SC14a Yields Flashcards
14.1 calculate the percentage yield of a reaction from the actual yield and theoretical yield
14.2 described that the actual yield of a reaction is usually less than a theoretical yield and that the cause of this include:
a. incomplete reactions
b. practical losses
c. unwanted side reaction
What is theoretical yield?
The maximum calculated amount of a product that could be formed from a given amount of reactants
What is actual yield?
The actual amount of a product obtained from a chemical reaction
What is percentage yield?
the actual yield divided by the periodical yield, as a percentage
percentage yield =
Actual yield / theoretical yield x 100
What is the percentage yield if the actual yield is 3.2g and theatrical yield is 4.0g
3.2 / 4.0 = 0.8
0.8 x 100 = 80%
Calculate the percentage yield of aluminium chloride when the reaction is carried out with a 108g aluminium at excess chlorine and 300g of aluminium chloride is produced
2Al + 3Cl2 → 2AlCl3
Mr Al = 27 AlCl3 = 133.5
x ratio 54 267
108g 534
Theoretical yield AlCl3 = 534g
percentage yield = 300/534 x 100 = 56.2 (3 sig fig)
what is practical losses?
Just like baking a cake transferring from one container to another results and losses of reactants / products.
What is competing / unwanted side reactions?
Some of the reactants may react to make a different product, resulting in less of the desired product being made.
Why is a higher percentage yield more useful?
Fewer raw materials required, less waste produced, more product
Calculate the mass of water obtained when sixteen tonnes of hydrogen reactive oxygen.
2H2 + O2 → 2H2O
Mr H2 = 2 H2O = 18
x ratios 4 36
16 144
144 tonnes of water is obtained
