CALCULATIONS
INVOLVING FORMULAE
A guide for GCSE students
2010
KNOCKHARDY PUBLISHING
SPECIFICATIONS
CALCULATIONS INVOLVING FORMULAE
INTRODUCTION
This Powerpoint show is one of several produced to help students
understand selected GCSE Chemistry topics. It is based on the requirements
of the AQA specification but is suitable for other examination boards.
Individual students may use the material at home for revision purposes and
it can also prove useful for classroom teaching with an interactive white
board.
Accompanying notes on this, and the full range of AS and A2 Chemistry
topics, are available from the KNOCKHARDY WEBSITE at...
www.knockhardy.org.uk
All diagrams, photographs and any animations in this Powerpoint are
original and created by Jonathan Hopton. Permission must be
obtained for their use in any work that is distributed for financial gain.
HOPTON
CALCULATIONS INVOLVING FORMULAE
CONTENTS
• Working out simple formulae
• Relative formula mass
• Percentage composition
• Reacting masses
• Yield and percentage yield
HOPTON
SOME COMMON FORMULAE
chlorine gas
hydrogen gas
nitrogen gas
oxygen gas
hydrochloric acid
nitric acid
sulphuric acid
sodium hydroxide
sodium chloride
sodium carbonate
potassium chloride
magnesium oxide
magnesium hydroxide
magnesium carbonate
magnesium sulphate
calcium carbonate
calcium chloride
Cl2
H2
N2
O2
HCl
HNO3
H2SO4
NaOH
NaCl
Na2CO3
KCl
MgO
Mg(OH)2
MgCO3
MgSO4
CaCO3
CaCl2
HOPTON
Many formulae can be
worked out by reference
to a table of ions.
Others just have to be
known off by heart.
TABLE OF IONS
hydrogen
sodium
potassium
lithium
rubidium
caesium
silver(I)
ammonium
H+
Na+
K+
Li+
Rb+
Cs+
Ag+
NH4+
chloride
bromide
iodide
hydroxide
nitrate
nitrite
hydrogencarbonate
hydrogensulphate
Cl¯
Br¯
I¯
OH¯
NO3¯
NO2¯
HCO3¯
HSO4¯
calcium
barium
magnesium
zinc
iron(II) “ferrous”
copper(II)
Ca2+
Ba2+
Mg2+
Zn2+
Fe2+
Cu2+
sulphate
sulphite
sulphide
oxide
carbonate
SO42SO32S2O2CO32-
aluminium
iron(III) “ferric”
Al3+
Fe3+
HOPTON
TABLE OF IONS
hydrogen
sodium
potassium
lithium
rubidium
caesium
silver(I)
ammonium
H+
Na+
K+
Li+
Rb+
Cs+
Ag+
NH4+
chloride
bromide
iodide
hydroxide
nitrate
nitrite
hydrogencarbonate
hydrogensulphate
Cl¯
Br¯
I¯
OH¯
NO3¯
NO2¯
HCO3¯
HSO4¯
calcium
barium
magnesium
zinc
iron(II) “ferrous”
copper(II)
Ca2+
Ba2+
Mg2+
Zn2+
Fe2+
Cu2+
sulphate
sulphite
sulphide
oxide
carbonate
SO42SO32S2O2CO32-
aluminium
iron(III) “ferric”
Al3+
Fe3+
NUMBER OF ELECTRONS IN
OUTER SHELL OF ATOMS
1
HOPTON
2
3
6
7
TABLE OF IONS
hydrogen
sodium
potassium
lithium
rubidium
caesium
silver(I)
ammonium
H+
Na+
K+
Li+
Rb+
Cs+
Ag+
NH4+
chloride
bromide
iodide
hydroxide
nitrate
nitrite
hydrogencarbonate
hydrogensulphate
Cl¯
Br¯
I¯
OH¯
NO3¯
NO2¯
HCO3¯
HSO4¯
calcium
barium
magnesium
zinc
iron(II) “ferrous”
copper(II)
Ca2+
Ba2+
Mg2+
Zn2+
Fe2+
Cu2+
sulphate
sulphite
sulphide
oxide
carbonate
SO42SO32S2O2CO32-
aluminium
iron(III) “ferric”
Al3+
Fe3+
Formulae can be worked out by
balancing the charges so that…
negative charge = positive charge
HOPTON
CONSTRUCTING FORMULAE
HOPTON
CONSTRUCTING FORMULAE
Many formulae can be worked out
by balancing the charges so that…
negative charge = positive charge
HOPTON
CONSTRUCTING FORMULAE
Q.1
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
sodium ion
chloride ion
HOPTON
Na+
Cl¯
CONSTRUCTING FORMULAE
