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chemistry igcse acapprinted 21 · PDF 21
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21
The actual yield is the recorded amount of product obtained.
• The theoretical yield is the amount of product that would be obtained under perfect,
practical, and chemical conditions .
• The Theoretical yield is calculated from the balanced equation and the reacting masses.
• The percentage yield compares the actual yield to the theoretical yield.
• For economic reasons, the objective of every chemical producing company is to have as
high a percentage yield as possible to increase profits and reduce costs and waste.
• To calculate percentage yield, the following equation is used:
Percentage Purity
• A pure substance has nothing else mixed with it.
• Often, the product you are trying to obtain may become contaminated with unwanted
substances such as unreacted reactants, catalysts and other impurities.
• To calculate percentage purity, the following equation is used:
• The actual yield (in percentage yield), and the total mass of substance (in percentage
purity) are always given in the question.
Questions
P2 :
1. When 2 g of hydrogen gas reacts completely with oxygen, what mass of water is formed?
A) 9 g
B) 18 g
C) 36 g
D) 4.5 g