Percentage Composition | Some Basic Concepts Of Chemistry | Praadis Education
As we know that a chemical compound is formed by combining two or more elements into one substance through a chemical reaction. We can determine the structure of an unknown compound with the help of percentage composition.
We can compare the percentage composition obtained experimentally and the theoretical value calculated from the compound’s formula and by comparing this we can test the purity of compounds. It means we can check the purity of a given sample by analyzing this data.
Until now, we were dealing with the number of entities present in a given sample. But often, information about the percentage of a particular element present in a compound is essential.
The ratio of the amount of each element present in the compound to the total amount of individual elements in the compound, which is then multiplied by 100 is known as the percentage composition of any given compound. Here, we calculate the quantity of the elements present in the solution in terms of grams.
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To calculate the percentage composition of any given element we can use the formula as mentioned below:
%CE=gE/gT×100
Here,
Element is represented by ‘E’,
The percentage composition of the element E is represented by ‘% CE’,
On the right side of the equation, the numerator represents the total amount of element E present in the compound i.e. gE and
The denominator represents the total amount of all the elements present in the compound I.e. gT
And by multiplying this ratio by 100 we will get the percentage composition.
Now let us understand this by taking the example of water.
The chemical formula of water is H2O.
Water consists of two molecules of hydrogen,
and one mole of water = 18.0152 grams.
So, 2 hydrogen moles weigh = 2.016 grams.
Hence, one mole of water consists of 2.016 grams of hydrogen mole.
Therefore, the percentage composition of hydrogen =
2.016/18.0152 = 11.19%.
Mass % of an element = (mass of that element in the compound×100) ÷ molar mass of the compound
Mass % of hydrogen = (2×1.008 ÷ 18.02) × 100 = 11.18
Mass % of oxygen = (16.00 ÷ 18.02) × 100 = 88.79