Q.1
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
sodium ion
chloride ion
Na+
HOPTON
Na+
Cl¯
Cl¯
CONSTRUCTING FORMULAE
Q.1
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
Na+
Cl¯
sodium ion
chloride ion
Na+
Cl¯
ONE Na+ balances ONE Cl¯
FORMULA is
HOPTON
NaCl
CONSTRUCTING FORMULAE
Q.2
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
magnesium ion
sulphate ion
NaCl
Mg2+
SO42-
Mg2+
HOPTON
SO42-
CONSTRUCTING FORMULAE
Q.2
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
magnesium ion
sulphate ion
NaCl
Mg2+
SO42-
Mg2+
SO42-
ONE Mg2+ balances ONE SO42FORMULA is
HOPTON
MgSO4
CONSTRUCTING FORMULAE
Q.3
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K+
potassium ion
oxide ion
K+
O2-
K+
HOPTON
O2-
CONSTRUCTING FORMULAE
Q.3
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K+
potassium ion
oxide ion
K+
O2-
K+
O2-
TWO K+ balance ONE O2FORMULA is
HOPTON
K2O
CONSTRUCTING FORMULAE
Q.4
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K2O
Cl¯
calcium ion
chloride ion
Ca2+
Cl¯
Ca2+
HOPTON
Cl¯
CONSTRUCTING FORMULAE
Q.4
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K2O
Cl¯
calcium ion
chloride ion
Ca2+
Cl¯
Ca2+
Cl¯
ONE Ca2+ balances TWO Cl¯
FORMULA is
HOPTON
CaCl2
CONSTRUCTING FORMULAE
Q.5
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K2O
CaCl2
NO3¯
copper(II) ion
nitrate ion
Cu2+
NO3¯
Cu2+
HOPTON
NO3¯
CONSTRUCTING FORMULAE
Q.5
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K2O
CaCl2
NO3¯
copper(II) ion
nitrate ion
Cu2+
NO3¯
Cu2+
NO3¯
ONE Cu2+ balances TWO NO3¯
FORMULA is
HOPTON
Cu(NO3)2
CONSTRUCTING FORMULAE
Q.5
Write out the correct formula for each of the following compounds.
a) sodium chloride
b) magnesium sulphate
c) potassium oxide
d) calcium chloride
e) copper(II) nitrate
NaCl
MgSO4
K2O
CaCl2
NO3¯
Cu2+
NO3¯
copper(II) ion
nitrate ion
Cu2+
NO3¯
NOTE THE BRACKETS
If the brackets weren’t there, the formula
would appear as CuNO32 (thirty two
oxygens). Brackets are used when the
ion has more than one element in it.
eg
NO3¯
OH¯
ONE Cu2+ balances TWO NO3¯
FORMULA is
NH4+
HOPTON
Cu(NO3)2
FORMULAE – Test questions
Write out the correct formula for each of the following compounds.
a) lithium chloride
b) calcium sulphate
c) sodium oxide
d) calcium chloride
e) iron(II) nitrate
f) potassium sulphate
g) calcium hydroxide
h) zinc carbonate
i) aluminium oxide
j) aluminium sulphate
k) ammonium nitrate
l) ammonium chloride
m) ammonium sulphate
n) iron(III) chloride
LiCl
CaSO4
Na2O
CaCl2
Fe(NO3)2
K2SO4
Ca(OH)2
ZnCO3
Al2O3
Al2(SO4)3
NH4NO3
NH4Cl
(NH4)2SO4
FeCl3
HOPTON
FORMULAE – Test questions
Write out the correct formula for each of the following compounds.
a) lithium chloride
b) calcium sulphate
c) sodium oxide
d) calcium chloride
e) iron(II) nitrate
f) potassium sulphate
g) calcium hydroxide
h) zinc carbonate
i) aluminium oxide
j) aluminium sulphate
k) ammonium nitrate
l) ammonium chloride
m) ammonium sulphate
n) iron(III) chloride
LiCl
CaSO4
Na2O
CaCl2
Fe(NO3)2
K2SO4
Ca(OH)2
ZnCO3
Al2O3
Al2(SO4)3
NH4NO3
NH4Cl
(NH4)2SO4
FeCl3
HOPTON
RELATIVE FORMULA MASS
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
To calculate this value, it is important that one understands how
to work out the number of each type of atom present.
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
