How to Calculate Empirical and Molecular Formula

In this JC1 webinar let's learn how to calculate empirical and molecular formula of ascorbic acid or Vitamin C.

The empirical formula of a compound shows the simplest whole number ratio for the atoms of different elements present in the compound.

The molecular formula of a compound shows the actual number of atoms of the different elements present in the compound.

Let's take a look at the question.

calculate empirical and molecular formula question

Given the percentage mass, we can determine the mass of each element in 100g of ascorbic acid and calculate their number of moles.

calculate empirical and molecular formula mass in 100g and moles

We can then divide by the smallest value and round off to the simplest ratio to determine its empirical formula C3H4O3.

calculate empirical and molecular formula det ratio n EF

The molecular formula will be a multiple of the empirical formula, (C3H4O3)n.

The molar mass is given in the question and we can express the molar mass in terms of n, and hence solve for n.

calculate empirical and molecular formula det MF

Since n = 2, we can then deduce the molecular formula to be C6H8O6.

Topic: Mole Concept, Physical Chemistry, A Level Chemistry, Singapore

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