ANALYSIS OF A COMPOUND (EMPIRICAL AND MOLECULAR FORMULA)
A technique which is used to determine the unknown elements and their proportions in the given sample of a compound is called analysis.
Analysis is of two types:
(i) Qualitative analysis
(ii) Quantitative analysis
(i) Qualitative Analysis
A technique which is used to determine the unknown elements present in the sample of a compound is called qualitative analysis.
Example: Method used to determine C, H, and O in glucose.
(ii) Quantitative Analysis
A technique which is used to determine mass of each element in the sample of a compound is called quantitative analysis.
Example: The proportion of elements in Glucose (C6H12O6) C : H : O is 6 : 12 : 6
Percentage of an element:
Number of grams of an element in 100g of a compound is called percentage of that element.
Percentage of an element = x 100
For example, 6.92g of an element (carbon) and 1.73g of the second element (hydrogen) are present in 8.65g of the compound.
Percentage of an element = x 100
Percentage of the carbon = x 100
= 80%
Percentage of the hydrogen = x 100
= 20%
The percentage composition of above compound shows it to contain 80% carbon and 20% hydrogen.
Percentage composition of a compound can also be determined theoretically if we know the formula mass of the compound. The following equation can be used for this purpose.
Percentage of an element = x 100
Example: Percentage of hydrogen and carbon in CH4 can be calculated as.
Percentage of an element = x 100
Percentage of an carbon = x 100 = 75%
Percentage of an hydrogen = x 100 = 25%

Empirical Formula:
A formula which shows the simplest ratio between the atoms of the elements in the molecule of a compound is called empirical formula. e.g. H2O for water, CH for benzene (C6H6).
Steps to Determine Empirical Formula:
Empirical formula of a compound can be calculated by the following the steps:
(i) Determination of the percentage composition of each element.
(ii) Finding the number of gram atoms (mole) of each element. For this purpose divide the %age of an element by its relative atomic mass.
(iii) Determination of the atomic ratio of each element by dividing gram atoms or mole by the smallest number of moles.
(iv) If the atomic ratio is in simple whole number, it gives the empirical formula, otherwise multiply with a suitable digit to get the whole number atomic ratio.
Molecular Formula:
The formula of a substance which is based upon the actual ratio between the atoms in a molecule of a compound is molecular formula.
Examples:
C6H6 and C6H12O6 are the molecular formulas of benzene and glucose.
Relationship between empirical and molecular formula:
Molecular formula is integral multiple of empirical formula.
Molecular formula = n x Empirical formula
Where, ‘n’ is a simple integer.
(i) The value of n is greater than one for all those compounds which have different empirical formula and molecular formula. Molecular formula is simple multiple of empirical formula. e.g. n = 6 and n = 2 for benzene and acetic acid respectively.
(ii) The value of n is unity for all those compounds which have same empirical and molecular formula. e.g. n = 1 for water (H2O) and sucrose (C12H22O11).
EMPIRICAL FORMULA MOLECULAR FORMULA
Empirical formula shows the simplest ratio of atoms of the elements in a compound Molecular formula shows the actual number of atoms of elements present in a compound
It is used both for covalent and ionic compounds It is only used for covalent compounds
It is derived from chemical analysis It is obtained from empirical formula
Empirical formula =
Molecular formula = n x Empirical formula
e.g. for benzene ‘CH’, for glucose CH2O e.g. for benzene C6H6, for glucose C6H12O6