Percentage Composition: Definition, Calculation, and Types

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What is Percentage Composition?

The percentage composition of any given compound is defined as the ratio of the amount of each element present in the given compound to the total amount of individual elements present in that particular compound multiplied by 100. The importance of this composition calculation is found in the chemical analysis.

Percentage Composition Formula

The percentage composition of a given element can be expressed by using the formula given below:

% of an element = (mass of element/molecular mass) x 100

The reason that we multiply this ratio by 100 is to get the percentage form of the given composition.

Percent composition is calculated from a molecular formula that is by dividing the mass of a single element in one mole of a compound by the mass of one mole of the whole given compound. This value is presented in the form of a percentage.

How to Calculate Percentage Composition?

Calculate the percent composition of each element in water.

The chemical formula for water is written as H2O and The molar mass of Oxygen is = 16.00 × 1(one molecule of oxygen is present in water) = 16 g/mole and the molar mass of Hydrogen is = 1.01 × 2(2 molecules of hydrogen are present in water) = 2.02 g/mole

Now, with the help of the molar mass of each of the given elements, find the percentage composition of each element present in H2O.

It is defined as the ratio of the grams of the element to the grams of the total element in that particular compound, multiplied by 100.

Thus, calculating the percentage composition of Hydrogen,

% H = 2.02/18.02 × 100


% H= 11.21 %

The percentage composition of Oxygen is calculated, So,

% O = 16/18.02 ×100 = 88.79 %

Mass Percentage Composition

The concept of mass percentage composition is used to represent the concentration of an element in a compound or the concentration of a component in a given mixture. We use this term to indicate the total percent by mass of each element that is present in a given compound.

The mass percentage composition can be calculated by dividing the mass of a component by its the total mass of the mixture. This ratio obtained is then multiplied by 100.

Importance of Mass Percentage

For many technical and scientific reasons, it is important to know what quantity of an element is present in an assumed compound.

This is crucial for pharmacists to get to the empirical formula of some compounds.

This formula also helps in displaying the lowest whole number of moles and the relative quantity of atoms of each element present in a particular compound.

With the help of this empirical formula, pharmacists can also calculate the actual molecular formula which shows the exact number of atoms present in the given compound.

Determining the Mass Percent from a Chemical Formula

Calculate the mass percent of glucose.

The chemical formula for glucose is written as C6H12O6. Now, calculate the mass percent of each of the elements present in glucose.

From the formula mentioned above, it can be observed that Glucose consists of 6 carbon atoms, 12 hydrogen atoms, and at last 6 oxygen atoms. Now multiply each of the atoms present in the glucose molecule by its molar mass.

So, 6 moles of carbon have 12.01g/mol x 6 = 72.06g of Carbon. (1 mole of carbon has a mass of 12.01grams)

Consequently, 12 moles of Hydrogen will have a mass of 12 x 1.008 = 12.096g of Hydrogen. (1 mole of hydrogen has a mass of 1 gram)

Thus, 6 moles of oxygen will have 16.00 x 6 = 96 g of Oxygen. (1 mole of oxygen has a molecular mass of 16 gram)

Hence, 1 mole of glucose (C6H12O6) has a total mass of (adding all the above values); 72.06 +12.096 + 96 = 180.16 g/mol

Percentage Composition Citations


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