Download Igcse chemistry lesson 2

IGCSE CHEMISTRY LESSON 2
Section 1
Principles
of
Chemistry
a)
b)
c)
d)
e)
f)
g)
h)
i)
States of matter
Atoms
Atomic structure
Relative formula mass
Chemical formulae and
chemical equations
Ionic compounds
Covalent substances
Metallic crystals
Electrolysis
Lesson 2
a) Relative
formula
mass
b) Chemical
formulae
and
Chemical
equations
1.15 calculate relative formula masses
(Mr) from relative atomic masses (Ar)
1.16 understand the use of the term mole
to represent the amount of substance
1.17 carry out mole calculations using
relative atomic mass (Ar) and relative
formula mass (Mr).
What is RELATIVE ATOMIC MASS?
By definition: “mass of a particular atom
compared to the mass of an atom of hydrogen”
Relative atomic mass is also the same as the
mass number – it’s that simple!
Relative Atomic Mass and Atomic Number
Relative Atomic
Mass
= total number of protons
and neutrons
23
ATOMIC NUMBER
11
= number of protons (also
electrons)
Na
Relative atomic mass is always bigger than the atomic
number
Look up the Mass Numbers of the
following elements:
Oxygen
Carbon
Iron
Lead
Iodine
Helium
Nitrogen
Copper
Calcium
Tin
Look up the Mass Numbers of the
following elements:
Oxygen
16
Carbon
12
Iron
56
Lead
207
Iodine
127
Helium
4
Nitrogen
14
Copper
63.5
Calcium
40
Tin
119
When atoms join together to form a
compound (eg. Magnesium oxide) we can
calculate the RELATIVE FORMULA MASS:
When atoms join together to form a
compound (eg. Magnesium oxide) we can
calculate the RELATIVE FORMULA MASS:
Magnesium oxide
MgO
24 + 16
= 40
Chemical formulae
MgO
Chemical formulae
MgO
1 Mg, 1 O
Chemical formulae
MgO
1 Mg, 1 O
H2SO4
Chemical formulae
MgO
H2SO4
1 Mg, 1 O
2H, 1 S, 4 O
Chemical formulae
MgO
H2SO4
1 Mg, 1 O
2H, 1 S, 4 O
Ca(OH)2
Chemical formulae
MgO
H2SO4
1 Mg, 1 O
2H, 1 S, 4 O
Ca(OH)2
1 Ca, 2 O, 2 H
Chemical formulae
MgO
H2SO4
1 Mg, 1 O
2H, 1 S, 4 O
Ca(OH)2
2Na2CO3
1 Ca, 2 O, 2 H
Chemical formulae
MgO
H2SO4
1 Mg, 1 O
2H, 1 S, 4 O
Ca(OH)2
2Na2CO3
1 Ca, 2 O, 2 H
4 Na, 2 C, 6 O
When atoms join together to form a
compound (eg. Magnesium oxide) we can
calculate the RELATIVE FORMULA MASS:
Magnesium oxide
MgO
24 + 16
= 40
Now calculate the Relative Formula Mass for
the following compounds:
Now calculate the Relative Formula Mass for
the following compounds:
Compound
Formula
Calcium oxide
CaO
Sulphuric acid
H2SO4
Sodium nitrate
NaNO3
Aluminium
hydroxide
Al(OH)3
Lead carbonate
PbCO3
Relative formula
mass
Now calculate the Relative Formula Mass for
the following compounds:
Compound
Formula
Relative formula
mass
Calcium oxide
CaO
40 + 16 = 56
Sulphuric acid
H2SO4
2 + 32 + 64 = 98
Sodium nitrate
NaNO3
23 + 14 + 48 = 85
Aluminium
hydroxide
Al(OH)3
27 + 48 + 3 = 78
Lead carbonate
PbCO3
207 + 12 + 48 = 267
Relative Atomic Mass
Be
aware!
Ar
Relative Atomic Mass
Be
aware!
Ar
Relative Formula Mass
Mr
The mole
The mole
You may think
that the mole is
a very blind
animal that lives
underground
The mole
The mole is also
a measure widely
used in
chemistry
The mole
One mole is the
relative formula mass
(Mr) of a compound, or
relative atomic mass
(Ar) of an element,
expressed in grams
The mole
For example, the Ar
of carbon is 12.
The mole
For example, the Ar
of carbon is 12.
So the mass of one
mole of carbon is 12g.
The mole
For example, the Ar
of carbon is 12.
So the mass of one
mole of carbon is 12g.
How
simple is
that?
The mole
What’s the mass of
one mole of lead?
The mole
What’s the mass of
one mole of lead?
Ar of lead (Pb) = 207
So that mass of one
mole of lead is 207g
The mole
Let’s get a little more
clever now and
calculate the mass of
moles from the
relative formula mass
(Mr)
Don’t
panic!
The mole
For example, the Mr
of sodium hydroxide:
NaOH = 23 + 16 + 1
= 40
The mole
For example, the Mr
of sodium hydroxide:
NaOH = 23 + 16 + 1
= 40
So the mass of one
mole of sodium
hydroxide is 40g
The mole
What’s the mass of
one mole of calcium
carbonate?
The mole
What’s the mass of
one mole of calcium
carbonate?
Mr of CaCO3 =
40 + 12 + 48 = 100
The mole
What’s the mass of
one mole of calcium
carbonate?
Mr of CaCO3 =
40 + 12 + 48 = 100
So one mole of CaCO3
= 100g
This isn’t
rocket
science!
Important equation
Steady
as you
go!
Important equation
Number of
moles
= mass used
Mr
Steady
as you
go!
Important equation
Number of
moles
= mass used
Mr
Eg how many moles are there
in 20g of sodium hydroxide?
Steady
as you
go!
Important equation
Number of
moles
= mass used
Mr
Eg how many moles are there
in 20g of sodium hydroxide?
Number of =
moles
= 0.5
20
40
Steady
as you
go!
Important equation
Number of
moles
= mass used
Mr
Eg how many moles are there
in 20g of sodium hydroxide?
Number of =
moles
20
40
= 0.5
We could even re-arrange
the equation
Steady
as you
go!
Number of
moles
= mass used
Mr
Mass used = number of x Mr
moles
Number of
moles
= mass used
Mr
Mass used = number of x Mr
moles
Eg. What’s the mass of 2 moles of calcium carbonate?
Number of
moles
= mass used
Mr
Mass used = number of x Mr
moles
Eg. What’s the mass of 2 moles of calcium carbonate?
Mass used =
=
2
x
200g
100
The mole
Lesson 2
a) Relative
formula
mass
b) Chemical
formulae
and
Chemical
equations
1.18 write word equations and balanced
chemical equations to represent the
reactions studied
in this specification
1.19 use the state symbols (s), (l), (g) and
(aq) in chemical equations to represent
solids,
liquids, gases and aqueous solutions
respectively
1.20 understand how the formulae of simple
compounds can be obtained experimentally,
including metal oxides, water and salts
containing water of crystallisation
