1. Calculate the molar masses of salicylic acid, acetic anhydride and ASA. 2. Ca

Question

1. Calculate the molar masses of salicylic acid, acetic anhydride and ASA.

2. Calculate the number of moles of salicylic acid and acetic anhydride used in the experiment.

3. Identify the limiting reagent in your reaction (Recall: the limiting reagent is the one with the smaller number of moles, since the reaction required equimolar amounts of the two reactants).

4. Using the limiting reagent’s moles, give the number of moles of ASA expected, if the reaction gave 100% yield

5. Calculate the moles of ASA actually obtained from the grams of product in your reaction.

6. Calculate the % yield

7. Calculate the % error in your melting point, compared to the accepted one.

Weight of salicylic acid 2.1g_ Volume of Acetic Anhydride added Buret reading initial Total volume 16.2ml_- Buret reading final 21.2ml 5.00ml Drop, phosphoric acid added-5 drop Weight of watchglass + filter paper Weight ofwatchgass+ filter + aspirin-_ 60.7g- Melting point of aspirinStart from 120c up to 134c 54.22g ? ? . ABC

Explanation / Answer

Answering (1)

Molar mass of Salicylic acid = C7H6O3 = 12 x 7 + 1 x 6 + 16 x 3 = 138 g/mol

Molar mass of Acetic anhydride = C4H6O3 = 12 x 4 + 1 x 6 + 16 x 3 = 102 g/mol

Molar mass of ASA = Acetylsalicylic acid = C9H8O4 = 12 x 9 + 1 x 8 + 16 x 4 = 180 g/mol

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Answering (2)

Moles of salicylic acid = (quantity in gram/molar mass) = (2.1 g)/(138 g/mol) = 0.015 mol

Density of acetic anhydride = 1.082 g/mL

Acetic anhydride used = 5.00 mL = 5.00 mL x 1.082 g/mL = 5.41 g

Therefore, the moles of acetic anhydride used = (5.41 g)/(102 g/mol) = 0.053 mol

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Answering (3)

Moles of salicylic acid < moles of acetic anhydride

Therefore the limiting reagent in the reaction is salicylic acid.

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Answering (4)

Theoretically, 1 mol of salicylic should produce 1 mol of ASA or aspirin for 100 % yield

Therefore, 0.015 mol should produce 0.015 mol = (0.015 mol) x (180 g/mol) = 2.7 g ASA or aspirin for 100 % yield.

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For 4 and 5 : Please check the data you provided. Is it really = 560.7 g?

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