To calculate this value, it is important that one understands how
to work out the number of each type of atom present.
A small subscript number tells you how many there of the atom
just before the subscript
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
To calculate this value, it is important that one understands how
to work out the number of each type of atom present.
A small subscript number tells you how many there of the atom
just before the subscript
H2O
2 hydrogen atoms
1 oxygen atom (a 1 after the O is unnecessary)
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
To calculate this value, it is important that one understands how
to work out the number of each type of atom present.
A small subscript number tells you how many there of the atom
just before the subscript
H2O
Ca(OH)2
2 hydrogen atoms
1 oxygen atom (a 1 after the O is unnecessary)
1 calcium atom
2 lots of everything in the bracket
ie 2 oxygen atoms and 2 hydrogen atoms
(groups of atoms occurring in brackets include… SO4 NO3 NH4 OH)
HOPTON
RELATIVE FORMULA MASS
HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?
a) H2O
b) NaOH
c) (NH4)2SO4
d) Ca(OH)2
e) H2SO4
f) CuSO4.5H2O
2xH
1 x Na
2xN
1 x Ca
2xH
1 x Cu
HOPTON
1xO
1xO
4xO
2xO
4xO
10 x H
1xH
8xH
2xH
1xS
9xO
1xS
1xS
RELATIVE FORMULA MASS
HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?
a) H2O
b) NaOH
c) (NH4)2SO4
d) Ca(OH)2
e) H2SO4
f) CuSO4.5H2O
2xH
1 x Na
2xN
1 x Ca
2xH
1 x Cu
HOPTON
1xO
1xO
4xO
2xO
4xO
10 x H
1xH
8xH
2xH
1xS
9xO
1xS
1xS
RELATIVE FORMULA MASS
HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?
a) H2O
b) NaOH
c) (NH4)2SO4
d) Ca(OH)2
e) H2SO4
f) CuSO4.5H2O
2xH
1 x Na
2xN
1 x Ca
2xH
1 x Cu
1xO
1xO
4xO
2xO
4xO
10 x H
1xH
8xH
2xH
1xS
9xO
1xS
1xS
A NUMBER IN THE FRONT OF A FORMULA
MULTIPLIES EVERYTHING IN THAT FORMULA
HOPTON
RELATIVE FORMULA MASS
HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?
a) H2O
b) NaOH
c) (NH4)2SO4
d) Ca(OH)2
e) H2SO4
f) CuSO4.5H2O
2xH
1 x Na
2xN
1 x Ca
2xH
1 x Cu
1xO
1xO
4xO
2xO
4xO
10 x H
1xH
8xH
2xH
1xS
9xO
1xS
1xS
A NUMBER IN THE FRONT OF A FORMULA
MULTIPLIES EVERYTHING IN THAT FORMULA
g) 2 NaOH
h) 3 Ca(OH)2
i) 2 Na2HPO4
2 x Na 2 x O
3 x Ca 6 x O
4 x Na 8 x O
HOPTON
2xH
6xH
2xH
2xP
RELATIVE FORMULA MASS
HOW MANY ATOMS OF EACH TYPE ARE IN THE FOLLOWING?
a) H2O
b) NaOH
c) (NH4)2SO4
d) Ca(OH)2
e) H2SO4
f) CuSO4.5H2O
2xH
1 x Na
2xN
1 x Ca
2xH
1 x Cu
1xO
1xO
4xO
2xO
4xO
10 x H
1xH
8xH
2xH
1xS
9xO
1xS
1xS
A NUMBER IN THE FRONT OF A FORMULA
MULTIPLIES EVERYTHING IN THAT FORMULA
g) 2 NaOH
h) 3 Ca(OH)2
i) 2 Na2HPO4
2 x Na 2 x O
3 x Ca 6 x O
4 x Na 8 x O
HOPTON
2xH
6xH
2xH
2xP
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
HOPTON
HOPTON
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
H
+
H
+
O
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
H
1
+
+
H
1
+
+
O
16
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
= 18
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
H
1
+
+
H
1
+
+
O
16
Copper CuSO4
sulphate
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
= 18
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
O
16
Cu
+
S
+
4xO
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
= 18
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
= 18
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
= 18
= 160
