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Percent Yield

If we know the chemical equation and the amounts of reactants, we can calculate the theoretical yield of that reaction. But in reality, the yield depends on many other factors also. Most of the time in synthesis reactions, even in your own lab experiments, you probably noticed that the actual yield is lower than the theoretical yield. The percent yield denotes the amount of actual yield in terms of the theoretical yield. The formula to find the percent yield is given below:


Example 2-7



A student conducted the above reaction in a lab as a part of her research assignment. She used 138 g of sodium nitrite, with excess of  hydrogen chloride. What is the percent yield of HNO2, if the actual yield of HNO2 was 61.1 g?

First, you should find the number of moles of NaNO2. Since she used 138 g, the number of moles of NaNO2 is 2 (Mol.wt of NaNO2 is 69 g/mol). Since the ratio of formation of HNO2 is 1:1 with respect to NaNO2, theoretically 2 moles of HNO2 should be formed. Two moles of HNO2 correspond to 94 g. But actually, only 61.1 g of HNO2 was formed. Now it is just a matter of plug and chug in the percent yield formula.



In this experiment, the actual yield was not high (i.e., only 65% of the theoretically predicted yield) as expected.


Example 2-8

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