Question

The molecular formula of Ethyne is
A. \[{C_3}{H_6}\]
B. \[{C_2}{H_4}\]
C. \[{C_2}{H_2}\]
D. \[{C_2}{H_6}\]

Answer 1

Hint: As we know, that the basics of chemistry start with the $C$ and $H$ compounds and such compounds are called as hydrocarbons and they form three type of hydrocarbons: Alkanes, Alkenes and Alkynes:
And the general formula for the Alkanes are \[{C_n}{H_{2n + 2}}\] and the general formula for alkenes are ${C_n}{H_{2n}}$ and the general formula for Alkynes are ${C_n}{H_{2n - 2}}$.



Complete step by step solution:
Alkanes are the hydrocarbons which consist of a $C - C$ single bond between them whereas Alkenes are the compound which consists of a double bond between one or more carbons and Alkynes are the compounds which consists of a triple bond between carbons and their corresponding general formulas have been discussed.
But before proceeding one must know about the nomenclature of hydrocarbons following are some rules:
i. In the names of the straight chain saturated hydrocarbons the one having a prefix of '$meth$' is referred for one carbon and the one having prefix of '$eth$' is referred for the hydrocarbon having two carbons and prop for three and but for four and so on.
ii. Double bonds in hydrocarbons are indicated by replacing the suffix $ - ane$ with $ - ene$ . Triple bonds are named similar to the alkanes and alkenes and have the suffix $ - yne$. In case of the multiple bonds present within the parent chain then its nomenclature is referred to by placing the number(s) of the first carbon of the multiple bond(s) directly in front of the base name.
Now, as we are familiar what are hydrocarbons and their nomenclature with the general formulas of hydrocarbons Let’s proceed towards the question in which we have asked the molecular formula for ethyne, The information we gather is that it is an alkyne and the general formula for an alkyne is ${C_n}{H_{2n - 2}}$ and one having prefix of ' $eth$ ' is referred for the hydrocarbon.
So, the name ethyne suggests it is a carbon compound with two carbon atoms and has a general formula ${C_n}{H_{2n - 2}}$ , so substituting $n$ with $2$ we get,
The formula of ethyne is ${C_2}{H_2}$ so the correct answer is Option C.




Note: The student should keep in mind the rules for nomenclature as well as the general formulas for hydrocarbons.