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Find out how to find the molecular formula of the compound. If you know the empirical formula of the compound it is easy to find its molecular formula.
What Will Be Given: Empirical Formula of Compound, Molar Mass of Compound
What To Calculate: Molecular Formula
Explanation :
The molecular formula of a compound is the exact number of atoms of each of its constituting elements found in the empirical formula.
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Steps to Calculate:
- If empirical formula of the compound is not given, see if percentage composition of elements is given. You need to find the empirical formula first to proceed.
- Find the empirical formula mass of the compound. This can be done by adding the atomic mass of each of the elements present in the compound.
- Use formula Molecular Mass = n x Empirical Mass to find out the value of n. Divide Molar Mass by Empirical Mass to get the value of n.
- Molecular Formula of the compound can be obtained by multiplying empirical formula by n.
Tips and Tricks
If the molecular mass of the compound is not given you can find it out by using following formulas.
a) Molecular Weight = 2 x Vapour Density
b) Molecular Weight = Weight of 22.4 L of gas at NTP
c) Molecular Weight = Weight of 1 mole
Example to calculate Molecular Formula
The empirical formula of the compound is C₂H₄O. The molecular mass of the compound is found to be 22. What is the molecular formula of the compound?
Step 1 is not required as empirical formula is given in the problem
As per step 2, find empirical formula mass
Empirical Formula Mass = 2 x 12 + 4 * 1 + 1 * 16
= 44
As per step 3
n = Empirical Mass / Molecular Mass
= 44/22
=2
As per step 4, multiply empirical formula by n
Molecular Formula = Empirical Formula x n
= C₂H₄O x 2
= C₄H₈O₂
Related Questions
- 0.45 g acid of molecular weight 90 was neutralise by 20 mL of 0.5 N KOH
- What is the molar ratio of mixture of gases given the ratio of gases
- The weight of one molecule of a compound C₆₀H₁₂₂ is
Subject: Chemistry (2512)
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