Consider a reaction of chemicals depicted as a + b → c + d. suppose reaction of 21.8 grams of a with 40.7 grams of b gave 31.8 grams of c. however, the theoretical yield of c for this reaction was 49.9 grams. what was the percent yield of chemical c?

The theoretical yield of C was 49.9 g. However the actual yield was 31.8 g.
to find the percent yield of C, the following formula can be used,
percent yield of C = actual yield / theoretical yield x 100%
percent yield of C = 31.8 g / 49.9 g x 100%
                             = 63.7%
most of the time only a percentage of the theoretical yield is the actual yield.
the percent yield of C is 63.7%

The answer is c) pyrite

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