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Empirical Formular

Updated on October 22, 2011

Empirical formula can help you to predict a chemical compound from simple calculations. Here you will find an explanation of what empirical formula is, how to calculate empirical formula, and the calculation of the empirical formula of glucose as a potent example.

What is empirical formula?

Empirical Formula of a chemical compound is the simplest formula of that compound. It is used in analytical chemistry, during elemental analysis, to express the smallest amount of each of the elements in the chemical compound that is under investigation. The empirical formula of a chemical compound presents the constituent elements in that compound in the simplest ratio possible, so that the molecular formula becomes a multiple of the Empirical formula in most cases.

While the Empirical Formula of certain chemical compound, such as Benzene (C6H6), is expressed in actual small ratio of the chemical compound (CH), Ethanol (C2H5OH) on the other hand has its empirical formula exactly the same as its chemical formula.

It must also be noted that Empirical formula does not cater for structural chemical characteristics. Neither does it expand into Isomerism. It is simply a mathematical tool used to express results drawn from an experiment.

Video: How to calculate empirical formula

Calculation of empirical formula

The chemical components of the results obtained from the elementary analysis of chemical compounds are usually expressed in percent %. Hence, each element must be divided by the relative molecular mass (M) of that element. i.e. %/M. And the smallest result must be used to divide all the results obtained in other to present it in the smallest ratio.

Let's say the result obtained for elements 1, 2, 3 is %/M1=x, %/M2=y, %/M3=z respectively, and element 1 has the smallest result, then, the ratio would be: x/x, y/x, z/x respectively. Hence the Empirical formula is the value obtained from the ratio expressed as the quantity of that element in the smallest formula of the compound. Actual mathematical approach can be used to show the calculation of the empirical formula of Glucose as evident below.

Calculation of empirical formula of glucose

Glucose is made up of Carbon (C), Hydrogen (H), and Oxygen (O). The percentage composition of each of the elements is: C - 40%, H - 6.67%, and O - 53.33%.

The relative molecular mass of each of the elements in the glucose molecule is as follows: Carbon - 12, H - 1, and O - 16.

To calculate the empirical formula of glucose, we must divide the percentage composition of the elements by their respective relative molecular masses and express the result in the ratio of the simplest component

C : H : O = 40/12 : 6.67/1 : 53.33/16 = 3.33 : 6.67 : 3.33

The smallest value is 3.33. This implies that we must divide through by 3.33.

= 3.33/3.33 : 6.67/3.33 : 3.33/3.33 = 1 : 2 : 1

The implication is that, Glucose contains one carbon atom, two Hydrogen atoms, and one Oxygen atom in its empirical formula, thus the result CH2O.


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