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Empirical Formula

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  • Last Updated : 15 May, 2022
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Chemical formulas are obtained by determining of masses of all the elements that are combined to form a molecule/compound. There are two important types of formulas in chemistry. They are Molecular formulas and Empirical formulas. The molecular formula of a compound gives the actual number of each different atom present in a molecule, whereas the Empirical formula gives the simplest ratio of the number of each different atom in a compound. Simplification of the molecular formula gives empirical formula. There is a relationship between molecular formula and empirical formula, which is given by,

Molecular Formula = n × Empirical Formula

Where n is a whole number

Empirical Formula

The empirical formula is the simplest formula for a compound. It is defined as the ratio of subscripts of the smallest possible whole number of the elements present in the formula. This formula gives information about the ratio of the number of atoms in the compound. To get a better understanding of the empirical formula, let’s look into a few examples,

The molecular formula of acetylene is C2H2.

The empirical formula is the simplest ratio of a number of each different atom present in the compound.

Molecular Formula = n × Empirical Formula

C2H2 = 2 × CH

So, the Empirical formula of acetylene is CH.

Sample Questions

Question 1: The Empirical formula of Butane is C2H5. Calculate the Molecular formula when the measured mass of the compound is 58.1224

Solution:

The atomic mass of given empirical formula = 2(C) + 5(H) = 2(12.011) + 5(1.00784) = 29.0612u

But, the measured molecular mass for Butane is given as 58.1224u

By using the expression, Molecular formula = n × empirical formula

n = weight of molecular formula/weight of empirical formula

= 58.1224/29.0612

= 2

Molecular formula = 2 × C2H5

= C4H10

Question 2: Why do we use Empirical Formula?

Answer:

Empirical Formula represent the simplest notation to a compound. It provide the lowest ratio of whole numbers between the elements of a compound. Unlike molecular formula it doesn’t specify the total number of atoms present in the compound.

Question 3: Find a molecular formula for the compound having the empirical formula CH2 with a molecular weight of 42.08.

Answer:

The atomic mass of given empirical formula = C + 2(H) = 12.011 + 2(1.00784) = 14.02u

But, the measured molecular mass for given compound is 42.08u

By using the expression, Molecular formula = n × empirical formula

n = weight of molecular formula/weight of empirical formula

= 42.08/14.02

= 3

Molecular formula = 3 × CH2

= C3H6

Question 4: What is the difference between Molecular Formula and Empirical Formula?

Answer:

Molecular Formula specifies the actual number of atoms of different elements in a compound. In the other side, Empirical Formula gives the simplest ratio of number of each different atom in a compound.

Question 5: Find the empirical for the compound with molecular formula C6H12O6.

Answer:

C6H12O6 = 6 × CH2O

we know that Molecular Formula = n × Empirical Formula

Here n = 6

So empirical formula for the given compound is CH2O.

Question 6: Give the formula for Empirical Formula.

Answer:

Using the molar mass convert the mass of each element into moles. Then divide each mole value by the smallest calculated number of moles. Round the number to closest real number if it is not a real number. The resultant is the mole ratio of the elements and is represented by subscriptions in the empirical formula.

Question 7: What is the use of an Empirical Formula?

Answer:

Empirical formula is generally used to simply show what elements are present in a molecule. This is useful when one wants to know at a glance about what elements they are dealing with.

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