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Question

How do you find the molecular formula of a compound?


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Solution

Molecular formula:

  1. A molecular formula is a chemical notation that indicates the number and kind of components present in a single molecule of a substance.
  2. The simplest form of the molecular formula is the empirical formula. It can figure out what amounts each constituent in the molecule should be in.
  3. The Molecular formula empirical=n×empirical formula, where n is an integer multiple.

Example:

  1. For calculating molecular formula let us take a compound having 49.48%carbon, 5.19%hydrogen,16.48% oxygen, and 28.85% nitrogen. The molecular weight of the compound=194.19gmol-1.

Step 1: Calculating the weight of the particular atom

Multiplying percent composition by weight we get,

Carbon=194.19×0.494896.0852

Hydrogen=194.19×0.051910.0784

Oxygen=194.19×0.164832.0025

Nitrogen=194.19×0.228556.0238

Step 2: Dividing each value by its atomic weight

Carbon=96.085212.0117.9997

Hydrogen=10.07841.0089.998

Oxygen =32.002515.99942.000

Nitrogen=56.023814.00673.9997

Step 3: Rounding off to the closest whole number:

Carbon=7.9978

Hydrogen=9.99810

Oxygen=2

Nitrogen=3.9974

Step 4: Writing molecular formula:

Write each value of the whole number along with its atom.

We get the molecular formula asC8H10O2N4.


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