Question

Two elements X (atomic mass = 75) and Y (atomic mass = 16) combine to give a compound having 75.8% of X. The formula of the compound is:
A. ${X_2}{Y_2}$
B. ${X_2}Y$
C. ${X_2}{Y_3}$
D. $XY$

Answer 1

To solve this question, we will use the method of finding the empirical formula of a compound. The simplest whole number ratio of different atoms present in a compound is the empirical formula.

Complete step by step answer:
There are two elements in the compound, X and Y.
Atomic mass of X = 75.
Atomic mass of Y = 16.
Percentage of X = 75.8 %
Percentage of Y = (100 – 75.8) % = 24.2 %.
Now, we will calculate the empirical formula of this compound.

Element	Percentage of element	Atomic mass of element	Relative number of atoms = $\dfrac{{{\text{Percentage}}}}{{{\text{Atomic mass}}}}$	Simplest atom ratio	Simplest whole number atom ratio
X	75.8	75	$\dfrac{{75.8}}{{75}} = 1.01$	$\dfrac{{1.01}}{{1.01}} = 1$	$1 \times 2 = 2$
Y	24.2	16	$\dfrac{{24.2}}{{16}} = 1.51$	$\dfrac{{1.51}}{{1.01}} = 1.5$	$1.5 \times 2 = 3$

From the above table, we can see that the simplest whole number atom ratio of X is 2 and Y is 3.
Hence, the empirical formula of the given compound will be, ${X_2}{Y_3}$
So, the correct answer is “Option C”.

Note: With the help of empirical formula, the molecular formula of a compound can also be identified. The molecular formula displays the exact number of different types of atom forms present in a molecule of a compound. First, we have to find out the empirical formula and then we will calculate the empirical formula mass. Then we determine the value of n by, $n = \dfrac{{{\text{molecular mass}}}}{{{\text{empirical formula mass}}}}$. After that, multiply the empirical formula by n to get the molecular formula, molecular formula = n$\times$empirical formula.