
Na+
and
Cl-
ions
in
a
la[ce.

It
would
not
be
correct
to
use
the
term
rela/ve

molecular
mass
as
an
NaCl
molecule
does
not
exist.

To
be
absolutely…

Page 5

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11/12/2011





The
Mole

· 1
mole
is
the
amount
of
substance
which

contains
as
many
par/cles
as
there
are
atoms

in
exactly
12
grams
of
12C.



· This
value
is
6.022
x
1023
par:cles.


· For
an
element
it
is
the


· For
a
compound
it
is
the








Molar
Mass…

Page 6

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11/12/2011





Molar
mass
example

Water
molecules
have
Mr
=
18.



therefore
1
mole
of
water
has
a
mass
of
18

grams.










Calcula/ng
number
of
moles

Number
of
moles
(mol)
=

mass
(g)














molar
mass
(gmol-1)



This
equa/on
can
be
rearranged
to
calculate
mass
or

molar
mass
as
well
as
number…

Page 7

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11/12/2011





Worked
Example

· How
many
moles
of
Ca
are
there
in
120g
of

Ca?



Ar
Ca
=
40,
therefore
molar
mass
Ca
=
40
gmol-1




number
of
moles
=


120




















40












=
3.0
mol







7

Page 8

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11/12/2011





Mark
scheme





AfL
­
using
whiteboards

Calculate
the
amount
in
moles
in
the
following;

1. 32.1
grams
of
sulfur
atoms

2. 50.0
grams
of
CaCO3

3. 6.35
grams
of
copper
atoms

4. 400
grams
of
NaOH

5. 69g
of
Pb

6. 5.30g
of
Na2CO3







8

Page 9

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11/12/2011





Calcula/ng
masses

Worked
example

What
mass
of
NaCl
contains
10
moles
of
NaCl
par/cles?




Mr
NaCl
=
23
+
35.5
=
58.5
gmol-1





Mass
=
moles
x
Mr


Mass
=
10
x
58.5
=
585
grams














AfL
­
using
whiteboards

Calculate
the
mass
of


1. 0.013
moles
of
Cl2…

Page 10

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11/12/2011





Past
paper
ques/on





Mark
scheme





10

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