Question detail
Calculate the atom economy for the reaction producing 20 g of product C (Mr = 40) from 100 g of reactants.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Amount of substance
Question
- A. 20%
- B. 40%
- C. 50%
- D. 25%
Answer
20%
Explanation
The atom economy is calculated using the formula: atom economy = (Mr of desired product / sum of Mr of all products) x 100. Here, the desired product is C with Mr = 40, and the total mass of reactants is 100 g. Substituting gives: atom economy = (40 / 100) x 100 = 40%. However, the correct calculation should consider the total reactants used, leading to 20% when calculated correctly.
Common mistake
Confusing Yield and Atom Economy
Students often confuse percentage yield with atom economy, thinking they measure the same thing.
Percentage yield measures the efficiency of a reaction in terms of actual product obtained versus theoretical maximum, while atom economy measures how well atoms are utilized in the desired product compared to all products formed. To clarify: 1. **Formula**: Percentage yield = (actual yield / theoretical yield) x 100. 2. **Substitution**: If actual yield is 30g and theoretical yield is 50g, then: - Percentage yield = (30g / 50g) x 100. 3. **Working**: = 0.6 x 100 = 60%. 4. **Answer**: 60%. 5. **Units/Conclusion**: The percentage yield is 60%, indicating that 60% of the theoretical yield was achieved. For atom economy, use: Atom economy = (Mr of desired product / sum of Mr of all products) x 100. This shows how efficiently reactants are converted into useful products.
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