1. Topic 1.3 - Formulae, equations and amounts of substance
Lesson 1 - The basics
a. demonstrate an understanding of the terms atom, element, ion, molecule, compound, empirical and molecular formulae
b. write balanced equations (full and ionic) for simple reactions, including the use of state symbols
c. demonstrate an understanding of the terms relative atomic mass, amount of substance, molar mass and parts per million (ppm), eg gases in the atmosphere, exhausts, water pollution
Connector:
Define an atom, a compound and an ion.
Draw a lithium atom ( At. No. 3; At. Mass 7)
List the THREE main sub-atomic particles, and give their relative masses and electrical charges.
Crowe 2011

2. An atom is the smallest, electrically neutral, particle of an element that can take part in a chemical change.
A molecule is the smallest, electrically neutral, particle of an element or compound that can exist on its own.
An ion is an atom, or group of atoms, which carries an electric charge.

3. Lithium Atom
 A Lithium has 3 protons and 4 neutrons inside the nucleus with 3 electrons orbiting around the nucleus.

5. Write the word equation and then the balanced equation, including state symbols for the following reactions:
Hydrogen and oxygen combining to form water.
Calcium carbonate decomposing into calcium oxide and carbon dioxide.
Hydrochloric acid reacting with magnesium to produce hydrogen gas and a solution of magnesium chloride.
Sulphuric acid being neutralised by sodium hydroxide to give a solution of sodium sulphate.
Zinc oxide reacting with sulphuric acid to give a solution of zinc sulphate.
Aluminium combining with oxygen to form its oxide.
Methane under going complete combustion.

6. Relative atomic mass & molar mass
Explain these terms.
RAMS & MOLES

7. Relative atomic mass The definition of Relative Atomic Mass (Ar):
The mass of a single atom on a scale on which the mass of an atom of carbon—12 has a mass of 12 atomic mass units.
The relative atomic mass does not have units.
12 hydrogen atoms have the same mass as 1 carbon atom

8. Relative Atomic Mass of elements
The atoms of each element have a different mass.
Carbon is given a relative atomic mass (RAM) of 12.
The RAM of other atoms compares them with carbon.
Eg. Hydrogen has a mass of only one twelfth that of carbon and so has a RAM of 1.
Below are the RAMs of some other elements.
Element
Symbol
Times as heavy as carbon
R.A.M
Helium He
one third
Beryllium Be
three quarters
Molybdenum Mo
Eight
Krypton Kr
Seven
Oxygen O
One and one third
Silver Ag
Nine
Calcium Ca
Three and one third 4 9 96 84 16
108 40

9. Molar mass or Moles
The mole is the formula mass in g’s of an atom, molecule, or compound.
Example: Water
H2O = (2xH)+(O) = (2x1)+16 = 18
So water has a molar mass of 18g or
1 mole of water weighs 18g

10. Molar mass if the formula mass in g
Calculate the formula mass of the compounds below.
(N=14; H=1; Na=23; O=16; Mg=24; Ca=40)
Substance
Formula
Formula Mass
Ammonia
NH3
Sodium oxide
Na2O
Magnesium hydroxide
Mg(OH)2
Calcium nitrate
Ca(NO3)2
14 + (3x1)=17
(2x23) + 16 =62
24+ 2(16+1)=58
40+ 2(14+(3x16))=164
What is the relationship between molar mass and formula mass?
Molar mass if the formula mass in g

11. Calculating Moles
The number of moles present in a weighed sample can be calculated using this equation:
Similarly
mass = moles x R.A.M.
Number of moles = mass
R.A.M.
How many moles are there in
4.4g of carbon dioxide?
80g of methane?
14.2g of chlorine?
128g of sulphur?
1kg of calcium carbonate?
What is the mass of
3 moles of hydrogen gas?
0.5 mole of copper(II) oxide?
4 moles of sodium chloride?
0.3 mole of ethene?
0.25 mole helium?

12. Percentage Composition
% Z = (Number of atoms of Z) x (atomic Mass of Z) Formula Mass of the compound
Calculate the percentage of oxygen in carbon dioxide
CO2
12 +(2x16)=44
2 x 16 / 44 = 72.7%

13. parts per million (ppm)
This is a way of expressing very dilute concentrations of substances e.g gases in the atmosphere or in exhaust fumes, pollutants in a river, etc.
Just as per cent means out of a hundred, so
parts per million, or ppm, means out of a million.
Convert 0.025% into ppm
= ? x = ? = 250ppm
Convert 0.19g/litre into ppm
= ? x = ? = 190ppm

14. Past paper questions
In 2006, the concentration of carbon dioxide in the atmosphere was 382 ppm. This is equivalent to
= x
A halogenoalkane, bromomethane, CH3Br, is a toxic gas used to protect plants against insects. Health and Safety advice states that concentrations above 5 parts per million (ppm) by volume of this gas are harmful.
A research laboratory contains 2.5 × 105 dm3 of air.
Calculate the maximum volume of bromomethane, in dm3, allowed in the laboratory to comply with the advice given Jan 09

15. Exercise 1: Calculation of the Molar Mass of compounds MFE Booklet pp 6-8