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How to determine the formula of an unknown compounds ?

A large number of compounds are prepared in chemical laboratories. The chemists have to identify the compounds and determine their formulae. The formula of a compound is determined in the following steps:

Chemical structures of studied compounds. : Halofuginone and other ...

Image Source: nature.com/nchembio/journal/v8/n3/images/nchembio.790-F1.jpg

Step-1

Identification of elements present in the compound. The elements present in the compound are identified by different experimental tests.

Step-2

The percentage composition of the compound is determined by various techniques whose discussion is beyond the scope of this book.

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The mass of each element present in the compound is expressed in terms of percentage by mass. This is done by using the formula,

percentage composition = Mass of the element x 100/ total mass of the compound

Step-3

The empirical formula can be calculated from the percentage composition of each element present in the compound if the atomic mass of each element is known.

(i) The percentage mass of each element is divided by its atomic mass. This gives the relative number of atoms of various elements present in the compound.

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(ii) Each of the above figures is divided by the smallest figure amongst them. This gives the simplest ratio between the various atoms present. From this, the empirical formula can be calculated.

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