Question

1) A student prepares the synthesis by reacting 1.995g solid salicylic acid with 5.00 mL acetic anhydride (d = 1.08g/mL)

a) calculate the moles of all products and reactants remaining in the reaction mixture, assuming a 100% yield

b) acetic anhydride and water react to form acetic acid. Write a balanced equation for this

c) What is the minimum volume of water (mL) needed to convert all remaining acetic anhydride to acetic acid? (H2O d = 1.00 g/mL)

d) A student obtains, filters, rinses and dries their product to yield 2.013g acetylsalicylic acid from the conditions stated above. Calculate the percent yield of acetylsalicylic acid from the conditions stated above. Calculate the percent yield of acetylsalicylic acid formed.

Answer 1

The reaction for preperation is

a) mass of salicyclic acid = 1.995 g

molar mass of salicyclic acid = 138 g/mol

no. of moles of salicyclic acid =mass/ molar mass = 1.995 / 138 =0.01446 mol

volume of acetic anhydride = 5.00mL

density of acetic anhydride = 1.08 g/mL

so, mass of acetic anhydride = volume x density = 5.00 x 1.08 = 5.40 g

molar mass of acetic anhydride = 102 g /mol

no. of moles of acetic anhydride =mass/ molar mass = 5.4 / 102 =0.05294 mol

1 mol salicylic acid reacts with 1 mol acetic anhydride to form 1 mol acetylsalicylic acid and 1 mol acetic acid.

0.01446 mol salicylic acid reacts with 0.01446 mol acetic anhydride to form 0.01446 mol acetylsalicylic acid and 0.01446 mol acetic acid.

no. of moles of acetic anhydride left = 0.05294 - 0.01446 = 0.03848 mol.

so, at 100% yield we have  0.01446 mol acetylsalicylic acid and 0.01446 mol acetic acid and 0.03848 mol  acetic anhydride

b)

c) We are left with 0.03848 mol  acetic anhydride.

1 mol acetic anhydride requires 1 mol water.

0.03848 mol  acetic anhydride requires 0.03848 mol water.

molar mass of water = 18 g / mol

mass of water = molar mass / moles = 18 g / mol /  0.03848 mol = 467.78 g

density of water = 1.00 g/mL

volume of water = mass / density = 467.78 / 1 = 467.78 mL

d) experimental yield = 2.013 g

Theoretical yield = 0.01446 mol acetylsalicylic acid = 0.01446 x 180.16 =2.605 g acetylsalicylic acid

percentage yield = [experimental yield / theoretical yield] x 100 = [2.013 / 2.605] x 100 = 77.27 %