Aspirin prac

[Jason12]

what are some potential errors in the making of aspiring other than transfer errors?

Also how do I calculate percentage yield?

[something5678]

Errors:
- Impurities in aspirin (such as undissolved salicylic acid) produced contributing to a higher final mass and a higher percentage yield
- Small amounts of aspirin falling through filter paper contributing to a lower final mass and a lower percentage yield
- Reaction not going to completion, there was not enough ethanoic acid (or ethanoic anhydride) to react all of the salicylic acid, therefore some salicylic acid is still in solution leading to the mass of the final product being lower and lower percentage yield
- The salicylic acid you originally used may have contained some impurities this would lead to an overall lower mass of produced aspirin and a lower than expected percentage yield.
- Scales not calibrated properly, or weighing final product and initial product on different scales

Assume you measured out 2.034g salicylic acid, and you got a final mass of acetylsalicylic acid (aspirin) of 2.134g

Percentage yield can be calculated by:
1. find number of mole of salicylic acid reacted
n=m/Mr
n(salicylicacid) = 2.034/138 = 0.014739 mol

2. find number of mole of acetylsalicylic acid produced 
since they are in a 1:1 ratio, the number of mole of salicylic acid reacted = number of mole of acetylsalicylic acid produced
n(acetylsalicylic acid) = n(salicylic acid) = 0.014739 mol

3. find expected mass of acetylsalicylic acid produced
m=n X Mr
m(acetylsalicylic acid) = 0.014739 X 180 = 2.6530g

4. Express your experimental mass as a percentage of your expected mass
experimental mass = 2.134g
expected/theoretical mass = 2.6530g
% yield = experimental mass/expected mass X100 = 2.134/2.6530 X100 = 80.44%

The percentage yield tells us how efficient the experiment was, i.e. what percentage of the reactants actually became the products.
In this case, the percentage yield was 80.44% This means that the reaction was 80.44% efficient, producing 80.44% of the total possible mass
If it was 100% efficient, the experimental mass would be 2.6530g the experiment would need to be error free and every single salicylic acid molecule would have reacted with an ethanoic acid molecule.

Hope this helped