Question

When you mixed 20 grams of magnesium and an excess of nitric acid, 1.7 grams of hydrogen was actually produced. What is the percent yield of hydrogen during this reaction?
Mg + 2HNO3 Mg(NO3)2 + H2

Select one of the options below as your answer:



A.
3.3 %




B.
48.5 %




C.
25.7 %




D.
40 %




E.
42.5 %

Answer 1

Based on the balanced chemical reaction presented above, every mole of magnesium (Mg) yields one mole of diatomic hydrogen (H2). When converted to masses, every 24.3 grams of magnesium yields 2 grams of hydrogen. 

From the given, there are 20 grams of magnesium available for the reaction. With this amount, the expected yield of hydrogen is 1.646 grams. To calculate the percent yield, divide the actual yield to the hypothetical yield.

*The case is impossible because the actual yield is greater than the theoretical yield.

If we assume that there had been a typographical error and that the actual yield is 0.7 grams instead of 1.7 grams, the percent yield becomes 42.5%. Thus, the answer is letter E. 

Answer 2

PLATO USERS answer is B