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 positive.
I'm not sure either but here is some discussion.
From synthesis:
Convert mass salicylic acid to mols.
Convert mols salicylic acid to mols aspirin know that 1 mol salicylic acid should produce 1 mol aspirin.
Convert mols aspirin to grams aspirin from mols aspirin x molar mass aspirin = g aspirin theoretical yield.
According to my calculations, 2.0 g salicylic acid should produce about 2.6 g aspirin. According to your data, you produced 5.91 g and that is WAY over what you should have obtained. Perhaps you didn't dry the aspirin on the watch glass very well before weighing.
If all of the synthesis part is as I understand it, then actual yield is 5.91 (I GUESS we are assuming all of that is aspirin) and theoretical yield is 2.61 and that makes for greater than 200% yield.
For #2, the answer is more straight forward. The only complaint I have here is that the 0.34g is labeled as mass aspirin when in reality it is the mass of the SAMPLE. From below you see mass of aspirin in that sample is less than that).
mols NaOH = M x L = 0.1 x 0.00158 = ??
mols aspirin = the same number.
multiply mols aspirin x molar mass aspirin to obtain grams aspirin. I found 0.284 g (that's out of the 0.34 g sample taken for analysis). That divided by 0.34 (that is the mass of sample taken for analysis) x 100 = %purity and I found about 84% purity. Of course the immediate question is, "What is rest of it?" Since you have over 200% yield, then we might expect SOME of the sample to be impure aspirin BUT there is a discrepancy even in these numbers for 84% yield means you have an extra 16% something else there but the theoretical yield is so much MORE than that. There is another 185% somewhere.
I suspect the original sample was not dried thoroughly AND I suspect that some time elapsed between the preparation of the sample and the determination of purity which gave it some time to air dry more.I hope this gets you started.
Mass percent yield is found first by getting your experimental yield in grams by multiplying grams of SA sample used, times the molar mass of SA, times the mole ratio of SA and aspirin, times the molar mass of aspirin. Then divide the experimental (actual) yield by the theoretical yield, then multiply by 100 to get the mass percent yield.
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To calculate the mass percent yield of aspirin, you need to determine the actual yield and the theoretical yield. The actual yield is the mass of aspirin obtained during the synthesis process, which in this case is 5.91 grams. The theoretical yield is the maximum amount of aspirin that could have been produced, calculated using stoichiometry (mole ratios) and the molar masses of the reactants and products.
To determine the theoretical yield, you first need to convert the mass of salicylic acid to moles. Use the molar mass of salicylic acid (should be given in grams/mole) to calculate the number of moles. Next, use the stoichiometric ratio from the balanced chemical equation (assuming it is given) to determine the number of moles of aspirin that should have formed. Finally, convert the moles of aspirin to grams using the molar mass of aspirin.
Once you have calculated the theoretical yield, use the formula:
Mass percent yield = (actual yield / theoretical yield) x 100
So, substituting the values in the formula:
Mass percent yield = (5.91 g / theoretical yield) x 100
Note that you need to calculate the theoretical yield using the steps described above before substituting the value into the formula to get the final answer.
For the second question regarding the percent purity of the aspirin, you already have the mass of aspirin used in the titration, which is 0.34 grams. Divide this by the mass of aspirin obtained during the synthesis process (5.91 grams) and multiply by 100 to get the percent purity:
Percent purity = (0.34 g / 5.91 g) x 100
This will give you the percentage of the sample that is pure aspirin. Keep in mind that the purity may not be 100% due to impurities or incomplete reactions during the synthesis process.
To summarize:
1. Calculate the theoretical yield of aspirin using stoichiometry and molar masses.
2. Substitute the actual yield into the formula to calculate the mass percent yield.
3. Divide the mass of aspirin used in the titration by the mass of aspirin obtained during synthesis and multiply by 100 to get the percent purity.
To calculate the mass percent yield of aspirin, follow these steps:
1. Convert the mass of salicylic acid used to moles by dividing the mass by the molar mass of salicylic acid (138.12 g/mol).
Moles of salicylic acid = 2.0 g / 138.12 g/mol = 0.0145 mol
2. Calculate the theoretical yield of aspirin based on the moles of salicylic acid used. Since the reaction proceeds in a 1:1 ratio, the moles of aspirin will be the same as the moles of salicylic acid.
The molar mass of aspirin is 180.16 g/mol.
Theoretical yield of aspirin = 0.0145 mol x 180.16 g/mol = 2.62 g
3. Calculate the mass percent yield by dividing the actual yield (5.91 g) by the theoretical yield (2.62 g) and multiplying by 100.
Mass percent yield = (5.91 g / 2.62 g) x 100 = 225.2%
Note: A mass percent yield greater than 100% indicates that there may be errors in the experimental procedure, such as incomplete drying or loss during transfer.
Now let's move on to calculating the percent purity of the aspirin using the data from the titration:
1. Convert the volume of NaOH used to moles using the molarity of NaOH:
Moles of NaOH = 0.1 M x 0.0158 L = 0.00158 mol
2. Since the reaction between NaOH and aspirin is 1:1, the moles of aspirin will be the same as the moles of NaOH.
3. Calculate the mass of aspirin in the sample used for titration:
Mass of aspirin = moles of aspirin x molar mass of aspirin = 0.00158 mol x 180.16 g/mol = 0.284 g
4. Calculate the percent purity by dividing the mass of aspirin obtained from the titration (0.284 g) by the mass of aspirin from the synthesis (5.91 g) and multiplying by 100.
Percent purity = (0.284 g / 5.91 g) x 100 = 4.81%
Note: The low percent purity is likely attributed to impurities in the sample or incomplete reaction.