In the above reaction, 5 g of toluene is converted into benzaldehyde with 92% yield. The amount of benzaldehyde produced is ______________ × 10⁻² g. (Nearest integer)

Solution

Chemistry ma’am · 4 steps

One toluene gives one benzaldehyde, so convert grams to moles, then take 92% of the full yield.

1. Mole ratio. The -CH₃ group of toluene becomes the -CHO group. One mole of toluene (C₇H₈) gives one mole of benzaldehyde (C₇H₆O).
2. Molar masses. Toluene: 7 × 12 + 8 × 1 = 92 g mol⁻¹. Benzaldehyde: 7 × 12 + 6 × 1 + 16 = 106 g mol⁻¹.

   m_(actual) = 5/92 × 106 × 92/100 g

3. Simplify. The 92 in the molar mass cancels the 92 in the yield. That leaves (5 × 106)/100 = 5.3 g.
4. So. 5.3 g = 530 × 10⁻² g, so the answer is 530.

The common slip: 576. Leaving out the 92% yield gives the theoretical mass 5.76 g, that is 576, not 530.

The idea to keep. For yield questions, find the theoretical amount from the mole ratio first. Then multiply by the percentage yield, because the yield applies to the product, not to the reactant.

Answer from the NTA final answer key. Solution by PrepWiser.