THE MOLE CONCEPT,

CHEMICAL FORMULA
AND
EQUATION
 ATOM
-the _____________ particle of an element that can
participate in a chemical reaction.
-Due to the mass of atom very small. So, cannot
weigh atom but, we determine the mass of one atom
RELATIVE to another which is used as a standard
• First, chemist choose hydrogen as standard for
comparing mass because it is the LIGHTEST atom
• But this method is not always convenient because:
(a) Hydrogen have 3 isotopes
(b)Not many elements react with hydrogen
• Then, the oxygen atom was chosen as standard but also posed
the same problem
• Finally, the scientists agreed to use carbon-12 as the standard.
 Carbon-12 AS THE STANDARD

Used as a reference
Easily combine with
standard in mass
other elements
spectrometer
 RELATIVE ATOMIC MASS, RAM
The average mass of an atom of the element
compared to 1/12 of the mass of one Carbon-12 atom

RAM =

P/S : Ar does not have any unit because we

compared it to standard
• The relative atomic mass
of helium is 4.
This means the average
mass of one atom of
helium is 4 times the mass
of 1/12 of carbon-12
atom.
 RELATIVE MOLECULAR MASS, RMM
The average mass of the molecule compared to
1/12 of the mass of one Carbon-12 atom

RMM =

P/S :
•Mr does not have any unit because we compared it to standard
•Concept: adding up the RAM of all atoms that are present in
the molecule
 RELATIVE FORMULA MASS, RFM
(used for ionic substances)
•The Relative Formula Mass of an ionic substance have the
_______________ like Relative Molecular Mass, RMM
•Concept: adding up the RAM of all atoms that are present
in the ionic substances
 Exercises
• Answer the question below by referring to the Periodic Table of Elements:
1. O2 2. S8 3. CuCl2
4. CH4 5. NO2 6. CH3COOH
7. Zn(OH)2 8. Cu(NO3)2 9. CuSO4.5H2O
10. H3PO4 11. HCl 12. I2
13. PCl5 14. CaCO3 15. Al(NO3)3
16. MgSO4.7H2O 17. Zn3(PO4)2 18. Al2(SO4)3
19.C5H11OH 20. CuCO3.10H2O 21. K2Cr2O7
 EXERCISES
1. The relative formula mass of a metal nitrate, X(NO3)2 is 189. Find the relative
atomic mass of the metal X.

2. The relative formula mass of hydrated Z carbonate Z2CO3.10H2O is 286.

What is the relative atomic mass of the metal Z.

3. Gypsum, CaSO4.2H2O is widely used in plastering of walls and ceilings. Show

the relative molecular mass of gypsum is 172

4. The element chlorine forms a compound with oxygen with the molecular
formula Cl2On. The relative molecular mass of compound is 183. What is the
value of n?
How do chemist measure the amount of substances?

a MOLE

An amount of substance that contains as many particles as

the number of atoms in exactly 12 g of Carbon-12

The symbol of mole is mol

 How many atoms in 12 g of Carbon-12?

The value of 1 mol of substance is

________________ particles

AVOGADRO CONSTANT, NA
-Defined as the number of particles in one mole
of a substance
 AVOGADRO CONSTANT, NA
-1 mole of substance contains
6.02 x 1023 particles

•1 mole of atomic substance = 6.02 x 1023 atoms

•1 mole of molecular substances = 6.02 x 1023 molecules
•1 mole of ionic substances = 6.02 x 1023 ions
EXAMPLES:
0.5 mol of chlorine gas, Cl2
= _____________________ molecules of chlorine
= _____________________atoms of chlorine

0.2 mol of water, H2O

= ______________________ molecules of water
= ______________________ atoms
( means: 2 mol of H atoms and 1 mol O)

Try: a) 1.25 mol of bromine, Br2

b) 2.5 mol of carbon dioxide, CO2
 Relationship between the number of moles and
the number of particles
x NA
No. of Moles No. of Particles
NA

Simplest way to remember:

 EXERCISES:
1. Calculate the number of particles in the following
substances:(NA=6.02 x 1023 mol-1)
a) 0.28 mol of copper, Cu
b) 8.5 mol of ammonia, NH3
c) 36 mol of H2O
2. Calculate the number of mole of the following substances:
(NA=6.02 x 1023 mol-1)
a) 9 x 1023 of beryllium atoms
b) 7.5 x 1024 of methane (CH4) molecules
c) 3 x 1022 of carbon dioxide molecules, CO2
 EXERCISES:
Given [Avogadro Constant = 6.02 x 1023 mol-1]

