Question

What is the empirical formula for vitamin C.
$1.{\text{ C}}{{\text{H}}_2}O$
$2.{\text{ }}{{\text{C}}_3}{{\text{H}}_4}{{\text{O}}_3}$
$3.{\text{ }}{{\text{C}}_6}{{\text{H}}_8}{{\text{O}}_6}$
$4.{\text{ CHO}}$

Answer 1

Empirical formula is one which gives the smallest whole number of the atoms or mole ratio of atoms present in the compound. The empirical formula gives the lowest whole number ratio of the elements in the compound. Vitamin C is an organic compound so it must contain carbon, hydrogen and oxygen.

Complete answer:
The empirical formula sometimes is not the same as the molecular formula. For ionic compounds it may be some but for organic compounds it may differ from the actual molecular formula. So we can calculate the empirical formula in the following ways when mass percentage is given:
$1.$ When we are given the mass percentage of the atoms of the compound.
$2.$ Convert the mass percentage into grams of each element by assuming the $100{\text{ g}}$ sample.
$3.$ Now use the molar mass of the compound and then find the moles of each element.
$4.$ Now calculate the mole ratio of each element and hence find the empirical formula.
Thus we can find the empirical formula for Vitamin C too when mass percentage is given. Therefore the empirical formula of the vitamin C is found to be ${C_3}{H_4}{O_3}$.
If we are given the molecular mass of the compound we can find its molecular formula also.
Molar mass of compound $=$ whole number multiple $\times$ empirical mass of the compound.

Note:
Vitamin C is also known as ascorbic acid. We must assume $100{\text{ g}}$ of the sample because it is easier to find the mass from the mass percentage of each element in the organic compound. For finding the mole ratio we use the unitary method.