Question

Mass of salicylic acid and weighing boat (g) 2.753

Mass of weighing boat after transfer (g) 0.7340
Mass of empty 100 mL beaker (g) 50.572
Mass of dried product in 100 mL beaker (g) 52.599

In your preparation of ASA, the ethanoic anhydride used in the reaction was in excess. Using your mass of salicylic acid and the balanced equation for the reaction; show that the ethanoic anhydride was, indeed, in excess. Note: the density of ethanoic anhydride is 1.092g/mL.

Answer 1

The calculation shows that 0.01993 mol of salicylic acid was used in the ASA synthesis. Since the reaction requires an equimolar amount of ethanoic anhydride, and it was provided in excess, we conclude that ethanoic anhydride was indeed in excess.

Step-by-step explanation:

To determine if ethanoic anhydride was in excess during the preparation of acetylsalicylic acid (ASA) from salicylic acid, we need to calculate the moles of salicylic acid initially present and compare it to the stoichiometric requirements of the reaction with ethanoic anhydride.

The balanced chemical equation for the synthesis of ASA is:

C7H6O3 + (CH3CO)2O → C9H8O4 + CH3COOH

We need to know the molar mass of salicylic acid (C7H6O3) to find the moles present:

• Molar mass C7H6O3: 138.12 g/mol

Given the mass of salicylic acid is 2.753 g, the moles of salicylic acid are:

0.01993 mol = 2.753 g / 138.12 g/mol

Since the reaction is 1:1, it would require 0.01993 mol of ethanoic anhydride. Using the density of ethanoic anhydride (1.092 g/mL), we can show that the volume required for stoichiometric amounts is:

Volume = Moles × Molar mass / Density

We do not have the exact number of mL used during the experiment, but since the ethanoic anhydride was in excess, it means that more was provided than the calculated volume needed. This assures that all of the salicylic acid reacts, and the excess reactant – ethanoic anhydride – does not limit the production of ASA.