This question is about cycloalkenes - AQA - GCSE Chemistry - Question 6 - 2021 - Paper 2

The general formula for cycloalkenes can be deduced from the given formulas. The general formula is expressed as:

$C_nH_{2n}$

This reflects that for every 'n' carbon atoms, there are '2n' hydrogen atoms.

The displayed structural formula of C6H10Cl2 consists of the cyclohexene structure with two chlorine atoms replacing two of the hydrogen atoms. Ensure that the chlorine atoms are attached to carbon atoms within the cyclohexane ring.

To calculate the percentage by mass of chlorine in C6H10Cl2, use the formula for molar mass:

1. Calculate the molar mass of C6H10Cl2:

   • C: 6 x 12 = 72
   • H: 10 x 1 = 10
   • Cl: 2 x 35.5 = 71
   • Total = 72 + 10 + 71 = 153

2. Calculate the percentage of chlorine:

   $\text{Percentage of Cl} = \left( \frac{71}{153} \right) \times 100 \approx 46.4\%$

Thus, the percentage by mass of chlorine in C6H10Cl2 is approximately 46.4%.