Finding Percentage Yield and Purity
Definition of Yield?
Definition of Purity?
Read page 84.
Whenever an experiment is carried out, scientist like to calculate precisely how much product would be obtained. This is called the calculated yield. Also known as theoretical yield. For example,
Salicylic acid -> aspirin
How much of aspirin should we obtain from calculation if 100.0g of salicylic acid was used in this reaction?
Look at the chemical formula of salicylic acid, C7H6O3
So there are 7 C, 6 H and 3 O.
Hence the relative molecular mass is
7 x 12 + 6 x 1 + 3 x 16 = 138
Hence the number of mole of salicylic acid is 100g / 138 = 0.725 moles
So, 1 mole of salicylic acid will produce 1 mole of aspirin.
Hence 0.725 mole salicylic acid will produce 0.725 mole of aspirin.
Calculated mass of aspirin will be 0.725 mole X relative atomic mass of aspirin.
[NOTE: Relative atomic mass of aspirin is 180]
So, 0.725mole X 180 = 130.5g
BUT!!! WOULD YOU OBTAIN 130.5g?
Since we will not obtain 130.5g, so the amount you would get from experiment is called actual yield.
From the question, actual yield is 121.2g
% yield = 121.2g / 130.5g X 100% = 92.9%