International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

Which of the following is the molecular formula for propene?

1. C₂H₄

2. C₄H₈

3. C₃H₆

4. C₅H₁₀

The correct answer is: C₃H₆

Propene, also known as propylene, is an alkene with the chemical structure that includes a double bond between two of its carbon atoms. To determine its molecular formula, we start by identifying the number of carbon and hydrogen atoms in propene. Propene has three carbon atoms. According to the general formula for alkenes, which is CnH2n, where 'n' is the number of carbon atoms, we can substitute n with 3 (since propene has three carbon atoms) to find the corresponding number of hydrogen atoms. n = 3 leads to: Hydrogens = 2(3) = 6 This gives us the molecular formula of propene as C₃H₆, which signifies that there are 3 carbon atoms and 6 hydrogen atoms. This is consistent with the known structure of propene, which is a three-carbon chain with a double bond between the first two carbon atoms. Thus, the molecular formula for propene is C₃H₆.