Monday, 29 December 2014

3.2 The Mole and the Number of Particles

The number of moles and the number of particles
Definition : Mole: One mole is the amount of any substance which contains the same number of particles as there are in 12g of Carbon-12, that is 6.02×1023 or the Avogrado constant.
■ Relationship between number of moles and number of particles.

1 mole of any substance contains 6.02×1023 particle of that substances (atoms, molecules or ions).

For atom :
1 mole of lithium (Li) : 6.02×1023 atoms of lithium
1 mole of carbon (C) : 6.02×1023 atoms of carbon

For molecule:
1 mole of hydrogen ( H2 ) : 2×6.02×1023 atoms of hydrogen or 6.02×1023 molecules of hydrogen.
1 mole of carbon dioxide ( CO2 ) : 3×6.02×1023 atom or 6.02×1023 molecules of carbon dioxide.


For ion:
1 mole of sodium chloride (NaCl) : 6.02×1023 ions Na+ and 6.02×1023 ions Cl-
1 mole of zinc bromide ( ZnBr2 ) 6.02×1023 ions Zn+ and 2×6.02×1023 ions Br-

■ Summary of relationship between number of moles and number of particles.
Worked-example 3.2(a)
Calculate the number of particle in

(a) 0.5 mole of Copper

Solution
Number of particle in 0.5 mole of copper
=0.5×6.02×1023
=3.01×1023 atom

(b) 0.25 mole Lead(II) ions, Pb2+

Solution
Number of particle in 0.25 mole of Lead(II) ions,
=0.25×6.02×1023
=1.505×1023 ion Pb2+

(c) 3.0 moles Carbon Dioxide,

Solution
Number of particle in 3.0 moles of Carbon Dioxide
=3.0×6.02×1023
=1.806×1024 molecule CO2

Worked-example 3.2(b)
Calculate the number of moles of the following substances

(a) 1.505×1024 atom of Silver, Ag

Solution
Number of moles
=1.505×1024 6.02×1023
= 2.5 mol

(b) 3.01×1022 Oxide ions, O2-

Solution
Number of moles
=3.01×1022 6.02×1023
= 0.5 mol

(c) 4.515×1024 Nitrogen molecules, N2

Solution
Number of moles
=4.515×1024 6.02×1023
= 7.5 mol of molecules N2


Worked-example 3.2(c)

(a) Find the number of atoms in 1.5 moles of Cl2

Solution
1.5 =Number of molecules 6.02×1023
Number of molecules = 1.5×6.02× 1023
Number of molecules = 9.03×1023
Number of atom = 2×9.03×10 23
Number of atom = 1.806×1024 atom

(b) Find the number of ions in 0.5 mole of Magnesium Chloride, MgCl2

Solution
0.5 =Number of particles 6.02×1023
Number of particles = 0.5×6.02× 1023
Number of particles = 3.01×1023
Number of ions = 3×3.01×1023
Number of ions = 9.01×1023


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