Aspirin or acetyl salicylic acid is synthesized by reacting...

Aspirin or acetyl salicylic acid is synthesized by reacting salicylic acid with aceticanhydride:$$\mathrm{C}_{7}\mathrm{H}_{6}\mathrm{O}_{3}+\mathrm{C}_{4} \mathrm{H}_{6} \mathrm{O}_{3} \quad \longrightarrow \mathrm{C}_{9} \mathrm{H}_{8}\mathrm{O}_{4}+\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}$$ (a) How much salicylic acid is required to produce $0.400 \mathrm{~g}$ 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 acid is converted to aspirin. (c) In one experiment, $9.26 \mathrm{~g}$ of salicylic acid is reacted with $8.54 \mathrm{~g}$ of acetic anhydride. Calculate the theoretical yield of aspirin and the percent yield if only $10.9 \mathrm{~g}$ of aspirin is produced.

Aspirin or acetyl salicylic acid is synthesized by reacting salicylic acid with aceticanhydride:$$\mathrm{C}_{7}\mathrm{H}_{6}\mathrm{O}_{3}+\mathrm{C}_{4} \mathrm{H}_{6} \mathrm{O}_{3} \quad \longrightarrow \mathrm{C}_{9} \mathrm{H}_{8}\mathrm{O}_{4}+\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}$$
(a) How much salicylic acid is required to produce $0.400 \mathrm{~g}$ 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 acid is converted to aspirin.
(c) In one experiment, $9.26 \mathrm{~g}$ of salicylic acid is reacted with $8.54 \mathrm{~g}$ of acetic anhydride. Calculate the theoretical yield of aspirin and the percent yield if only $10.9 \mathrm{~g}$ of aspirin is produced.

Key Concepts

Percent Yield

Percent yield is the ratio of the actual yield (the amount of product actually obtained) to the theoretical yield, multiplied by 100. It provides an indication of the efficiency of the reaction and factors in experimental losses, side reactions, or incomplete reactions.

Reaction Efficiency and Conversion

Reaction efficiency and conversion percentages reflect the extent to which the reactants are converted into products in a chemical reaction. These concepts are important when the reaction does not go to completion, necessitating adjustments in stoichiometric calculations to account for partial conversion of reactants.

Theoretical Yield

The theoretical yield is the maximum quantity of product that can be generated from a given amount of reactants, based solely on the stoichiometric predictions from the balanced chemical equation. It assumes that the reaction proceeds to completion with no deviations.

Limiting Reagent

The limiting reagent is the reactant that is completely consumed in a reaction, thereby determining the maximum amount of product that can be formed. Identifying the limiting reagent is critical when reactants are not present in stoichiometrically equivalent amounts.

Molar Mass

Molar mass is the mass of one mole of a substance and is used to convert between mass (in grams) and amount (in moles). In stoichiometric calculations, determining the molar mass of each reactant and product is essential for accurate computation of the amounts involved in the reaction.

Stoichiometry

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. It requires using the balanced chemical equation to convert masses to moles and applying mole ratios to determine how much of one substance is needed to react with or produce a given amount of another substance.

Transcript

00:01 Okay, so this is a stoichiometry problem.

00:04 We have our balance equation given to us.

00:06 I've written the names of these components just to help us out, and i've also written their molar masses.

00:14 Okay, so let's start with part a.

00:16 Part a tells us that we are starting with 0 .4 grams of aspirin.

00:25 And so what we can do is we can convert from grams of aspirin to moles of aspirin using the molar mass, so 180.

00:33 Then we can say, using our balanced equation for every one mole of aspirin, there is one mole of salicylic acid, which is what the question is asking us about.

00:47 And then we can convert from moles of salicylic acid to grams of salicylic acid using the molar mass, which here is 138 .12.

00:59 So we multiply across the top, divide by our bottom numbers, and this gives us a final answer of 0 .307 grams of salicylic acid.

01:12 That is our answer to part a.

01:17 Okay, part b tells us that 74 .9 % is used.

01:26 So that is the percent yield.

01:28 Percent yield is equal to actual divided by theoretical.

01:34 And so that number that we just found in part a, that is our theoretical value.

01:40 So what we're saying is 0 .307 grams should be formed theoretically.

01:46 Part b tells us, well, 74 .9 % of that was formed.

01:50 So we're going to solve for x.

01:53 So x is equal to, well, we'd change it right to a decimal.

01:57 0 .749 times 0 .307, which gives us 0 .230 grams of salicylic acid.

02:14 That would be our answer to part b.

02:18 Okay, part c, slightly different here.

02:22 This is also a limiting reactant problem because in part a and b, we were told that salicylic acid, was the limiting and acetic anhydr was the excess.

02:35 But here it actually gives us starting information about both.

02:39 So when we're working that type of problem, we want to set up two different stoichiometry problems to identify the limiting reactants.

02:47 So we're going to have one for salicylic acid and one for acetic inhydrate...

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