Question 1

Which of the following best describes the role of sulfuric acid ($$\mathrm{H_2SO_4}) in $$the synthesis of aspirin from salicylic acid and acetic anhydride?

Accepted Answer

It acts as a catalyst by protonating the acetic anhydride, increasing its electrophilicity.

Question 2

During the recrystallization of crude aspirin, why is ethanol used as the solvent?

Accepted Answer

Aspirin is soluble in hot ethanol but insoluble in cold ethanol, allowing for purification by crystallization.

Question 3

Which equation correctly represents the balanced chemical reaction for the synthesis of aspirin?

Accepted Answer

$$\mathrm{C_7H_6O_3} + \mathrm{C_4H_6O_3} \rightarrow \mathrm{C_9H_8O_4} + \mathrm{C_2H_4O_2}$$

Question 4

A student obtained 3.0 g of aspirin from 2.4 g of salicylic acid (molar mass = 138 g/mol). What is the theoretical yield of aspirin (molar mass = 180 g/mol), and what is the percent yield?

Accepted Answer

Theoretical yield = 3.13 g; Percent yield = 95.8%

Question 5

In the ferric chloride test, a purple coloration indicates the presence of which functional group?

Accepted Answer

Phenol group ($$-\mathrm{OH}$$ attached to an aromatic ring)

Question 6

Why is it important to add water to the reaction mixture after heating during the synthesis of aspirin?

Accepted Answer

To hydrolyze any unreacted acetic anhydride and precipitate the aspirin product.

Question 7

Which of the following statements best explains why vacuum filtration is used after the synthesis of aspirin?

Accepted Answer

Vacuum filtration rapidly separates the solid aspirin from the liquid reaction mixture.

Question 8

During thin-layer chromatography (TLC) analysis, what does a higher $$R_f$$ value indicate about a compound?

Accepted Answer

The compound is less polar and travels further up the plate with the mobile phase.

Question 9

If the ferric chloride test on your synthesized aspirin gives a purple color, what does this suggest about the purity of your product?

Accepted Answer

The product contains unreacted salicylic acid, indicating incomplete reaction or poor purification.

Question 10

Which property of a good recrystallization solvent is most important for purifying aspirin?

Accepted Answer

The solvent should dissolve aspirin when hot but not when cold.

Question 11

What is the main reason for cooling the reaction mixture in an ice bath after synthesis but before filtration?

Accepted Answer

To maximize the precipitation of aspirin by decreasing its solubility.

Question 12

Which of the following is a potential hazard when handling acetic anhydride in the laboratory?

Accepted Answer

It causes burns upon contact and is a strong lachrymator.

Question 13

A student uses 2.4 g of salicylic acid ($$\mathrm{C_7H_6O_3}$$, molar mass = 138 g/mol) and 6.0 mL of acetic anhydride ($$\mathrm{C_4H_6O_3}$$, density = 1.08 g/mL, molar mass = 102 g/mol). Which is the limiting reagent?

Accepted Answer

Salicylic acid

Question 14

Which of the following best explains why the ferric chloride test is used to assess the purity of synthesized aspirin?

Accepted Answer

Ferric chloride reacts with unreacted phenolic groups, indicating the presence of salicylic acid impurity.

Question 15

Which of the following is NOT a step in the recrystallization of aspirin?

Accepted Answer

Adding concentrated sulfuric acid to the cold solution.

Question 16

If a TLC plate shows two spots for a sample of synthesized aspirin, what does this indicate?

Accepted Answer

The sample contains both aspirin and an impurity, such as unreacted salicylic acid.

Question 17

Which of the following is the main advantage of using acetic anhydride over acetic acid in the synthesis of aspirin?

Accepted Answer

Acetic anhydride reacts more completely with salicylic acid, increasing yield.

Question 18

Which of the following best describes the purpose of refluxing the reaction mixture during the synthesis of aspirin?

Accepted Answer

To maintain the reaction at a constant temperature and prevent loss of volatile components.

Question 19

Which of the following is a correct calculation for the percent yield of aspirin if 2.0 g is obtained and the theoretical yield is 2.5 g?

Accepted Answer

$$	ext{Percent yield} = \frac{2.0}{2.5} 	imes 100\% = 80\%$$

Act. 2: Synthesis and Purification of Aspirin

Guida di studio - Domande di pratica

Study guide - Flashcard