Page 129 - Chemistry ICSE Class X

Mole Concept and Stoichiometry 115
It is important to note that while using the unit mole, it is necessary to
Ϯϯ
specify the chemical unit also. ,Žǁ ďŝŐ ŝƐ ƚŚĞ ŶƵŵďĞƌ ϲ͘ϬϮ п ϭϬ ?
/ƚ ŝƐ ĐĞƌƚĂŝŶůLJ Ă ǀĞƌLJ ďŝŐ ŶƵŵďĞƌ͘ /ƚ
For example, ĐĂŶ ƉĞƌŚĂƉƐ ďĞ ǀŝƐƵĂůŝnjĞĚ ďĞƩĞƌ
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One mole of hydrogen atoms = 6.02 × 10 atoms of hydrogen ƚŚƌŽƵŐŚ ƚŚĞ ĨŽůůŽǁŝŶŐ ŝůůƵƐƚƌĂƟŽŶ͘
23
One mole of hydrogen molecules = 6.02 × 10 molecules of hydrogen ͻ
Ϯϯ
23
One mole of carbon dioxide = 6.02 × 10 molecules of carbon dioxide /Ĩ ǁĞ ƉůĂĐĞ ϲ͘ϬϮ п ϭϬ ĐƌŝĐŬĞƚ ďĂůůƐ
ĐŽǀĞƌŝŶŐ ƚŚĞ ĞŶƟƌĞ ƐƵƌĨĂĐĞ ŽĨ ƚŚĞ
23
One mole of electrons = 6.02 × 10 electrons ĞĂƌƚŚ͕ ďŽƚŚ ůĂŶĚ ĂŶĚ ǁĂƚĞƌ͕ ƚŚĞŶ
+
+
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One mole of sodium ions (Na ) = 6.02 × 10 Na ions ƚŚĞƐĞ ďĂůůƐ ǁŝůů ĨŽƌŵ ĂďŽƵƚ ϭϬϬ Ŭŵ
ƚŚŝĐŬ ůĂLJĞƌ ĂƌŽƵŶĚ ƚŚĞ ĞĂƌƚŚ͘
What is molar mass
Mass of one mole of any material is called its molar mass. The molar mass
is measured in the units of gram per mole (g/mol), or kilogram per mole
23
(kg/mol). One mole contains 6.02 × 10 chemical units. Therefore,
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Molar mass of a substance = Mass of 6.02 × 10 molecules of the substance
For example,
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Molar mass of hydrogen (H ) = Mass of 6.02 × 10 molecules of hydrogen
2
But,
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Mass of 6.02 × 10 molecules of a substance = Gram-molecular mass of that substance
and Gram-molecular mass of hydrogen = 2.016 g
So, Molar mass of hydrogen = 2.016 g/mol

What is molar volume
WůĞĂƐĞ ŶŽƚĞ ƚŚĂƚ ŝŶ ƚŚĞ ƚĞdžƚ ŽŶĞ ƵƐĞƐ
One mole of any gaseous substance at 273 K and 1 atmosphere pressure ƚŚĞ ǁŽƌĚ mole͕ ďƵƚ ǁŚĞŶ ƵƐĞĚ ĂƐ Ă
occupies a volume equal to 22.4 L or 22400 mL. The volume occupied by ƵŶŝƚ͕ ƚŚĞŶ ŝƚ ŝƐ ĚĞŶŽƚĞĚ ďLJ ƚŚĞ ǁŽƌĚ
one mole of any gaseous substance is called molar volume (V ). So, mol͘
m

It has been experimentally found that the molar volume of each gas
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(V ) contains 6.02 × 10 molecules. This number is called the Avogadro’s
m
number, and is denoted by N . Avogadro’s number is also called Avogadro’s
A
constant.
How many moles are there in a certain mass of a substance
We can calculate the number of moles in a certain mass of a substance by
using the formula,
Mass of the substance in grams
No. of moles of the substance, n =
Molar mass of the substance in grams per mole
W g W
n = = mol
M g/mol M
where, W is the mass of the substance.
M is the molar mass of the substance.
How many molecules are there in a certain mass of a
substance

We can calculate the number of molecules in certain mass of a substance by
using the formula,
Mass of the substance
No. of molecules in a sample = × Avogadro’s number.
Molar mass of the substance