What is the limiting reagent?
2018-02-22 12:33 am
Assume that 5.0 g of salicylic acid and 4.5 mL of acetic anhydride (density ρ = 1.08 g mL-1) are used in the preparation of aspirin. What is the limiting reagent? Justify your answer.
回答 (1)
2018-02-22 12:53 am
Molar mass of salicylic acid (C₇H₆O₃) = (12.0×7 + 1.0×6 + 16.0×3) g mol⁻¹ = 138.0 g mol⁻¹
Molar mass of acetic anhydride (C₄H₆O₃) = (12.0×4 + 1.0×6 + 16.0×3) g mol⁻¹ = 102.0 g mol⁻¹
Initial number of moles of salicylic acid = (5.0 g) × (1 mol / 138.0 g) = 0.0362 mol
Initial number of moles of acetic anhydride = (4.5 mL) × (1.08 g / mL) × (1 mol / 102.0 g) = 0.0476 mol
Balanced equation for the reaction:
C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + C₂H₄O₂
Mole ratio C₇H₆O₃ : C₄H₆O₃ = 1 : 1
(Initial number of moles of salicylic acid) < (Initial number of moles of acetic anhydride)
Hence, salicylic acid is the limiting reagent.
Molar mass of acetic anhydride (C₄H₆O₃) = (12.0×4 + 1.0×6 + 16.0×3) g mol⁻¹ = 102.0 g mol⁻¹
Initial number of moles of salicylic acid = (5.0 g) × (1 mol / 138.0 g) = 0.0362 mol
Initial number of moles of acetic anhydride = (4.5 mL) × (1.08 g / mL) × (1 mol / 102.0 g) = 0.0476 mol
Balanced equation for the reaction:
C₇H₆O₃ + C₄H₆O₃ → C₉H₈O₄ + C₂H₄O₂
Mole ratio C₇H₆O₃ : C₄H₆O₃ = 1 : 1
(Initial number of moles of salicylic acid) < (Initial number of moles of acetic anhydride)
Hence, salicylic acid is the limiting reagent.
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