Question

The percentage composition of sodium phosphate as determined by analysis is 42.1% sodium, 18.9% phosphorus and 39% oxygen. Find the empirical formula of the compound.[Na=23, P=31, O=16.

Answer 1

Hint: By finding the mass percent of various elements present in the compound like here we have sodium, phosphorus and oxygen we can find the empirical formula. The simplest positive integer number of the atoms contained in a compound is the empirical formula of a chemical compound.

Complete answer:
We take percentage composition so that one can check the purity of a given sample by analysing the data, so to find the percentage composition we can calculate it by the formula which is as follows:
Mass % of an element = $\dfrac{Mass\,of\,that\,element\,in\,the\,compound}{Molar\,mass\,of\,the\,compound}\times 100$
Now considering data given to us in the question we can say that,
Element Sodium has percentage composition and its atomic weight is
Now calculating its relative number of atoms which is
$\dfrac{42.1}{23}=1.83$
Now its simplest ratio will be:
$\dfrac{18.9}{0.61}=3$
Now for Phosphorus its percentage composition and its atomic weight is
Now calculating its relative number of atoms which is
$\dfrac{18.9}{31}=0.61$
 Now its simplest ratio will be:
$\dfrac{0.61}{0.61}=1$
Now proceeding to oxygen its percentage composition and its atomic weight is
Now calculating its relative number of atoms which is
$\dfrac{18.9}{31}=2.44$
Now its simplest ratio will be:
$\dfrac{2.44}{0.61}=4$
 So by concluding the data simplest form of sodium, phosphorus and oxygen are and so we get our empirical formula as $N{{a}_{3}}P{{O}_{4}}$

Note:
Empirical formula is represented as the simplest whole number ratio of various atoms present in the compound as we see above and when we talk about the molecular formula so they are just the extra number of different types of atoms which are present in a molecule of a compound.