1. Calculate the number of molecules in:

a) 2 mol of chlorine gas, Cl2
b) 3.5 mol of ammonia gas, NH3
c) 0.25 mol of magnesium sulphate, MgSO4

2. Calculate the number of atoms in

a) 1.25 mol of iron, Fe
b) 3.2 mol of helium atom
c) 0.5 mol of ozone gas,O3
d) 0.75 mol of Iodine molecules, I2

3. A sample contains 6.02 x 1025 molecules of water. How many

moles of water are there in the sample?
 EXERCISES:
Given [Avogadro Constant = 6.02 x 1023 mol-1]

4. Find the number of atoms in 0.2 mol of aluminium atom.

5. Which of the following substances contains 1.204 x 1023 atoms?

a) 1 mol of nitrogen gas

b) 1 mol of ammonia

c) 1 mol of water

d) 1 mol of argon
 MOLAR MASS

The mass of 1 mole of a Relative mass (RAM or

substance RMM) of a substance

The mass of NA (6.02 x 1023 particles)

• unit of molar mass: grams per mole or g mol-1

•Molar mass is equal to the relative molecular mass
 Determining the molar mass of substances
Copper, Cu Water, H2O Sodium chloride, NaCl
• Copper consists of • Water consists of • Sodium chloride
copper atoms H2O molecules consists of NaCl
• RAM of copper = 64 • RMM of water = units
• Molar mass of 2(1) + 16 = 18 • RFM of sodium
copper = 64 g mol-1 • Molar mass of water chloride =
= 18 g mol-1 23 + 35.5 = 58.5
• Molar mass of
sodium chloride =
58.5 g mol-1
Relationship between the number of moles
and the mass of a substance

Mass
(g)

Number of Molar Mass

moles (g mol-1)
From Ar and Mr
(mol)

Mass = Number of moles x Molar mass

(g) (mol) (g mol-1)
1. Calculate the mass, in grams of
(a)0.3 mol aluminium, Al
(b)2 mol sodium sulphate, Na2SO4
2. How many moles of atoms or molecules are there in
(a)5.6 g of iron, Fe
(b)3.2 g of methane, CH4
3. Calculate the number of atoms found in 1.2 g of
magnesium, Mg
[NA = 6.02 x 1023]

4. Calculate the mass in gram for 1.5 x 1023 molecules of

chlorine, Cl2 [NA = 6.02 x 1023]
 EXERCISES
[Relative atomic mass: Mg, 24; O, 16, Cl, 35.5;
Avogradro constant: 6.02 x 1023)
1. Calculate the number of moles found in 20 g of magnesium
oxide, MgO.
2. Calculate the mass in gram found in 0.2 mol of magnesium
oxide, MgO.
3. How many magnesium ions are there in 30 g of magnesium
oxide, MgO.
4. Calculate the mass in gram of 3 x 1022 ions of magnesium
oxide, MgO.
 EXERCISES
[Relative atomic mass: Mg, 24; O, 16, Cl, 35.5;
Avogradro constant: 6.02 x 1023)
5. Calculate the number of moles found in 9.5 g of
magnesium chloride, MgCl2.
6. Calculate the mass in gram found in 0.3 mol of
magnesium chloride, MgCl2.
7. How many chloride ions are there in 19 g of magnesium
chloride, MgCl2.
8. Calculate the mass in gram of 3 x 1022 ions of magnesium
chloride, MgCl2 .
3.4 The Mole & the Volume of Gas

MOLAR VOLUME

- volume occupied by 1 mole

of any gas

22.4 dm3 at STP 24 dm3 at Room Conditions

(0°C and 1 atm) (25°C and 1 atm)
 Volume
(dm3)

Number of Molar Volume

moles (dm3 mol-1)
(mol)

