1) what is the % yield of the crude and the recrystallized aspirin ? 2) Should t
ID: 582063 • Letter: 1
Question
1) what is the % yield of the crude and the recrystallized aspirin ? 2) Should the melting point of the recrystallized aspirin be higher or lower than that of the crude aspirin ? Resnlts: Resnlts 1.0g 0.2152 2.5ml 2-3 drops 1.0021g Description Salicylic acicd Acetic Anhydride H3Po4 Crude Weight Crude Melting Point 130 C Part 2 Recrystallization Actual aspirin recommends Group aspirin weighted Filter Paper Ethanol Weight of recrystallized aspirin Melting Point of recrystallized aspirin 250mg 0.3804g 0.2227 0.75ml 0.2416 135 CExplanation / Answer
In the above reaction equation, Salicylic acid and acetic anhydride reacts in 1:1 ratio.
Now,
Molar mass of salicylic acid = 138 g/mol
So, 138 g of salicylic acid = 1 mol
or 1 g of salicylic acid = (1/138) mol = 0.007 mol
Volume of acetic anhydride = 2.5 mL
Density of acetic anhydride = 1.08 g/mL
So, mass of acetic anhydride = 2.5 mL x 1.08 g/mL = 2.7 g
Molar mass of acetic anhydride = 102 g/mol
So, 102 g of of acetic anhydride = 1 mol
or 1 g of of acetic anhydride = (1/102) mol
or 2.7 g of of acetic anhydride = (2.7/102) mol = 0.0264 mol
Since acetic anhydride is taken in excess, so, salicylic acid is the limiting reagent.
So, 0.007 mol of salicylic acid will produce 0.007 mol of aspirin.
Molar mass of aspirin = 165 g/mol
So, 1 mole of aspirin = 165 g
or 0.007 mol of aspirin = 0.007 x 165 g = 1.16 g (Theoritical yield)
Weight of recrystallized aspirin = 0.2416 g (Actual yield)
So, % Yield = (Actual yield / Theoritical yield) x 100
= (0.2416 / 1.16) x 100
= 20.83 %
2.
A substance (solid) containing soluble impurities usually melts at a lower temperature than the pure compound. Hence, the melting point of the recrystallized aspirin be higher than that of the crude aspirin.
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