A Level Chemistry OCR Practice Exam

How is atom economy calculated?

1. Sum of molecular masses of all products

2. Desired product mass divided by total mass

3. Molecular mass of the desired product multiplied by 100

4. Mass of reactants used in the reaction

The correct answer is: Molecular mass of the desired product multiplied by 100

Atom economy is a measure of the efficiency of a chemical reaction in terms of the amount of starting material that ends up in the desired product. It is calculated as the molecular mass of the desired product divided by the total molecular mass of all reactants, then multiplied by 100 to express it as a percentage. The correct choice captures this principle by focusing solely on the desired product's molecular mass and directly incorporating the factor of 100 to convert the ratio into a percentage. A higher atom economy indicates a more desirable process, as it suggests that more of the reactants have been converted into valuable products rather than byproducts. In contrast, the other options either do not accurately represent the method of calculation or fail to address the concept of 'desired product' effectively, thereby not reflecting the fundamental principles behind atom economy.