I need some help with calculating percent yield and percent purity of aspirin.
Here's my data (questions follow):
SYNTHESIS
Mass of salicylic acid.., 2.0 g
Volume of acetic anhydride.., 5 mL
Mass of watch glass.., 22.10 g
Mass of aspirin and watch glass.., 28.01 g
Mass of aspirin.., 5.91 g
DETERMINATION OF PURITY
Mass of aspirin.., 0.34 g
Concentration of NaOH.., 0.1 M
Initial buret reading.., 0 mL
Final buret reading.., 15.8 mL
Volume of NaOH used.., 15.8 mL
Number of moles of NaOH required.., 1.60 x10^-3 mol
1. Calculate your mass percent yield of aspirin.
(actual yield, g/theoretical yield, g) x 100
Not sure what numbers I'd use here...
2. Calculate the percent purity of your aspirin.
(mass of aspirin, g (titration)/mass of aspirin, g (synthesis)) x 100
(0.34 g/5.91 g) x 100 = 5.8%
I'm pretty sure that's right, but not completely.
patience. Answered below on the original post.
I need help with this What mass of bleach (NaCLO; 74.44g/mol) could be made from 72.0 g of NaOH and 72.0 g Cl2 at 95.0 % yield
To calculate the percent yield of aspirin, you need to compare the actual yield (mass of aspirin obtained) to the theoretical yield (mass of aspirin expected based on stoichiometry). The theoretical yield can be calculated using the stoichiometry of the reaction.
In this case, the synthesis equation for aspirin is:
C7H6O3 + C4H6O3 -> C9H8O4 + C2H4O2
1 mole of salicylic acid (C7H6O3) reacts with 1 mole of acetic anhydride (C4H6O3) to produce 1 mole of aspirin (C9H8O4) and 1 mole of acetic acid (C2H4O2).
To determine the number of moles of salicylic acid used, you divide its mass by its molar mass.
Number of moles of salicylic acid = Mass of salicylic acid (2.0 g) / Molar mass of salicylic acid (138.12 g/mol)
Similarly, to determine the number of moles of acetic anhydride used, you divide its volume by its molar volume.
Number of moles of acetic anhydride = Volume of acetic anhydride (5 mL) / Molar volume of acetic anhydride
You can then use the stoichiometry to determine the theoretical yield of aspirin, which is the number of moles of aspirin obtained.
Theoretical yield of aspirin = Number of moles of salicylic acid (from above) x (Molar mass of aspirin / Molar mass of salicylic acid)
Finally, you can calculate the percent yield of aspirin using the formula:
Percent yield = (Actual yield of aspirin (5.91 g) / Theoretical yield of aspirin) x 100
For the percent purity of the aspirin, you need to compare the mass of the aspirin obtained in the titration to the mass of the aspirin obtained in the synthesis.
Using the formula:
Percent purity = (Mass of aspirin obtained in the titration / Mass of aspirin obtained in the synthesis) x 100
In your calculation, you correctly used the formula to calculate the percent purity of the aspirin:
(0.34g / 5.91g) x 100 = 5.8%
So, your calculation for the percent purity is correct. However, to calculate the percent yield, you need to use the values mentioned above and plug them into the formula:
(Actual yield of aspirin (5.91 g) / Theoretical yield of aspirin) x 100