Question

Define an empirical formula.

Answer 1

The empirical formula provides the idea about the lowest whole number ratio in which atoms are exiting in the compound. It does not give any idea about the arrangement of the atoms in the compound. It is the relative ratio of elements in a compound. For example, an empirical formula $\text{ }{{\text{P}}_{\text{4}}}{{\text{O}}_{\text{10}}}\text{ }$ is equal to $\text{ }{{\text{P}}_{2}}{{\text{O}}_{5}}\text{ }$ . Since, there is scope for further simplification of formula as $\text{ }\dfrac{\text{4}}{2}\text{ : }\dfrac{\text{10}}{2}\text{ }\Rightarrow \text{ 2 : 5 }$

Complete step by step solution:
The empirical formula is the simplest integer ratio in which atoms combine. The relative number of atoms in the compound is explained by considering the empirical formula. The following are the step used for the determination of empirical formula,

1. First write down the number of grams each element provides to us.
2. We will consider that, the total mass of the compound formed after the combination of elements is equal to 100 grams and masses are provides in the percentage consider $\text{ 100}{\scriptstyle{}^{0}/{}_{0}}\text{ }$
3. In this step, find out the number of moles of the element by the formula $\text{ number of moles = }\dfrac{\text{Given mass }}{\text{Molar mass }}$
4. Divide the moles of the element by the lowest value of the mole computed.
5. Round up the obtained values to the closest whole number and denote this as the subscript concerning each element.
6. If subscripts can be further simplified do so and we have the empirical formula for the compound.
   Let's consider the examples of the empirical formula of compounds.
   i) Empirical formulas of hydrogen peroxide $\text{ }{{\text{H}}_{\text{2}}}{{\text{O}}_{\text{2}}}\text{ }$ is $\text{ }{{\text{H}}_{\text{1}}}{{\text{O}}_{\text{1}}}\text{ }$ as there is one oxygen for one hydrogen $\text{ (1:1) }$
   ii) Empirical formulas for $\text{ Mg(N}{{\text{O}}_{\text{3}}}{{\text{)}}_{\text{2}}}\text{ }$ is, $\text{ Mg}{{\text{N}}_{\text{2}}}{{\text{O}}_{\text{6}}}\text{ }$
   Always remember that the relative ratio is always the whole number.

Note: The molecular formula expresses the arrangement of the toms in the compound but the empirical formula does not. For example, glucose $\text{ (}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}\text{)}$ , acetic acid $\text{ (}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{{\text{O}}_{\text{2}}}\text{)}$ , formaldehyde $\text{ (C}{{\text{H}}_{\text{2}}}\text{O) }$ have different molecular formulas but have the same empirical formula $\text{ C}{{\text{H}}_{\text{2}}}\text{O }$ .So do not get confused with the empirical formula and molecular formula.