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Chemical Formulae and Equation
B. The mole and thenumber of particles
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The Concept of Mole
According to SI ( International System of Units)
One mole is an amount of substance that contains
as many particles as the number of atoms in
exactly 12.000 g carbon-12, which is 6.02 x 1023particles.
1 mol = 6.02 x 1023particles
= 602 000 000 000 000 000 000 000 particles
The value of 6.02 x 1023 also recognized as theAvogadro
constant, NA.
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Avogadro Constant
Avogadro Constant is defined as the number of
particles in one mole of a substance which is
6.02 x 1023
mol1
.This means:
1 mole of iron = 6.02 x 1023 iron atoms
1 mole of water = 6.02 x 10
23
water molecules1 mole of ammonia = 6.02 x 1023ammonia
molecules
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CautionThe particles need to be carefully specified
ATOM IC SUBSTANCES
All metal eg sodium, copper, iron
All noble gases eg helium, argon, neon
Certain non-metals element eg. carbon & silicon
MOLECULAR SUBSTANCES
some non-metal element eg H2, O2, F2. Cl2, S8, P4
All covalent compound eg water and carbon dioxide.
IONIC SUBSTANCES
All ionic compounds eg. Sodium chloride, zinc bromide
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Mole and the Number of Particles
Number
of Mol
Numberof
Particles
Avogadro constant
Avogadro constant
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Example of Calculation 1
Calculate the number of particles contain
in 0.4 mol of chlorine atom .
Solution
Number of chlorine atom
= number of moles x NA
= 0.4 x 6.02 x 1023
= 2.408 x 1023 atom
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Example of Calculation 2
Calculate the number of moles represented
by 1.204 x 1023sodium atom.
Solution:
mol2.0
1002.6
10204.1
N
atomsodiumofNumber
atomsodiumofmolesofnumberThe
23
23
A
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Example of Calculation 3
Calculate the number of molecules that
contain in 0.05 moles of iodine, I2 .
Solution:
The number of iodine, I2 molecule
= number of moles x NA= 0.05 x 6.02 x 1023molecules
= 3.01 x 1022 molecules
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Particles in Molecular Substance
No. of moles
molecular
substance
No. of
moleculeNo of atom
NA
NA
( depends on
chemical formula )
( depends onchemical formula )
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Particles in Ionic Substance
No. of moles
ionic
substance
No. of Unit No of ions
NA
NA
( depends on
chemical formula )
( depends onchemical formula )
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Example of Calculation 1
Calculate the number of fluorine atom contains in 0.3 mol
offluorine gas, F2.
Solution:The number of fluorine molecules, F2
= number of moles x NA
= 0.3 x 6.02 x 1023
1 molecule of F2 = 2 fluorine atom
The number of fluorine atom, F= 2 x 0.3 x 6.02 x 1023
= 3.612 x 1023
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Example of Calculation 2
A sample of ammonia gas contains of
1.806 x 1024molecules of ammonia.
Calculate the number of
a)moles of ammonia
b)nitrogen atomc)Moles of hydrogen atom
that contain in the sample
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Solution
mol3
1002.6
10806.1
N
moleculeNHofNumber
moleculesNHofmoles)a(
23
24
A
3
3
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Solution
(b) A molecule of ammonia, NH3 consists
1 nitrogen,N atom
Thus,
1.806 x 1024molecules of ammonia
consists 1.806 x 1024 nitrogen atom
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Solution
(c) A molecule of ammonia, NH3 consists 3
hidrogen,H atom1 mole of NH3molecule 3 moles of H atom
3 moles of NH33 3 moles of H atom
9 moles of H atom
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Example of Calculation 3
Calculate the number of hydroxide ions in 0.5 mole
of magnesium hydroxide, Mg(OH)2.
Units of Mg(OH)2= 0.5 x NA
= 0.5 x 6.02 x 1023
1 unit of Mg(OH)2consists of 2 hydroxide(OH) ions
Thus,
Number of hydroxide ions, OH= 2 x 0.5 x 6.02 x 1023
= 6.02 x 1023
