**What is Percentage Composition?**

Percentage composition is defined as ” the number of parts of an element in 100 parts of a compound “

Or in simple words:

The percentage amount of all elements in the compound is called percentage composition.

** Percentage Composition Calculation Formulae:**

** %age of element **= Mass of element in the compound X 100

Mass or molar mass of compound

OR:

** %age of element** = Atomic mass X Number of moles X 100

molar mass of compound

OR:

** %age of element** = Atomic mass X Number of atoms X 100

molar mass of compound Avogadro’s number

Related Important Question:

** What is the percentage composition of water?**

The percentage composition of water can be calculated as follow:

**Molar mass of water (H _{2}O)**= ( 2 X1) + (1 X 16)

= 2+ 16

= 18 g/mol

we know that :

** %age of element **= Mass of element in the compound X 100

Mass or molar mass of compound

** %age of H **= 2 X 100

18

= 11.11%

** %age of O **= 16 X 100

18

= 88.89%

*Numerical*s:

*Numerical*s:

Aluminium sulphate hydrate [Al_{2}(SO_{4})_{3}.x H_{2}O] contains 8.20% of Al by mass, calculate x.

*Solution*:

Formula mass of Al_{2}(SO_{4})_{3}.x H_{2}O = 27×2 + 32×2 + 16×12 + x(1×2 + 16)

or Formula mass of Al_{2}(SO_{4})_{3}.x H_{2}O = 54 + 96 + 192 + x(18)

or Formula mass of Al_{2}(SO_{4})_{3}.x H_{2}O = 342 + 18x

Percentage of Al in Al_{2}(SO_{4})_{3}.x H_{2}O = 8.20%

But Percentage of Al in Al_{2}(SO_{4})_{3}.x H_{2}O = Amount of Al in Al_{2}(SO_{4})_{3}.x H_{2}O x 100

Formula mass of Al_{2}(SO_{4})_{3}.x H_{2}O

8.20 = 54 x 100

342 + 18x

Or 8.20 (342 + 18x) = 5400

Or 2804.40 + 147.60x = 5400

Or 147.60x = 5400- 2804.40

Or 147.60x = 2595.60

Or ** x = 2595.60 / 147.60 = 17.59 ≈ 18**

Q. Calculate the percentage composition of a compound. ( MgSO_{4} )

Molar mass of MgSO_{4} = 1 x 24 + 1 x 32 + 4 x 16 = 24 + 32 + 64 = 120

% age of Mg = Mass of Mg x 100 = 24 x 100 = 20 %

** **Molar mass of MgSO_{4} 120

% age of S = Mass of S x 100 = 32 x 100 = 26.67 %

** **Molar mass of MgSO_{4} 120

% age of O = Mass of O x 100 = 64 x 100 = 53.33 %

** **Molar mass of MgSO_{4} 120

Categories: chemistry, Stoichiometry