Often in a chemical reaction, the theoretical yield (the maximum amount of a product that could be formed given the amount of the reactant) is not obtained.
For this reason, it is useful to calculate the percentage yield to find out the efficiency of the reaction.
Percentage yield= yield obtained/theoretical yield x 100
Exam Question Example:
In an experiment to displace copper from copper sulfate, 6.5g of Zinc was added to an excess of copper (II) sulfate solution. The copper was filtered off, washed and dried. The mass of copper obtained was 4.8g.
Calculate the percentage yield of copper
The equation for the reaction is Zn(s) + CuSo₄(aq) ---> ZnSo₄ (aq) + Cu (s)
1. Calculate the amount, in moles, of zinc reacted
Amount of zinc = 6.5/65 = 0.10mol
2. Calculate the maximum amount of copper that could be formed
Maximum amount of copper = 0.10 mol
3. Calculate the maximum mass of copper that could be formed
Maximum mass of copper = (0.10 x 64)= 6.4g
4. Calculate percentage yield of copper
Percentage yield = 4.8/6.4 x 100 = 75%
isn't the percentage yield of copper 4.8/6.5 x 100 ? where did the 6.4 come from ?
ReplyDeleteNo, the mass number of copper is 63.546. It is rounded up to 64, 0.1 moles of zinc in not the same as 0.1 moles of copper.
DeleteIt's 4.8/6.5 x 100. The equation states that it should be the mass given over the theoretical mass. I'm afraid that no mole calculations should be done.
ReplyDelete