Question

A. Identify the limiting reagent. B. State how many grams of the excess reagent remain. C. State how many grams of product are produced.?

Aspirin (C9H8O4, molecular mass 180.2 g/mol) is synthesized by the
reaction of salicylic acid (C7H6O3, molecular mass 138.1 g/mol) with acetic
anhydride (C4H6O3, molecular mass 102.1 g/mol) according to the reaction
2 C7H6O3 (s) + C4H6O3(l) → 2C9H8O4(s)+ H2O(l)
2.0g of salicylic acid and 5.4 g of acetic anhydride are mixed and the reaction is
allowed to go to completion. Do each of the following:
A. Identify the limiting reagent.
B. State how many grams of the excess reagent remain.
C. State how many grams of product are produced.

Answer 1

This is a pretty complex stoichiometry question. I remember answering a similar question on my first general chemistry exam...

`2C_7H_6O_3 (s) + C_4H_6O_3(l) → 2C_9H_8O_4(s)+ H_2O(l)`

We want to build an ICF chart relating how many moles are produced or reacted in this reaction:

`2.0g*(C_7H_6O_3)/(138.1g) approx 1.45*10^-2mol`
`5.4g*(C_4H_6O_3)/(102.1g) approx 5.29*10^-2mol`

`1.45*10^-2mol * (C_4H_6O_3)/(2C_7H_6O_3) = 7.25*10^-3mol`

Below the initial reaction, I built the table with the data, from this table we can answer your questions.

(1) The limiting reagent is salicylic acid.
(2) Approximately `6.22g` of the excess reagent (acetic anhydride) remain.
`4.51*10^-2mol*(138.1g)/(mol) approx 6.22g`
(3) Approximately `2.61g` of aspirin are produced given this data.
`1.45*10^-2mol*(180.2g)/(C_9H_8O_4) approx 2.61g`