Question

What is a molecular formula?

Answer 1

• The molecular formula is the expression of the number of atoms of each element in one molecule of a compound.
• The molecular formula definition is the formula showing the actual number of each atom in a molecule.
• When the molar mass value is known, the Molecular Formula is calculated by the empirical formula.
• n = molar mass/mass of the empirical formula
• The molecular formula is often the same as an empirical formula or an exact multiple of it.

Example

• A compound contains 86.88% of carbon and 13.12% of hydrogen, and the molecular weight is 345.
• What will be the empirical and molecular formula of the compound?

To get the empirical and molecular formula of the compound following these steps

• Step 1

Multiply percent composition with the molecular weight

Carbon : 345 x 0.8688 = 299.736

Hydrogen : 345 x 0.1312 = 45.264

• Step 2

Divide each value by the atomic weight

Carbon : 299.736 / 12.011 = 24.995

Hydrogen : 45.264 / 1.008 = 44.91

Round off the values to closest whole number so that on next step

• Step 3

Molecular formula is C₂₅H₄₅

• Step 4

Since 5 is the common factor, the empirical formula is C₅H₉