Calculations should be included in your laboratory notebook. Synthesis of Aspiri

Question

Calculations should be included in your laboratory notebook. Synthesis of Aspirin Calculate the theoretical yield and percent yield of your crude aspirin product in the calculations section of your notebook. Identify the limiting reactant. Record your results here. Review stoichiometry in Chapter 7 of the CHM-122 text/Powerpoint slides if necessary. Theoretical Yield (g) Actual Yield (g) Percent yield Limiting Reactant Recrystallization of Aspirin Describe your crude aspirin product and the recrystallized aspirin product. Note similarities and differences between the two. What properties should a solvent have to be well-suited for recrystallizing a particular compound? Record the following calculations in your notebook and include your result here. Suppose a product has the following solubilities in ethanol: 12.3 g/100mL at 78.5 degree C and 0.80g/100mL at 25 degree C Calculate the mass of recrystallized product you would expect to recover when recrystallizing of

Explanation / Answer

1. Aspirin synthesis:

C7H6O3 + C4H6O3 <===> C9H8O4 + C2H4O2

Salicylic acid Acetic unhydride Acetyl salicylic acid Acetic acid

An excess of acetic unhydride is reacted with a carefully measured amount of salicylic acid. Excess of acetic unhydride is added to ensure that all of the salicylic acid is reacted. So, salicylic acid is limiting reactant.

Given: Salicylic acid = 3.0 g

Based on the mass of salicylic acid used, calculate theoretical yield and percent yield.

First calculate the moles of salicylic acid

moles of salicylic acid = 3.0g * 1mol/138.12g = 0.0217 mol

Since, the molar ratio of salicylic acid to acetyl salicylic acid(aspirin) in the balanced equation is 1:1

moles of aspirin = 0.0217 mol

therefore, 0.0217 mol aspirin*180.17g aspirin/1mol aspirin = 3.91 g (theoretical yield)

Experimental (actual) yield = 3.11 g

%yield = experimental yield/theoretical yield *100 = 3.11g/3.91g*100 = 79.5%

2. Recrystallization of Aspirin

When an organic compound is produced, it needs to be purified. This is because most organic reactions produce by-products. This purification is done by recrystallization. The crude product may contain impurities which are slightly insoluble in solvent or may readily dissolve in the solvent. One simple way to tell whether an organic compound is pure, is to measure its melting or boiling point. A pure compound melts sharply. If it contains impurities, then it will melt slowly. Impure compound shows lower melting point than that of pure compound.

3. To be well suited for recrystallizing a particular compound, a solvent should have following properties:

4. Given: product solubilities in ethanol = 12.3g/100mL at 78.50C and 0.80g/100mL at 250C

First calculate the percent solid lost (at 250C) = solubility at 250C / solubility at 78.50C * 100

= 0.80g/12.3g *100 = 6.5%

now, calculate the grams of solid lost = mass of crude product * percent lost = 14.5g*6.5/100 = 0.9425 g

grams of recrystallized product recovered = grams of crude product - grams of solid lost

= 14.5 g - 0.9425 g = 13.56 g

% recovery = grams recovered / grams crude product *100 = 13.56 g/14.5 g * 100 = 93.5 %

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