Volume = Number of moles x Molar Volume

(dm3) (mol) (dm3 mol-1)
 EXERCISES
1. Calculate the volume of 0.075 mol of carbon dioxide gas
measured at STP [Molar volume: 22.4 dm3 mol-1 at STP]
2. Find the number of moles of 4800 cm³of ammonia gas at
room conditions [Molar volume: 24 dm3 mol-1 at room
condition]
3. Calculate the volume of the following gases at STP:
[Molar volume: 22.4 dm3 mol-1 at STP]
a) 0.5 mol of oxygen gas
b) 0.09 mol of carbon dioxide gas
 EXERCISES
4. Calculate the number of mole of the following gases at
room conditions
[Molar volume: 24 dm3 mol-1 at room conditions]
a) 3 dm3 of methane gas
b) 2000 cm3 of oxygen gas

5. What is the volume of 8 g of sulphur dioxide gas, SO2 at

room temperature and pressure?
[Relative atomic mass: S, 32; O, 16,
Molar volume: 24 dm3 mol-1 at room conditions]
 EXERCISES
6. The volume of ethane gas, C2H6 is 6720 cm3 at standard
temperature and pressure. What is the mass of ethane gas?
[Relative atomic mass: C, 12; H, 1. Molar volume: 22.4 dm3 mol-1 at
STP]

7. How many molecules present in 1.2 dm3 of oxygen gas, O2 at room

conditions.[Relative atomic mass: O, 16. Molar volume: 24 dm3 mol-1
at room conditions. Avogadro constant: 6.02 x 1023]

8. Calculate the volume of the ammonia, NH3 gas at standard

temperature and pressure when there are 7.5 x 1022 molecules are in
it.[Molar volume: 22.4 dm3 mol-1 at STP. Avogadro constant: 6.02 x
1023]
 Chemical
Formula
Representation of a chemical substance using alphabets to
represent the atoms and subscript numbers to show the
numbers of each type of atoms found in the elementary entities
of the substance.

Copper (II)
Sulphate, CuSO4
 Chemical formula
tell us about:

All the elements Calculate Ar or

present in the Mr of the
compound compound
Number of
atoms of each
element
 Types of Chemical
Formula

Empirical formula Molecular formula

- Determine based on
observation or experiment
(not from theory)
 Formula that shows the
Empirical simplest ratio of the number
Formula of atoms of each element in
a compound
Element X Y
Mass (g)
No. of moles (mol)
Mole ratio
Simplest mole ratio of atoms
Empirical formula
Examples 1:
60 g of aluminium sulphide contains 38.4 g of
sulphur. Find the empirical formula of the
compound.
[Relative atomic mass: Al =27; S =32 ]

Answer:
Al2S3
 Examples 2:
Find the empirical formula of a compound that
consists of 32.4% of sodium, 22.6% of sulphur
and 45% of oxygen.
[Relative atomic mass: Na =23; S =32; O =16 ]

Answer:
Na2SO4
 Examples 3:
11 g oxide M reduced to form 6.2 g metal M.
Empirical formula of oxide M is ?
[Relative atomic mass:M = 31 ; O = 16]

Answer:
M2O3
 Examples 4:
In an experiment, 24 g of element X reacts
with 32 g sulphur to form a compound. What
is the empirical formula of that compound?
[Relative atomic mass: X = 6; S = 32 ]

Answer:
X4 S
 Examples 5:
6.24 g of element X combines with 1.28 g of
oxygen to produce a compound with an
empirical formula X2O. What is the relative
atomic mass of X?
[Relative atomic mass: O,16 ]
Answer:
Ar of X = 39
 Examples 6:
10 g of metal oxide with a formula of MO can
be completely reduced to 8 g of metal M.
What is the relative atomic mass of M?
[Relative atomic mass: O,16 ]

Answer:
Ar of M = 64
 EXERCISES
1. 0.20 g of calcium reacts with fluorine to give 0.39 g of calcium
fluoride. Find the empirical formula of the fluoride compound.
[Relative atomic mass: Ca=40; F=19]
2. A solvent for nail varnish is found to contain 62% carbon, 10.34%
hydrogen and the rest is oxygen. Determine the empirical
formula of the solvent.
[Relative atomic mass: C=12; H= 1; O =16]
 EXERCISES
3. 11.2 g of metal M combined with 21.3 g of chlorine to form
a compound with the empirical formula of MCl3.
Determine the relative atomic mass of M.
[Relative atomic mass: Cl= 35.5]
4. When 11.95 g of metal X oxide is reduced by hydrogen,
10.35 g of metal X is produced. Find the empirical formula of
metal X oxide.
[Relative atomic mass: X =207; O =16]
 EXERCISES
5. Ethanoic acid is an important ingredient of vinegar. The
empirical formula of this acid is (CH2O). Given that its molar
mass is 60 gmol-1. Find its molecular formula.
[Relative atomic mass: C =12; H =1; O =16]
6. Find the percentage composition by mass of nitrogen in the
(NH4)2SO4.
7. Butane has the empirical formula of C2H5 and relative
molecular mass of 58. Find its molecular formula
[Relative atomic mass: C= 12; H =1]
 Formula that shows the actual
Molecular
number of atoms of each element
Formula
found in a molecule of a compound
(means: Molecular Formula is
multiples of its empirical formula)

Molecular
= ( Empirical Formula )n
Formula

P/S: n – positive integer

 EXAMPLES:
Compound Empirical n Molecular formula
formula

Water H2O 1
Ammonia NH3 1
Ethane CH3 2

Benzene CH 6

Glucose CH2O 6
 EXAMPLES:
Compound Empirical n Molecular formula
formula

Water H2O 1 H2O

Ammonia NH3 1 NH3
Ethane CH3 2 (CH3)2=C2H6
Benzene CH 6 (CH)6=C6H6

Glucose CH2O 6 (CH2O)6 =C6H12O6

Examples 1:
Butane has the empirical formula of C2H5 and
relative molecular mass of 58. Find its molecular
formula.
[Relative atomic mass: C =12; H =1]

Answer:
C4H10
 Examples 2:
Determine the percentage composition by mass of
water in hydrated copper (II) sulphate, CuSO4.5H2O
[Relative atomic mass: Cu =64; S =32; O =16; H =1]

Answer:
36%
 Evaluation 1:
Tobacco contains nicotine. Chemical analysis of the
compound shows that nicotine contains 74.1% carbon,
8.64% hydrogen and the rest is nitrogen.
[Relative atomic mass: C= 12; H= 1; N =14 ]

(a) Determine the empirical formula of nicotine

(b) If the relative molecular mass of nicotine is 162, what is its
molecular formula?
 Evaluation 2:
Hydrocarbon X has a composition of carbon 85.71%
and hydrogen 14.29%.
[Relative atomic mass: C =12; H =1 ]

(a) Determine the empirical formula of the compound

(b) If the relative molecular mass of X is 56, what is its
molecular formula?
 Evaluation 3:
0.18 g of element P combines with 0.16 g of
element Q to form a compound with its
empirical formula P2Q3. What is the relative
atomic mass of the element P?
[Relative atomic mass: Q= 16 ]
 Evaluation 4:
An insecticide contains 25.3% carbon and 74.7%
chlorine.
[Relative atomic mass: C =12; Cl = 35.5 ]

(a) Determine the empirical formula of the compound

(b) If the relative molecular mass of the insecticide is
285, what is its molecular formula?
 IMPORTANT EXPERIMENTS
1. To determine the empirical formula of copper(II) oxide,
CuO
Product:
Copper(II) oxide → Copper
(black) (brown)

2. To determine the empirical formula of magnesium

oxide, MgO
Product:
Magnesium + oxygen → Magnesium oxide
 To determine the empirical formula of Copper(II) oxide, CuO

Materials:

Water, copper(II) oxide powder, zinc

granules, 1.0 mol dm -3 hydrochloric
acid, wooden splinter and cotton buds

Apparatus:

Boiling tube, rubber stoppers, rubber

tube, 12 cm glass tube, 10 cm glass
tube, spirit lamp, retort stand with
clamp, wooden block, electronic
balance and spatula
 To determine the empirical formula of Copper(II) oxide, CuO
Procedure:
1. Weigh the mass of 12 cm glass tube using an electronic balance
and record its mass.
2. Put some copper(II) oxide powder into the glass tube. Use the
wooden splinter to move copper(II) oxide powder to the middle
of the glass tube. Weigh the mass of the glass tube together with
its contents and record the mass.
3. Fill 2/3 of the boiling tube with water.
4. Close the boiling tube with a rubber stopper that has a 12 cm
glass tube. Clamp the boiling tube onto the retort stand
5. Insert a few zinc granules into another boiling tube. Add 1.0 mol
dm-3 hydrochloric acid into the boiling tube until it is 1/3 full.
6. Close the boiling tube with a rubber stopper that has a 10 cm
glass tube. Clamp the boiling tube onto the other retort stand.
7. Connect the glass tube that contains copper(II) oxide powder as
diagram
 To determine the empirical formula of Copper(II) oxide, CuO
Procedure:
8. Let the hydrogen gas flow for 10 seconds by allowing
the air bubbles to be released in the water before
starting the heating process.
9. Heat copper(II) oxide using a spirit lamp with a
continuous flow of hydrogen gas through the glass
tube.
10. Stop the heating when the black colour of copper(II)
oxide turns brown completely.
11. Keep a continuous flow of hydrogen gas until the glass
tube is cooled back to room temperature.
***If necessary, hold the spirit lamp by moving it under the
glass tube to heat the remaining powder that is still black so
that all black powder turns brown.
 To determine the empirical formula of Copper(II) oxide, CuO
Procedure:
12. Remove the glass tube that contains brown powder.
Eliminate water drops at the end of the glass tube with
a cotton bud.
13. Weigh the mass of the glass tube together with its
contents and record its mass.
14. Repeat the heating, cooling and weighing processes
from steps 9 to 13 until a constant mass reading is
obtained
15. Record the constant mass in Table:
 To determine the empirical formula of Copper(II) oxide, CuO

Description Mass (g)

Glass tube
Glass tube + copper(II) oxide
Glass tube + copper
copper
oxygen
To determine the empirical formula of copper(II) oxide, CuO
Precaution steps must be taken:
BEFORE:
What is the purpose of using zinc
granules and hydrochloric acid in this
experiment?

- to produce hydrogen gas

To determine the empirical formula of copper(II) oxide, CuO
Precaution steps must be taken:
BEFORE:
Let the hydrogen gas flow for 10
seconds by allowing the air bubbles to
be released in the water before starting
the heating process.
Why???
- to remove all the air because mixture of
H2 and air can cause explosion when
lighted
To determine the empirical formula of copper(II) oxide, CuO
Precaution steps must be taken:
DURING:
Heat copper(II) oxide using a spirit lamp
with a continuous flow of hydrogen gas
through the glass tube.
Why???

-to ensure air does not enter glass

tube (can cause explosion)
To determine the empirical formula of copper(II) oxide, CuO
Precaution steps must be taken:
DURING:
Keep a continuous flow of hydrogen gas
until the glass tube is cooled back to
room temperature.
Why???

- to prevent hot copper produced react

with oxygen in the air to form copper(II)
oxide again
To determine the empirical formula of copper(II) oxide, CuO
Precaution steps must be taken:
AFTER:
Repeat the heating, cooling and
weighing process until constant mass
reading is obtained
Why???

- to ensure that all copper(II) oxide has

changed into copper
 To determine the empirical formula of
magnesium oxide, MgO

Materials:
10 cm magnesium ribbon and
sand paper
Apparatus:
Crucible with lid, tongs, Bunsen
burner, tripod stand, pipeclay
triangle and electronic balance
 To determine the empirical formula of
magnesium oxide, MgO
Procedure:
1. Weigh and record the mass of a crucible
together with its lid
2. Rub 10 cm magnesium ribbon with a sand
paper until shiny. Coil the magnesium ribbon
and put it in the crucible
3. Weigh and record the mass of the crucible
together with its lid and the coil of
magnesium ribbon
4. Set up the apparatus as shown in Diagram
5. First, heat the crucible without its lid.
6. When magnesium ribbon starts to burn, close
the crucible with its lid.
 To determine the empirical formula of
magnesium oxide, MgO
Procedure:
7. Using a pair of tongs, lift the lid slightly from
time to time and quickly place it back
8. When the burning of magnesium ribbon is
complete, take off the lid and heat the
crucible with high temperature for 1 to 2
minutes.
9. Put back the lid of the crucible and allow it to
cool to room temperature.
10.Weigh the mass of crucible together with its
lid and its contents again.
11.Repeat the heating, cooling and weighing
process until a constant mass is obtained
12.Record the constant mass in Table.
To determine the empirical formula of Copper(II) oxide, CuO

Description Mass (g)

Crucible + lid
Crucible + lid + magnesium ribbon
Crucible + lid + magnesium oxide
Magnesium
oxygen
To determine the empirical formula of
magnesium oxide, MgO
• Important steps:
The magnesium ribbon is
cleaned with sandpaper
before it was heated
Why???

- To remove the oxide layer

on its surface
To determine the empirical formula of
magnesium oxide, MgO
• Important steps:
During heating, the lid of the
crucible is lifted at intervals.
Why???

- to allow the oxygen from the

air to enter for complete
combustion of magnesium
To determine the empirical formula of
magnesium oxide, MgO
• Important steps:
The lid of the crucible is closed
immediately as soon as the
magnesium started burning
Why???

- To prevent white fumes

(magnesium oxide) formed
from escaped to air
To determine the empirical formula of
magnesium oxide, MgO

• Important steps:
The heating, cooling and
weighing process is
repeated until a constant
mass is obtained
Why???

- To ensure complete
combustion of the magnesium
Chemical Formulae of Ionic Compounds
IONS

Particles with charges

Y+ Xˉ

Positively charged Negatively charged

ions called ions called ANIONS
CATIONS
Formed from non-
Formed from metal metal atom
atom
 Formulae of common cations and anions

Cation Formula of cation Anion Formula of anion

Sodium ion Na+ Oxide ion O2-
Potassium ion K+ Chloride ion Cl-
Aluminium ion Al3+ Bromide ion Br-
Zinc ion Zn2+ Iodide ion I-
Magnesium ion Mg2+ Hydroxide ion OH-
Iron(II) ion Fe2+ Carbonate ion CO32-
Iron(III) ion Fe3+ Nitrate ion NO3-
Copper(II) ion Cu2+ Sulphate ion SO42-
Calcium ion Ca2+ Phosphate ion PO43-
Silver ion Ag+ Manganate(VII) ion MnO4-
Lead(II) ion Pb2+ Thiosulphate ion S2O32-
Ammonium ion NH4+ Dichromate(VI) ion Cr2O72-
Ionic Formulae
IONIC
COMPOUND

Made up of
CATION & ANION
EXAMPLES:
Compound Cation Anion
Zinc bromide
Potassium oxide
Ionic Formulae

Constructing ionic formula of an ionic compound

Example: Potassium chloride, sodium bromide

1. Determine ions involved.

2. Determine charge of ions

3. Number of ions without the

charges
4. Write the ionic formula
Naming Chemical Compounds

REMEMBER:
1.If cation and anion have SAME VALUE of charges,
we determined it to the simplest ratio of ions eg:
Magnesium oxide
2.If the ions made up more than 1 element, we
used bracket ( ) to show the number of these
ions eg: Magnesium hydroxide, Aluminium
carbonate
Ionic Formulae
Construct the ionic formula for these compounds:
• Magnesium chloride
• Sodium sulphate
• Calcium hydroxide
• Aluminium nitrate
• Potassium phosphate
• Ammonium sulphate
•Calcium carbonate
•Copper(II) oxide
•Lead(II) sulphate
•Iron(III) hydroxide
Naming Chemical Compounds

For ionic compounds:

RULE 1

i. Name the cation.

ii. Name the anion.

EXAMPLE:
+
Na Sodium ion

Sodium
chloride
-
Cl Chloride ion
Naming Chemical Compounds

RULE 2 The use of Roman numerals

For certain metals that can form more than

one type of ions

Metal Ions
Copper, Cu + 2+
Cu Cu
Iron, Fe 2+ 3+
Fe Fe
Manganese, 2+ 4+
Mn Mn
Mn

EXAMPLE: Copper(II) oxide Copper(I) oxide

Naming Chemical Compounds

For simple molecular compounds:

RULE 3

i. Maintain the name of the 1st element

ii. Name of the 2nd element is added with ‘ide’

EXAMPLE:

+
H Hydrogen ion
Hydrogen
chloride
-
Cl Chloride ion
 The used of Greek prefixes
RULE 4
To show the number of atoms of each
elements in a compound.
EXAMPLES:
Chemical Naming
formula
NO Nitrogen monoxide
CO2 Carbon dioxide
SO3 Sulphur trioxide
CCl4 Carbon tetrachloride
PCl5 Phosphorus pentachloride
Name the following formulae:
• NaBr
• LiCl
• ZnSO4
• SO2
• Ca(OH)2
• AlPO4
• Ba(NO3)2
•(NH4)CO3
 QUIZ
• Construct a chemical formula for each of the following ionic
compounds
1. Copper(II) chloride 11. Sulphuric acid
2. Calcium carbonate 12. Barium sulphate
3. Ammonium phosphate 13. Hydrochloric acid
4. Nitric acid
5. Iron(II) hydroxide
6. Potassium manganate (VII)
7. Silver nitrate
8. Lead(II) bromide
9. Potassium dichromate(VI)
10. Aluminium oxide
 CHEMICAL EQUATIONS
-shorthand description of a chemical
reaction

Equation in WORDS Equation in SYMBOLS

-using names of -reactants and products
reactants and products are represented by
chemical formulae
 Chemical equation using symbol
tells us:

Qualitative aspect Quantitative aspect

• Reactants (starting substances) • Coefficient / the exact
proportions of reactants
• Products (new substances form)
and products in chemical
• State of reactants and products reaction
• Coefficient refers to:
Number of moles OR
number of molecules
 Symbol of equations:
Symbol Meaning Symbol Meaning
+ Separating 2 (g) Gaseous state
reactant/product

→ Produces (aq) Aqueous state

Reversible ↑ Gas released

reaction

(s) Solid state ↓ Precipitation

(l) Liquid state ∆ Heating/ Heat

energy is given
Determine the qualitative and quantitative
aspect for these chemical equations

1. 2H2(g) + O2(g) 2H2O(l)

2. CuO(s) + 2HCl(aq) CuCl2(aq) + H2O(l)

3. 2Al(s) + Fe2O3(aq) Al2O3(aq) + 2Fe(s)

 Chemical equation must be balanced
Means:

Number of atoms in = number of atoms in

reactants (left-side) products (right-side)
 Write chemical equation of:

1. Carbon monoxide gas + oxygen gas carbon dioxide

2. Magnesium reacts with oxygen gas to form magnesium oxide

3. Iron + sulphuric acid iron(III) sulphate solution +

hydrogen gas
Complete the chemical equations:
(a) Na + Cl2 → NaCl
(b) Mg + HNO3 → Mg(NO3)2 + H2
(c) C2H4 + O2 → CO2 + H2O
(d) Cu + AgNO3 → Cu(NO3)2 + Ag
(e) Pb(NO3)2 → PbO + NO2 + O2
(f) Ca + H2O → Ca(OH)2 + H2
(g) CuO + CH4 → Cu + CO2 + H2O
(h) C2H6 + O2 → CO2 + H2O
(i) MnO2 + HCl → MnCl2 + Cl2(g) + H2O
ANSWER: Complete the chemical equations:
(a) 2Na + Cl2 → 2NaCl
(b) Mg + 2HNO3 → Mg(NO3)2 + H2
(c) C2H4 + 3O2 → 2CO2 + 2H2O
(d) Cu + 2AgNO3 → Cu(NO3)2 + 2Ag
(e) 2Pb(NO3)2 → 2PbO + 4NO2 + O2
(f) Ca + 2H2O → Ca(OH)2 + H2
(g) 4CuO + CH4 → 4Cu + CO2 + 2H2O
(h) C2H6 + 7/2O2 → 2CO2 + 3H2O
(i) MnO2 + 4HCl → MnCl2 + Cl2(g) + 2H2O
Write a balanced chemical equation
(a) Magnesium metal reacts with the chlorine gas to form solid magnesium
chloride
(b) Solid calcium carbonate reacts with hydrochloric acid to form calcium
chloride aqueous, water and carbon dioxide gas
(c) When solid zinc carbonate is heated, it decomposes into zinc oxide powder
and carbon dioxide gas
(d) Potassium metal reacts with water to form potassium hydroxide and release
hydrogen gas
(e) Silver nitrate solution is added to calcium chloride solution. Silver chloride
precipitate and calcium nitrate solution are produced.
Write a balanced chemical equation:
(f) Dilute sulphuric acid reacts with sodium hydroxide solution to form
sodium sulphate solution and water
(g) Copper solid burns in oxygen gas to produce black powder of
copper(II) oxide
(h) Reaction between sulphur dioxide and oxygen to form sulphur
trioxide
(i) Neutralization reaction between sodium hydroxide and sulphuric acid
to form sodium sulphate and water
ANSWER: Write a balanced chemical equation
(a)Magnesium metal reacts with the chlorine gas to form solid magnesium
chloride
2Mg + Cl2 → 2MgCl
(b) Solid calcium carbonate reacts with hydrochloric acid to form calcium
chloride aqueous, water and carbon dioxide gas
CaCO3 + 2HCl → CaCl2 + H2O + CO2
(c) When solid zinc carbonate is heated, it decomposes into zinc oxide
powder and carbon dioxide gas
ZnCO3 → ZnO + CO2
ANSWER: Write a balanced chemical equation
(d) Potassium metal reacts with water to form potassium hydroxide and
release hydrogen gas
2K + 2H2O → 2KOH + H2
(e) Silver nitrate solution is added to calcium chloride solution. Silver
chloride precipitate and calcium nitrate solution are produced.
2AgNO3 + CaCl2 → 2AgCl + Ca(NO3)2
(f) Dilute sulphuric acid reacts with sodium hydroxide solution to form
sodium sulphate solution and water
H2SO4 + 2NaOH → Na2SO4 + 2H2O
ANSWER: Write a balanced chemical equation:
(g) Copper solid burns in oxygen gas to produce black powder of
copper(II) oxide
2Cu + O2 → 2CuO
(h)Reaction between sulphur dioxide and oxygen to form sulphur
trioxide
2SO2 + O2 → 2SO3
(i)Neutralization reaction between sodium hydroxide and sulphuric acid
to form sodium sulphate and water
2NaOH + H2SO4 → Na2SO4 + 2H2O
 Solve numerical problems
Copper(II) oxide, CuO reacts with aluminium according to
the following equation:
3CuO(s) + 2Al(s) Al2O3(s) + 3Cu(s)
Calculate the mass of aluminium required to react completely
with 12 g of copper(II) oxide, CuO
[Relative atomic mass: O,16; Al,27; Cu,64]
 Solve numerical problems
Hydrogen peroxide, H2O2 decomposes according to
the following equation:
2H2O2(l) 2H2O(l) + O2(g)
Calculate the volume of oxygen gas, O2 measured
at STP that can be obtained from the decomposition
of 34 g of hydrogen peroxide, H2O2
[Relative atomic mass: O,16; H,1, Molar volume:
22.4 dm3 mol-1 at STP]
 Evaluation 1:
Zinc metal reacts with excess hydrochloric acid to
produce zinc chloride and hydrogen gas.
[Relative atomic mass: Zn, 65;H, 1: Cl, 35.5; molar
volume at room condition = 24 dm3]
a) Write a balanced chemical equation for the reaction
b) If 2.6 g of zinc metal is used in the reaction, calculate
(i) the maximum mass of zinc chloride that can be formed
(ii) The volume of hydrogen gas that is produced at room
conditions
 Evaluation 2:
16 g of copper(II) oxide, CuO is reacted with excess
methane, CH4. Using the equation below, find the mass
of copper that is produced.

4CuO(s)+ CH4(s) 4Cu(s) +CO2(g) + 2H2O(l)

[Relative atomic mass: O,16; H,1; C,12 ; Cu,64]

Solve the questions below.
1. 2Mg(s) + O2(g) → 2MgO(s)
What is the mass of the magnesium oxide if 0.6 g of
magnesium is burnt in excess oxygen?
[RAM: O,16; Mg, 24]
2. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
What is the volume of carbon dioxide released when 5 g of
calcium carbonate reacts with hydrochloric acid at room
condition?
[RAM: C, 12; O,16; Ca, 40, molar volume: 24 dm3 mol-1 at
room condition]
3. 5.0 g of hydrated copper(II) sulphate, CuSO4.5H2O, is
heated to remove its water vapour.
CuSO4.5H2O(s) → CuSO4(s) + 5H2O(l)
Calculate the mass of water vapour removed
[RAM: H,1; O,16; S, 32; Cu,64]
4. 3.1 g of sodium oxide is formed when the sodium metal is
burnt completely in oxygen at STP.
4Na(s) + O2(g) → 2Na2O(s)
Calculate the volume of oxygen used.
[RAM: O,16; Na, 23; Molar volume: 22.4 dm3 mol-1 at STP]