Second Term Lesson Note for Week One
Class : SSS One
Subject : Chemistry
Topic : The Mole Concept
Duration : 80 Minutes
Period : Double Period
Reference Book :
Lagos State Unified schemes of work for Senior Secondary SCHOOLS, (SSS 1 – 3).
Chemistry for Senior Secondary Schools,
Online Resources
Instructional Material : Chart showing the relationship of the moles with avogadro’s number, molar mass and molar volume.
Learning Objectives : By the end of the lesson learners will be able to :
i. Define Matter, and explain the mole concept.
ii. Explains the formula mass, RAM, RMM, Avogadro’s number
iii. Calculate the Relative molecular mass of some compounds.
iv. Solve problems on mole concept with several examples.
Content :
INTRODUCTION TO MOLE CONCEPT
Matter is defined as anything that has mass and occupies space it is made up of discrete of tiny particles such as atoms, molecules and ions.
Atom : This is the smallest particle of an element which can participate/take part in a chemical reaction. E.g., O, N, F, S, Cl, Na, He etc.
NOTE: Atoms cannot exist separately.
Molecule : This is the smallest particle of a substance that is capable of independent existence and still retains the chemical properties of that substance. Examples H2, 02, F2, S8, Cl2, H2O, NaCl etc.
NOTE : A molecule is formed when two or more atoms are chemically joined together. The combination of atoms of the same type produces molecules of an element while the combination of different types of atoms produce molecule of a compound. The molecule does not lose its identity.
ATOMICITY : This is the number of atoms in a molecule of an element, most gaseous elements are diatomic. Examples comprise of noble gases and metals respectively. Example He, ,Ar, Ne, Ca, Mg, etc. P4 tetra-atomic element, O3 tri-atomic element and S8 polyatomic element.
IONS: These are atoms or group of atoms which possesses an electric charge.
There are two types of ions namely:
i. Cations which results from the loss of electrons by the atom of a metal to become positively charge. Example, K+, Na+, Ca2+, Al3+, Cr3+, Ag+, Pb2+, NH4+
ii. Anions which results from the gain of electrons by the atom of non metal to become negatively charge. Example O -2, Cl-, F -, S-2, N-3, OH –, SO42-, Cr2O72-, MnO4– etc.
RELATIVE FORMULAE MASS
The relative formulae mass of a substance can be defined as the number of times the mass of one
Formulae unit of the substance is heavier than one twelfth of the mass of one atom of carbon 12
i.e.
RELATIVE FORMULAE MASS
Mass of 1 formulae unit of a substance 1/12 x mass of atom of Carbon -12.
RELATIVE ATOMIC MASS (RAM)
The relative atomic mass (RAM) of an element is the mass of one atom of the element. R.A.M
not a whole number because of the existence of the phenomenon of isotopy.
NOTE: R.A.M has no unit.
DEFINITION:
The relative atomic mass of an element can be defined as the number of times the average mass of atom of the element is heavier than one twelfth of the mass of one atom of carbon-12.
R.A.M.=mass of I atom of the element
1/12 x mass of I atom of carbon
NOTE:
a. Carbon is used as a standard
b. The instrument used for measuring relative atomic mass is called mass spectrometer
RELATIVE MOLECULAR MASS (Mr/Rmm) of a substance is the mass of one molecule of the substance. The r.m.m. is the sum of the R.A.M. of all the atoms present in the molecule.
NOTE: The r.m.m has no unit.
DEFINITION
The relative molecule mass of an element or a compound is the number of time the mass of one
Molecule of the element or compound is heavier than one twelfth of the mass of one atom of
Carbon-12.
R.m.m. = Mass of 1molecule of substance
1/12 x mass of atom of carbon -12
= mass of 1 molecule of substance x 12
Mass o atom of carbon -12
Example
1. Calculate the relative molecular masses of each of the following
a) H2S04
b) Al2 (S04) 3
c) Fe S04 7H20
(H=1, S=32, 0=16, Al=27, Fe = 56)
SOLUTION
= 2 H + 1S + 40
= 2 x 1 + 32 + 4 x 16
2 + 32 + 64 = 98
b. Al2 (S04)3
= 2Al + 3S + 12 0
= (2×27) + (3×32) + (12×16)
= 54 + 96 + 192
= 342
c. FeS04. 7H20
= Fe+ S+40 + 7 (2H+0)
= 56 + 32 + (4×16) + (7×18)
= 56 + 32 + 64 + 126
= 278
MOLE
The mole can be defined as the amount of substance which contains Avogadro’s number of particles. The particles may be of different kinds, which may be atoms, molecules, ions, electrons, protons neutrons etc. Hence it is very necessary to state the type of particle involved.
