In the previous blogpost, we have discussed on the Common Errors on Calculating Empirical Formula, when given Composition by Mass. Today we shall go one step further and see how we can determine the Molecular Formula from an Empirical Formula.
The Molecular Formula shows all the atoms of each element contained in one molecule.
Empirical Formula shows the simplest ratio of the different types of elements present in a molecule.
For example, Hexane has Molecular Formula of C6H12 and Empirical Formula of CH2.
As such, Molecular Formula is a simple multiple of the Empirical Formula:
Molecular Formula = n X Empirical Formula
where n = 1, 2, 3, etc
The molecular formula can be calculated from:
Let’s take a look at an example.
Example:
Glucose has empirical formula CH2O and relative molecular mass of 180. Find the molecular formula of glucose.
(given: H = 1.0; C = 12.0; O = 16.0)
Suggested Answer:
Relative mass of Empirical Formula, CH2O = 12 + 2(1) + 16 = 30
Relative molecular mass = n X relative mass of the empirical formula
thus, n = Relative molecular mass / relative mass of the empirical formula
= 180 / 30 = 6
Therefore, Molecular Formula of Glucose = 6 X CH2O = C6H12O6
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