Concept explainers
Aspirin or acetylsalicylic acid is synthesized by combining salicylic acid with acetic anhydride:
(a) How much salicylic acid is required to produce 0.400 g of aspirin (about the content in a tablet), assuming acetic anhydride is present in excess? (b) Calculate the amount of salicylic acid needed if only 74.9 percent of salicylic is converted to aspirin. (c) In one experiment. 9.26 g of salicylic acid reacts with 8.54 g of acetic anhydride. Calculate the theoretical yield of aspirin and the percent yield if only 10.9 g of aspirin is produced.

Interpretation:
The amount of salicylic acid at the given conditions, the theoretical yield, and the percent yield of aspirin in the reaction are to be calculated.
Concept introduction:
Atomic mass of elements is measured in terms of atomic mass unit. One atomic mass unit is defined as the number of elementary particles present in
The number of moles are given by the following expression:
The percent yield of the compound is given by the following expression:
The mass of compound can be calculated as
Here,
The mass of salicylic acid is given by the expression:
Answer to Problem 146AP
Solution:
(a)
(b)
(c)
Explanation of Solution
a) The number of salicylic acid is required to produce 0.400 g of aspirin.
The number of moles is given by the following expression:
Since molar ratio of salicylic acid to aspirin is
The above expression can be rewritten as
So, the mass of salicylic acid is given by the following expression:
The above expression can be rewritten as
Substitute
Hence, the mass of salicylic acid is
b) The amount of salicylic acid needed if only 74.9% of salicylic acid is converted to aspirin.
The amount of salicylic acid used was
Since 74.9% of salicylic acid is converted to aspirin, the molar ratio of aspirin to that of salicylic acid is
The amount salicylic acid used is calculated as
Hence, mass of salicylic acid required is
c)The theoretical yield of aspirin and the percent yield if only 10.9 g of aspirin is produced.
Mass of salicylic acid
Mass of acetic anhydride
Mass of aspirin
Since the molar ratio of salicylic acid to aspirin is
The number of moles of salicylic acidis given by the following expression:
Substitute
Since molar ratio of acetic anhydride to aspirin is also
The number of moles of acetic anhydrideis given by the following expression:
Substitute
Therefore, it is clear that salicylic acid is a limiting reactant. So, mass of aspirin produced is calculated as
Substitute
Therefore, theoretical yield or actual yield is
The percent yield of the aspirin is given by the following expression:
Percent yield is given by =
Substitute
Hence, the theoretical yield should be
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