NOTE:
. Mole is a unit of measurement
. The Avogadro’s number is constant and the value is 6.02 x1023 atoms or molecules or ions or electrons or protons or neutrons etc.
. For a reaction to occur, the particles of reactants must come together to form certain number of particles of product.
. Very large numbers of particles are to be worked with; hence it is difficult to measure individual particles in the reaction. To this effect, a unit for measuring the amount of particles in a given mass of a substance is designed and this is called a MOLE.
. From experimental work, it was found that 1 mole of substance = 6.02 x 1023 particles. This number is called AVOGADRO’S NUMBER.
. Therefore, a mole of any substance is the amount of that substance that contains the Avogadro’s number. Example just as 1 dozen of egg = 12 eggs so is 1 mole of oxygen
atoms contain 6.02 x 1023 oxygen atoms.
. 302 moles of oxygen molecules or 6 moles of oxygen atoms.
. 3MgS04 = 3 moles of MgS04 molecules or 3 moles of magnesium atom, 3 moles of sulphur atoms and 12 mole of oxygen atoms.
. 2H2 + 02 2H20 2moles of hydrogen molecules reacts with 1 mole of oxygen molecule to produce 2 moles of water.
MOLAR MASS
The mass of one mole of any substance expressed in grams unit = g/mol
Examples:
Chlorine gas (Cl2)
= 35.5 x 2, = 71g /mole
Carbon dioxide gas (C02)
= 12 + (16 x 2) = 44g/mol
THE MOLE CONCEPT
The mole can be expressed in the following ways:
i. The mole in terms of formula
ii. The mole in term of relative molecular man (R.A.M)
iii. The mole in terms of Avogadro’s number
The mole in term of the molar volume
NOTE: The expression of the mole in different ways mentioned above is known as the MOLE CONCEPT.
A. MOLE IN TERMS OF THE FORMULA
The mole can be expressed as:
Element: Mole = mass of the element
Relative Atomic Mass of Element
OR
Compound: = Mole mass in grams
Or molecule R.M.M
Example:
Calculate the number of moles of atoms, present in 40g of calcium carbonate or calciumtrioxo
Carbonate (IV) (CaC03)
Solution:
Mass of CaC03 = 40g
R.M.M. CaC03 = (40 + 12 +16)
= 100glmol
Mole (n) = Mass is g
R.M.M CaC03
N = 40g
100g/mole
= 0.4 mole
Presentation Steps :
Step 1 : The teacher revises the previous term’s work with the learners.
Step 2 : Introduces the new topic by defining the Mole Concept.
Step 3 : Describes the following Mole, atom, ions, molecule
Step 4 : Explains Mole in Terms of molar mass, avogadro’s number, molar volumes.
Step 5 : Solve several examples involving the Mole Concept.
Evaluation :
1. Calculate the R.m.m. of the following compounds
i. Calcium hydroxide Ca (OH) 2
ii. Lead (ii) trioxonitrate Pb (N03)2
iii. Ammoniumtrioxocarbonate (IV) (NH4)2C03
iv. Iron (IV) tetraoxo sulphate (VI) Fe2 (S04)3
v. FeS04.Al2 (S04)3.12H20
(R.a.m = Ca=40, 0=16, H=1,Pb = 207, N=14, C=12, Al=27, S=32, Fe =56)
2.A molecule is the smallest particle of
(A) a matter that can exist in Free State
(B) an element that can exist in Free State
(C) a radical that can exist in Free State
(D) a lattice that can exist in Free State
3. 3NH3 is
(A) three moles of ammonium
(B) three moles of ammonia
(C) six moles of ammonia
(D) six moles of ammonium
4. How many moles of substance are present is
a. 35g of oxygen gas (02)
b. 140g of sodium chloride (NaCl)
c. 150g of carbon dioxide gas (C02)
(0 – 16, Na = 23, C1 = 35.5, C =12)
Conclusion : At the end of the lesson learners were able to answer the questions correctly
Assignment :
1. Calculate the grams molecular mass for the following compounds
(a) Na2C03 (b) H3 P04
(c) Fe2 (S04)3 (d) Al2 03
(Ca = 40, C=16, H = 1,
P=31, Fe = 56, S =32, Al = 27)
2. Determine the number of grammes of substance contained in 0.5 moles of hydrogen chloride gas (HCl) (Cl=35.5, H=1).