Question

The empirical formula of the compound containing 33.33% of element A (at. Wt. =10) and 66.66% of element B (at. Wt. =20) is
A.AB
B.$A_2B$
C.$AB_2$
D.$A_2B_3$

Answer 1

We can see that, we are given with the percent of an element in a compound and also, their atomic weights are also given, with the help of these we can find the empirical formula (simplest ratio of atoms present in a compound).

Complete step by step answer:
Given:
Atomic weight is element A is 10
Atomic weight is element B is 20
We can understand the meaning of empirical formula by following definition,
The empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound.
For example, we can see the empirical formula for hydrogen peroxide $\left( {{H_2}{O_2}} \right)$ is $HO$ which means one hydrogen atom for every atom of oxygen.
We can calculate the empirical formula by the following method,
We need to know the given mass, number of moles of atoms for the compound of which we are finding out empirical formula.

Element	Element A	Element B
Given mass (g)	$\dfrac{{33.33}}{{100}} = 0.3333$	$\dfrac{{66.66}}{{100}} = 0.6666$
No. of moles of atoms $\left( {n = \dfrac{m}{M}} \right)$	$\dfrac{{0.3333}}{{10}} = 0.03333$	$\dfrac{{0.6666}}{{20}} = 0.03333$
Ratio of moles(Divide by the smallest number)	$\dfrac{{0.03333}}{{0.03333}} = 1$	$\dfrac{{0.03333}}{{0.03333}} = 1$
Simplest ratio of moles	1	1

In above table,
N is no. of moles
m is given mass (It is being calculated by the percentage given of a element in a compound)
M is molar mass
As to find the ratio of moles, we need to divide the number by the smallest number to get the whole number.
From the above table, we have calculated the empirical formula of the compound.
Therefore, the correct option is A that is AB.

Note: Take care of the number you are dividing it to get the simplest ratio that number should be the nearest whole number.Atomic weight, also called relative atomic mass, ratio of the average mass of a chemical element’s atoms to some standard.