Question

On analysis, a certain compound was found to contain iodine and oxygen in the ratio of 254:80. The formula of the compound is:
[Atomic mass: I = 127, O =16]
A. IO
B. ${I_2}O$
C. ${I_5}{O_2}$
D. ${I_2}{O_5}$

Answer 1

To derive the molecular formula of the compound we first need to find out the mole ratio of the atoms which combine to form the compound by dividing the mass of the atom with its atomic mass.

Complete step by step answer:
Given,
The iodine and oxygen is present in the ratio of 254:80.
The atomic mass of iodine (I) is 127.
The atomic mass of oxygen (O) is 16.
The mass of iodine is 254 g.
The mass of oxygen is 80 g.
To determine the formula, first we need to find out the moles of the elements given as mass and atomic mass is given.
The formula for calculating the number of moles is shown below.
$n = \dfrac{m}{M}$
Where,
n is the number of moles.
m is the given mass
M is the atomic mass
To calculate the number of moles of iodine(I), substitute the values of mass and atomic mass in the above equation.
$\Rightarrow n = \dfrac{{254g}}{{127g/mol}}$
$\Rightarrow n = 2mol$
To calculate the number of moles of oxygen (O), substitute the values of mass and atomic mass in the above equation.
$\Rightarrow n = \dfrac{{80g}}{{16g/mol}}$
$\Rightarrow n = 5mol$
Thus, the mole ratio of iodine and oxygen is 2:5.
The resulting formula of the compound is ${I_2}{O_5}$.

So, the correct answer is Option D.

Note: Generally in deriving the molecular formula, if the moles are obtained in decimal terms then the moles is divided with the smallest value of moles to find out the simplest whole number ratio.