The relative density of vapors of alkyne for helium is 13.5. Determine the alkyne formula.

The relative density of vapors of alkyne for helium is 13.5. Determine the alkyne formula. Draw up the structural formula of one of its isomers.

Let’s implement the solution:
Let’s write down the data on the condition of the problem:
1. Given: CxNu – hydrocarbon, alkyne;
D (He) = 13.5;
M (He) = 4 g / mol;
Determine: molecular formula.
2. Let’s calculate the molar mass:
M (CxHy) = D (He) * M (He) = 13.5 * 4 = 54 g / mol.
3. Let us establish the formula based on the common for alkynes:
CnH2n – 2 = 54;
12n + 2 – 2 = 54;
12n = 54;
n = 4.5;
C4H6;
Checking: M (C4H6) = 12 * 4 + 6 = 54 g / mol;
HC (triple bond) C – CH2 – CH3 – butyne.
4. Isomer of butyne:
Н3С – С (triple bond) С – СН3 – butyne – 2.
Answer: C3H4 is a representative of the butyn alkynes class.