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
Calcium Ca(OH)2
hydroxide
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
Calcium Ca(OH)2 Ca
+
2 lots of OH
hydroxide
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
Calcium Ca(OH)2 Ca
+
2 lots of OH
hydroxide
Ca
+ O +H + O + H
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
Calcium Ca(OH)2 Ca
+
2 lots of OH
hydroxide
Ca
+ O +H + O + H
40
16 + 1
+ 16 + 1
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
The relative formula mass is the sum of the relative atomic masses of
ALL the atoms present in the formula
Water
H2O
Copper CuSO4
sulphate
H
1
+
+
H
1
+
+
Cu
64
+
+
S
32
+
+
O
16
4xO
4 x 16
= 18
= 160
TAKE CARE WHEN THERE ARE BRACKETS
Calcium Ca(OH)2 Ca
+
2 lots of OH
hydroxide
Ca
+ O +H + O + H
40
16 + 1
+ 16 + 1
= 74
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
Use the list of relative atomic masses to calculate the relative formula
mass of the following compounds
H2
O2
H2O
NaOH
CH4
C5H12
NaCl
H2SO4
Na2SO4
CaCl2
CaCO3
NH4NO3
CuSO4
Al2O3
Ca(OH)2
Al2(SO4)3
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
RELATIVE FORMULA MASS
Use the list of relative atomic masses to calculate the relative formula
mass of the following compounds
H2
2
O2
32
H2O
16
C5H12
18
NaOH
40
CH4
NaCl
36.5
H2SO4 98
Na2SO4
142
CaCl2
111
CaCO3 100
NH4NO3
80
CuSO4
160
Al2O3
102
72
Ca(OH)2 74
Al2(SO4)3 342
H = 1; C = 12; N = 14; O = 16; Na = 23; Mg = 24; Al = 27;
S = 32; Cl = 35.5; K = 39; HOPTON
Ca = 40; Fe = 56; Cu = 64
PERCENTAGE COMPOSITION
HOPTON
PERCENTAGE COMPOSITION
It can be quite useful to know how much of an element is present in a
compound.
This is not how many atoms there are BUT what mass is present.
This has some relevance when considering how much metal is in a
particular ore.
HOPTON
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
HOPTON
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
HOPTON
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
HOPTON
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
2 Calculate how much of this is Fe
56 + 56
HOPTON
= 112
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
2 Calculate how much of this is Fe
56 + 56
3 Calculate the fraction that is Fe
112
160
HOPTON
= 112
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
2 Calculate how much of this is Fe
56 + 56
3 Calculate the fraction that is Fe
112
160
4 Calculate the percentage that is Fe
112 x 100
160
HOPTON
= 112
=
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
2 Calculate how much of this is Fe
56 + 56
3 Calculate the fraction that is Fe
112
160
4 Calculate the percentage that is Fe
112 x 100
160
HOPTON
= 112
= 70.0%
PERCENTAGE COMPOSITION
Metal ores do not just contain a metal, there are other elements present.
eg Fe2O3, TiO2, ZnS.
To calculate the PERCENTAGE BY MASS of a metal in an ore;
1 Calculate the formula mass (Fe2O3)
56 + 56 + 16 + 16 + 16 = 160
2 Calculate how much of this is Fe
56 + 56
3 Calculate the fraction that is Fe
112
160
4 Calculate the percentage that is Fe
112 x 100
160
Calculate the percentage of each metal in… Al2O3
ZnS
HOPTON
= 112
= 70.0%
TiO2
NaCl
CuFeS2
REACTING MASSES
HOPTON
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
HOPTON
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
copper
oxide
+
sulphuric acid

