Question

Give the empirical formula of:
1. Benzene (${ C }_{ 6 }{ H }_{ 6 }$)
2. Glucose (${ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }$)
3. Acetylene (${ C }_{ 2 }{ H }_{ 2 }$)
4. Hydrogen peroxide (${ H }_{ 2 }{ O }_{ 2 }$)

Answer 1

Hint: An empirical formula is the reduced form of the molecular formula. It represents the simplest ratio of the elements of a particular compound.

Complete answer:
An empirical formula of a molecule exhibits the simplest ratio of the elements in a molecule. An empirical formula of a compound can be represented by the lowest whole number ratio of the elements in a molecule.
The main difference between an empirical formula and a molecular formula of a compound is that the molecular formula implies how many atoms of each element are present in a molecule, whereas, an empirical formula implies the reduced ratio of elements present in a molecule.
The most widely used procedure to determine the empirical formula of a compound is the combustion analysis. The molecular formula of a molecule can be evaluated from the empirical formula.
If we have the molecular formula of a compound, then we can find out the empirical formula with the help of molecular formula.
In order to find out the empirical formula from the molecular formula, we have to execute the following steps:
* We have to identify the atoms present in the molecule.
* Then, we have to find out the greatest common factor (GCF) of the subscripts written in the molecular formula.
* Then, we have to divide the subscripts by the GCF.
* Then, we have to write the atoms along with the new subscripts (which we have got after division).
* This will be our reduced ratio of the elements of that compound.

By following the above steps, let’s determine the empirical formulas of the given compounds.
Benzene $C_6 H_6$
* The atoms are: C and H.
* The GCF of the subscripts is 6.
* After dividing the subscripts by 6, we will get 1 for each atom.
Hence, the empirical formula of benzene will be CH.
Glucose (${ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }$)
* The atoms are C, H, and O.
* The GCF of the subscripts is 6.
* After dividing the subscripts by 6, we will get 1 for C and O and 2 for H.
Hence, the empirical formula of glucose will be $CH_2O$.
Acetylene (${ C }_{ 2 }{ H }_{ 2 }$)
* The atoms are C and H.
* The GCF of the subscripts is 2.
* After dividing the subscripts by 2, we will have 1 for both C and H.
Hence, the empirical formula of acetylene will be CH.
Hydrogen peroxide (${ H }_{ 2 }{ O }_{ 2 }$)
* The atoms are H and O.
* The GCF of the subscripts is 2.
* After dividing the subscripts by 2, we will get 1 for both H and O.
Hence, the empirical formula of hydrogen peroxide will be HO.
Note: While determining the empirical formula of a molecule, students have to remember that they have to calculate the highest common factor of the subscripts, not the LCM (lowest common multiple). Otherwise, it will lead to a wrong empirical formula.