1.21 calculate empirical and molecular
formulae from experimental data
1.22 calculate reacting masses using
experimental data and chemical equations
1.23 carry out mole calculations using
volumes and molar concentrations.
Lesson 2
a) Relative
formula
mass
b) Chemical
formulae
and
Chemical
equations
1.18 write word equations and balanced
chemical equations to represent the
reactions studied
in this specification
1.19 use the state symbols (s), (l), (g) and
(aq) in chemical equations to represent
solids,
liquids, gases and aqueous solutions
respectively
1.20 understand how the formulae of simple
compounds can be obtained experimentally,
including metal oxides, water and salts
containing water of crystallisation
1.21 calculate empirical and molecular
formulae from experimental data
1.22 calculate reacting masses using
experimental data and chemical equations
1.23 carry out mole calculations using
volumes and molar concentrations.
Using chemical symbols
Using chemical symbols
Each element is represented by a different
symbol
…… eg Fe for iron, Na for sodium, O for oxygen
All of these symbols are in the PERIODIC TABLE
Using chemical symbols
Each element is represented by a different
symbol
…… eg Fe for iron, Na for sodium, O for oxygen
All of these symbols are in the PERIODIC TABLE
We can use these symbols to show molecules of
compounds, and they can show us the ratio of the
different elements which combine to form
compounds
Using chemical symbols
Each element is represented by a different
symbol
…… eg Fe for iron, Na for sodium, O for oxygen
All of these symbols are in the PERIODIC TABLE
We can use these symbols to show molecules of
compounds, and they can show us the ratio of the
different elements which combine to form
compounds
Eg. H2O
CO2
NH3
Using chemical symbols
Let’s recap on what
we covered earlier.
Using chemical symbols
Eg. Sodium hydroxide
NaOH
1 atom Na: 1 atom oxygen: 1 atom hydrogen
Using chemical symbols
Eg. Sodium hydroxide
NaOH
1 atom Na: 1 atom oxygen: 1 atom hydrogen
Eg. Calcium carbonate
CaCO3
1 atom Calcium, 1 atom carbon, 3 atoms oxygen
Using chemical symbols
Eg. Magnesium nitrate
Mg(NO3)2
1 atom Magnesium, 2 atoms nitrogen, 6 atoms oxygen
Using chemical symbols
Eg. Magnesium nitrate
Mg(NO3)2
1 atom Magnesium, 2 atoms nitrogen, 6 atoms oxygen
Eg. Aluminium sulphate
3Al2(SO4)3
6 atoms aluminium, 9 atoms sulphur, 36 atoms oxygen
Equations
Equations
REACTANTS
PRODUCTS
Equations
REACTANTS
Sodium
+ water
PRODUCTS
sodium + hydrogen
hydroxide
Equations
REACTANTS
Sodium
Na
PRODUCTS
+ water
sodium + hydrogen
hydroxide
+
NaOH +
H 2O
H2
Equations
REACTANTS
Sodium
PRODUCTS
+ water
sodium + hydrogen
hydroxide
Na
+
H 2O
NaOH +
H2
2Na
+
2H2O
2NaOH +
H2
Equations
REACTANTS
Sodium
PRODUCTS
+ water
sodium + hydrogen
hydroxide
Na
+
H 2O
NaOH +
H2
2Na
+
2H2O
2NaOH +
H2
2Na(s)
+
2H2O(l)
2NaOH(aq) + H2(g)
Equations
You need to know your state symbols
(s)= solid
(l) = liquid
(aq) = aqueous solution
(g) = gas
Equations
You also need to be able to:
• write word equations when required
• recall formulae of simple covalent
compounds
• write down formulae for simple ionic
compounds
• interpret chemical formulae of
molecules
• interpret symbol equations including
state symbols
Simple covalent formulae
Water H2O
Carbon dioxide CO2
Ammonia NH3
Hydrogen H2
Oxygen O2
Nitrogen N2
Sulphur dioxide SO2
Methane CH4
Simple Ionic Formulae
Sodium chloride NaCl
Calcium chloride CaCl2
Magnesium oxide MgO
Hydrochloric acid HCl
Sulphuric acid H2SO4
Nitric acid HNO3
Sodium hydroxide NaOH
Potassium hydroxide KOH
Calcium hydroxide Ca(OH)2
Calcium carbonate CaCO3
Aluminium oxide Al2O3
Iron oxide Fe2O3
Writing balanced equations
Writing balanced chemical
equations can be good /
bad for your health!
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
H2(g)
+
oxygen 
O2(g)
water
H2O
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
H2(g)
+
oxygen 
O2(g)
water
H2O
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
H2(g)
2H
+
oxygen 
O2(g)
2O
water
H2O
2H 1O
THERE MUST BE EQUAL NUMBERS OF
ATOMS OF EACH ELEMENT ON BOTH
SIDES OF THE EQUATION
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
H2(g)
2H
+
oxygen 
O2(g)
2O
water
H2O
2H 1O
x
THERE MUST BE EQUAL NUMBERS OF
ATOMS OF EACH ELEMENT ON BOTH
SIDES OF THE EQUATION
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
2H2(g)
4H
+
oxygen 
O2(g)
2O
water
2H2O
4H 2O
THERE MUST BE EQUAL NUMBERS OF
ATOMS OF EACH ELEMENT ON BOTH
SIDES OF THE EQUATION
Writing balanced equations
The basic rule (golden rule #1)
Hydrogen
2H2(g)
4H
+
oxygen 
O2(g)
2O
water
2H2O
4H 2O
THERE MUST BE EQUAL NUMBERS OF
ATOMS OF EACH ELEMENT ON BOTH
SIDES OF THE EQUATION
Writing balanced equations
FOUR important steps:
1
2
3
4
• Write a word equation for the reaction
Writing balanced equations
FOUR important steps:
1
2
3
4
• Write a word equation for the reaction
• Put in the formulae for the elements or
compounds
Writing balanced equations
FOUR important steps:
1
• Write a word equation for the reaction
2
• Put in the formulae for the elements or
compounds
3
• Balance the equation – put numbers in front of
the reactants and products where necessary
4
Writing balanced equations
FOUR important steps:
1
• Write a word equation for the reaction
2
• Put in the formulae for the elements or
compounds
3
• Balance the equation – put numbers in front of
the reactants and products where necessary
4
• Complete the balanced symbol equation
using state symbols
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1
2
3
4
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1
Mg
2
3
4
+
O2