copper
sulphate
Write out a word equation.
HOPTON
+
water
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
copper
oxide
+
sulphuric acid

copper
sulphate
CuO
+
H2SO4

CuSO4
+
+
water
H2O
Write out a proper equation showing the correct formulae.
HOPTON
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
copper
oxide
+
sulphuric acid

copper
sulphate
CuO
+
H2SO4

CuSO4
64 + 16
(1x1) + 32 + (4x16)
+
+
64 + 32 + (4x16)
water
H2O
(2x1) + 16
Look up the atomic masses in a table and work out the
formula mass of each chemical in the equation.
HOPTON
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
copper
oxide
+
sulphuric acid

copper
sulphate
CuO
+
H2SO4

CuSO4
64 + 16
80
(1x1) + 32 + (4x16)
98
+
+
64 + 32 + (4x16)
160
water
H2O
(2x1) + 16
18
Look up the atomic masses in a table and work out the
formula mass of each chemical in the equation.
HOPTON
REACTING MASSES
The masses of all the atoms at the end of a reaction (THE PRODUCTS)
must equal the masses of all the atoms at the start of the reaction
(THE REACTANTS).
copper
oxide
+
sulphuric acid

copper
sulphate
CuO
+
H2SO4

CuSO4
64 + 16
(1x1) + 32 + (4x16)
80
98
+
water
+
64 + 32 + (4x16)
H2O
(2x1) + 16
160
178
18
178
This shows that the masses after the reaction
are the same as the masses before.
HOPTON
YIELD AND PERCENTAGE YIELD
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get. (assuming 100% conversion)
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98
HOPTON

CuSO4
160
+
H 2O
18
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO + H2SO4
 CuSO4 + H2O
80
98
160
18
If you start with 80g of copper oxide, you can
get a maximum of 160g of copper sulphate.
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO + H2SO4
 CuSO4 + H2O
80
98
160
18
If you start with 80g of copper oxide, you can
get a maximum of 160g of copper sulphate.
Q. What is the maximum yield of copper sulphate if you
start with a) 20g of copper oxide
b) 400g of copper oxide
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO + H2SO4
 CuSO4 + H2O
80
98
160
18
If you start with 80g of copper oxide, you can
get a maximum of 160g of copper sulphate.
Q. What is the maximum yield of copper sulphate if you
start with a) 20g of copper oxide
Ans. 40g
b) 400g of copper oxide
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO + H2SO4
 CuSO4 + H2O
80
98
160
18
If you start with 80g of copper oxide, you can
get a maximum of 160g of copper sulphate.
Q. What is the maximum yield of copper sulphate if you
start with a) 20g of copper oxide
Ans. 40g
b) 400g of copper oxide
Ans. 800g
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
80g should give a maximum of 160g.
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
80g should give a maximum of 160g. However only 120g
are produced.
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
80g should give a maximum of 160g. However only 120g
are produced. The fraction produced is 120/160 = ¾ (0.75).
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
80g should give a maximum of 160g. However only 120g
are produced. The fraction produced is 120/160 = ¾ (0.75).
Multiply by 100 to get the percentage.
HOPTON
YIELD AND PERCENTAGE YIELD
YIELD
How much of a chemical you get
from a reaction.
PERCENTAGE
YIELD
How much of a chemical you get
COMPARED WITH how much you
should get.
Example
CuO
80
+
H2SO4
98

CuSO4
160
+
H 2O
18
Q. If you start with 80g of copper oxide and only get 120g of
copper sulphate, what is the percentage yield?
80g should give a maximum of 160g. However only 120g
are produced. The fraction produced is 120/160 = ¾ (0.75).
Multiply by 100 to get the percentage. ANS 75% yield
HOPTON
CALCULATIONS
INVOLVING FORMULAE
THE END
©2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING