Michael Faraday weighs out 3.12 g. of salicylic acid in a 100 mL flask and adds

Question

Michael Faraday weighs out 3.12 g. of salicylic acid in a 100 mL flask and adds 1.89 mL of acetic anhydride (density - 1.080 g'mL). Determine the maximum (theoretical) number of grams of acetylsalicylic acid he can prepare. If Mr. Faraday obtained 3.38 g. of Aspirin, calculate the % yield. Briefly, explain why he might have obtained this amount of product. At 20 degreeC, the solubility of salicylic acid is 0.20 g/100 mL. Calculate the molar concentration of salicylic acid in solution at this temperature. What density assumption can help you in solving this problem?

Explanation / Answer

Mass of salicylic acid = 3.12 g

Molar mass of salicylic acid = 138.12 g/mol

Moles of acid = 3.12 /138.12 =0.0226 mol

Mass of acetic anhydride = volume x density

= 1.89 mL x 1.080 g/mL

= 2.04 g

Moles of acetic anhydride = 2.04 g /102.09

= 0.020 moles

1 mole salicylic acid reacts with 1 mole acetic anhydride to give 1mole of acetyl salicylic acid

Here acetic anhydride is present less than salicylic acid moles

So acetic anhydride is limiting reagent

Moles of acetylsalicyclic anhydride= 0.020 moles

Mass of acetyl salicylic anhydride is 0.020 moles x 180.16 g/mol == 3.6032 grams

percentage yield =( 3.38 g /3.6032 g ) x 100

= 93.8 %

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