Question

An organic compound has $C$ and $H$ percentage in the ratio $6:1$ by mass and $C$ and $O$ percentage in the ratio $3:4$ by mass. The compound is:
A.$HCHO$
B.$C{H_3}OH$
C.$C{H_3}C{H_2}OH$
D.${(COOH)_2}$

Answer 1

We need to know the concept of mole ratio in order to write the formula of a compound. It is the simplest way to find the molecular formula by knowing the mole ratio of the elements constituting the compound. The given ratios will help us to find the number of moles of each constituent element which will give us the mole ratio of the compound.

Complete step by step answer:
It is given that an organic compound has a C and H percentage in the ratio $6:1$ by mass and $C$ and $O$ percentage in the ratio $3:4$3:4 by mass. Hence the ratio of $H:C:O = 1:6:8$ . We know that the atomic mass of $C$ is $12g/mol$ , that of $O$ is $16g/mol$ and that of $H$ is $1g/mol$ . To calculate the mole ratio of the compound, we need to calculate the number of moles of each element.
The number of moles of $C$= $\dfrac{{6g}}{{12g/mol}} = 0.5mol$
The number of moles of $H$=$\dfrac{{1g}}{{1g/mol}} = 1mol$
The number of moles of $O$= $\dfrac{{8g}}{{16g/mol}} = 0.5mol$
Hence the number of moles of $C$ , $H$ and $O$ are $0.5$ , $1$ and $0.5$ moles respectively. It is clear that the ratio is $1:2:1$
Therefore, the compound is $C{H_2}O$ or $HCHO$.
Hence the correct option is option (A).

Note:
It must be noted that another way to find the compound is to find the empirical formula by finding the percentage of the elements. This is calculated by calculating the percentage of each element by the total ratio which is $15$ . Converting the percentage by atomic mass will give the simplest atomic ratio and the empirical formula. Also the name of the given compound is formaldehyde.