Page 145 - Chemistry ICSE Class X

Mole Concept and Stoichiometry 131

What is meant by gram-ion mass
In terms of the mole concept, the gram-ion mass of an ion is equal to the
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mass (in gram units) of 6.02 × 10 ions of that type. Since the number
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6.02 × 10 is termed as the Avogadro’s number of that ion,
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1 gram-ionic mass = 1 gram-ion = Mass of 6.02 × 10 ions = Mass of Avogadro’s number of that ions
ASSIGNMENT 3

Atomic and relative atomic masses, Molecular mass and relative molecular mass,
Formula mass, Gram-atomic mass, Gram-molecular mass

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; ƚŽŵŝĐ ŵĂƐƐĞƐ͗ ,LJĚƌŽŐĞŶ с ϭ͘Ϭ͕ EŝƚƌŽŐĞŶ ϭϰͿ

Composition of a Compound

# EQORQWPF EQPVCKPU VYQ QT OQTG GNGOGPVU EQODKPGF KP C EGTVCKP ſZGF
ratio. The composition of a compound can be described by the mass
percentage of each element present in it. This may be determined by any of
the methods described below.

How to determine the composition of a compound
Composition of a compound is commonly expressed as the mass percentage
of each element present in it. To determine the mass percentage of an element
in any compound, we should know the mass of that element present in a
certain known mass of the compound.
Let us suppose, W g of a compound contain w g of an element A.
Then,
Mass percentage of the element A = Mass of element A × 100
Mass of the compound
w g w
= × 100 = × 100
W g W
To do this, a known mass of the compound is chemically analysed, and
the mass of each element present in it is determined by a suitable chemical
method.
EXAMPLE 5.16. 5.85 g of a compound contains 3.55 g of chlorine, and 2.30 g of
sodium. Determine the mass percentage of sodium and chlorine in the compound.
Solution: Mass of the compound = 5.85 g
Mass of sodium = 2.30 g
Mass of chlorine = 3.55 g

Then,
Mass percentage of sodium = Mass of sodium × 100 = 2.30 g × 100 = 39.3
Mass of the compound 5.85 g
Mass of chlorine 3.55 g
Mass percentage of chlorine = × 100 = × 100 = 60.7
Mass of the compound 5.85 g
Thus, mass percentage of sodium and chlorine in the given compound are 39.3 and 60.7, respectively.