When dealing with questions related to percentage yield calculations, it is important to remember the formula👇
🧐Percentage yield = (Actual yield ÷ Theoretical yield) x 100%
Key Points
- The theoretical yield is the quantity of product predicted from the chemical reaction
- The actual yield is usually less than the theoretical yield due to experimental errors such as incomplete reaction or loss of some products.
Example 1🤓
CaCO3 ⇒ CaO + CO2
In the above reaction, the expected theoretical yield of CaO obtained from 100g of CaCO3 is 56g.
However, if the actual yield is only 48g of CaO, what is the percentage yield?
Answer: By substituting the values in the formula,
Percentage yield= (48÷56) x 100% = 86%
Example 2🤓
In an experiment to displace Copper from Copper Sulfate, 6.5 g of Zinc was added to excess Copper (II) Sulphate Solution. The Copper was filtered off, washed and dried. The mass of Copper obtained was 4.8 g. Calculate the Percentage Yield of Copper.
Step 1- Write Down the Equation
🧐Zn (s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
Step 2- Calculate the Moles of Zinc
🧐Moles = Mass ÷ Molar Mass
Moles of Zinc = 6.5 ÷ 65 = 0.10 Mol
Step 3-Find the moles of Copper using the mole ratio
🧐According to the equation, 1 mole of zinc requires 1 mole of copper
Therefore, moles of Copper = 0.10 mol
Step 4- Calculate the mass of the copper by rearranging the equation
Mass of Copper= Moles x Molar Mass = 0.10 x 64 =6.4 g
💪Final Step-Calculate the Percentage of Yield of Copper
Percentage Yield = ( 4.8 ÷ 6.4 ) x 100 = 75%
Example 3🤓
The percentage yield and theoretical yield of ammonia are 15% and 44.2 tonnes respectively. Find the actual yield of ammonia.
🧐Just rearrange the equation to find the actual yield
Actual Yield of Ammonia= 44.2 tonnes x 15% = 6.63 tonnes
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