Question

someone help me with these 7 questions

add a drop of iodine solution. If starch is present, I Wl iodine. The starch-iodine complex is deep blue-violet. Repeat this test with a com- mercial aspirin tablet and with the acetylsalicylic acid prepared in this experiment O N S at is the purpose of the concentrated phosphoric acid used in the first step? What would happen if the phosphoric acid were left out? 2. 1. Wh 3. If you used 250 mg of salicylic acid and excess acetic anhydride in the preceding synthesis of aspirin, what would be the theoretical yield of acetylsalicylic acid in moles? In milligrams? 4. What is the equation for the decomposition reaction that can occur with aspirin in water? 5. Most aspirin tablets contain five grains of acetylsalicylic acid. How many milligrams is this? (Hint: See the essay "Aspirin.") 6. A student performed the reaction in this experiment using a water bath at 90°C instead of 50°C. The final product was tested for the presence of phenols with ferric chloride. This test was negative (no color observed); however, the melting point of the dry product w 122-125°C. Explain these results as completely as possible. 7. If t he aspirin crystals were not completely dried before the melting point was determined, what effect would this have on the observed melting point?

Answer 1

#1: A small amount of phosphoric acid is used as catalyst in the preparation of aspirin. Phosphoric acid catalyzes the reaction by protonating acetic anhydride.

#2: If phosphoric acid is left out, the reaction would become slow.

#3: Given mass of salicylic acid (C₇H₆O₃) = 250 mg * (1 g / 1000 mg) = 0.250 g

=> Moles of salicylic acid (C₇H₆O₃) = mass/molar mass = 0.250 g / 138.121 g/mol = 0.00181 mol

The balanced chemical equation for the reaction of salicylic acid (C₇H₆O₃) and acetic anhydride (C₄H₆O₃) is

C₇H₆O₃ + C₄H₆O₃ ----> Aspirin(C₉H₈O₄) + CH₃COOH

1 mol ------ 1 mol ---------- 1 mol ----------------- 1 mol

Since 1 mole of each react to form 1 moles of each product, the mole ratio for any combination of reactant and product is 1:1.

Since acetic anhydride (C₄H₆O₃) is in excess, salicylic acid (C₇H₆O₃) is the limiting reactant.

=> Theoretical yield of Aspirin(C₉H₈O₄) = 0.00181 mol * (1/1) = 0.00181 mol (Answer)

Theoretical mass in milligram = 0.00181 mol * (180.158 g/mol) * (1000 mg / 1 g) = 326 mg (Answer)

#4: Since aspirin is an ester, it undergoes hydrolysis in water to give back salicyclic acid and acetic acid. The chemical equation is:

ÇOOH COOH OCOCH3 OH CH3COOH +H20> (Acetic acid) (Aspirin) (Salicyclic acid)