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Empirical and Molecular Formula - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main
Quick Facts
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Empirical Formula And Molecular Formula is considered one of the most asked concept.
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30 Questions around this concept.
Solve by difficulty
6 litres of an alkene require 27 litre of oxygen at constant temperature and pressure for complete combustion . The alkene is:
A cubic solid is made up of elements R and Q. R is at $\frac{1}{3}^{\mathrm{rd}}$ the id of the total faces and Q is present on every alternate corner. The empirical formula of a compound is
Compound with molar mass given as 180 grams having an empirical formula as $\mathrm{CH}_2 \mathrm{O}$ . Find the correct molecular formula ?
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Empirical formula of Acetic Acid ?
Two isomers (A) and (B) with Molar mass $184 \mathrm{~g} / \mathrm{mol}$ and elemental composition $\mathrm{C}, 52.2 \% ; \mathrm{H}, 4.9 \%$ and $\mathrm{Br}, 42.9 \%$ gave benzoic acid and p-bromobenzoic acid, respectively on oxidation with $\mathrm{KMnO}_4$. Isomer ' A ' is optically active and gives a pale yellow precipitate when warmed with alcoholic $\mathrm{AgNO}_3$. Isomer ' A ' and ' B ' are, respectively
The reaction of an alkene X with bromine produces a compound Y, which has 22.22% C, 3.71% H and 74.07% Br. The ozonolysis of alkene X gives only one product. The alkene X is:
[Given: atomic mass of C = 12; H = 1; Br = 80]
The emipirical formula of a compound is CH2O . If its VD is 30 , then its molecular formula is :
Concepts Covered - 1
Empirical Formula And Molecular Formula
Chemical Formula:
A chemical formula represents the combination of atoms of all the elements which make up a compound. It represents the relative ratio of atoms of its constituent elements. In case of a compound, it represents one molecule, one mole, one gram molecular weight of the compound.
Example, CuSO4.5H2O represent one molecule, one mole and one gram molecular weight of hydrated copper sulphate.
Empirical Formula:
It is the simplest ratio of the number of atoms of different elements present in one molecule of a compound. It does not represent the actual number of atoms of different elements present in one molecule of the compound.
How to find out the empirical formula and the molecular formula in case the % composition of the compound is given to us
Step 1. Conversion of a mass percent to grams.
Step 2. Convert grams into the number of moles of each element.
Step 3. Divide the mole value obtained above by the smallest number.
Step 4. Write the empirical formula by mentioning the numbers obtained above after writing the symbols of respective elements.
Step 5. Write molecular formula (Molecular formula) with the help of the information given.
Molecular formula is a whole number multiple of the empirical formula
where n is whole number.
Molecular Formula:
It shows the actual number of atoms of different elements present in one molecule of a compound.
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n = (Molecular weight) / (Empirical formula weight)
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Molecular weight can be directly given or some other information like Vapour density can be given which will enable us to calculate the molecular weight.
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Molecular weight = 2 x Vapour Density
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For some compounds the molecular formula and empirical formula may be same also.
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