MgO
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1
Mg
2
3
4
+
O2

MgO
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1
2
3
4
Mg
1
+
O2
2

MgO
1 1
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1

+
2
Mg
1
O2
2
+
3
2Mg
2
O2 
2
4
MgO
1 1
2MgO
2 2
Writing balanced equations
Example 1:
Magnesium + Oxygen  Magnesium oxide
1

+
2
Mg
1
O2
2
+
3
2Mg
2
O2 
2
2MgO
2 2
2Mg(s)
+
O2(g) 
2MgO(s)
4
MgO
1 1
Writing balanced equations
Example 2:
nitrogen
1
2
3
4
+ hydrogen  ammonia
Writing balanced equations
Example 2:
+ hydrogen  ammonia
nitrogen
1
2
3
4
N2
2
+
H2
2

NH3
1 3
Writing balanced equations
Example 2:
+ hydrogen  ammonia
nitrogen
1
+
2
N2
2
H2
2
+
3
N2
2
3H2
6
4


NH3
1 3
2NH3
2 6
Writing balanced equations
Example 2:
+ hydrogen  ammonia
nitrogen
1
+
2
N2
2
H2
2
+
3
N2
2
3H2
6
4
N2 (g)
2
+

NH3
1 3

3H2 (g)
6
2NH3
2 6

2NH3 (g)
2 6
End of Lesson 2
In this lesson we have covered:
Relative Formula Mass
Chemical Formulae
Chemical Equations