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

Which compound is used to represent the repeat unit of poly(propene)?

1. CH2=CH2

2. CH3-CH=CH2

3. Cl-CH2-CH

4. C2H4

The correct answer is: CH3-CH=CH2

The repeat unit of poly(propene) is derived from the monomer propene, which has the chemical structure CH2=CH-CH3. When propene polymerizes, it forms long chains of interconnected repeat units. The correct representation of the repeat unit in poly(propene) involves the formula that captures this arrangement. In this case, option B, CH3-CH=CH2, represents the structure of propene with the double bond indicated, although slightly rearranged. During polymerization, the double bond in propene opens up, allowing the molecules to link together, ultimately forming the polymer. This choice accurately reflects the nature of propene as the basis for poly(propene). The other options do not represent the correct structure of propene or its repeat unit in poly(propene). For example, option A refers to ethene, not propene; option C suggests a chlorinated compound that does not correlate with the structure of propene and is not representative of poly(propene); and option D, while being ethylene (a simple alkene), does not pertain to the structure of poly(propene) as it lacks the necessary carbon chain length and branching. Thus, option B is the most fitting representation of the repeat