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General Chemistry

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Chemical Reactions

Question
12 out of 15
 

Passage 1

Information regarding the amounts of substances that actually react to form the products are of extreme help. Analyzing reactions and having the balanced equations help chemists to determine the correct and optimum proportions of reactants to be used. There are various other factors besides the amount of reactants, which determine the efficiency of reactions.

Experiment 1

Student 1 used 40.5 g of aluminum and 80 g of Fe2O3 for Reaction I. A second student conducted the same reaction with a different amount for one of the reactants. The second student used 40.5 g of aluminum, and 90 grams of Fe2O3. A third student also conducted the same reaction with 54 g of aluminum and the same amount of Fe2O3 used by the first student.

Experiment 2

Reaction II involved the production of Al2O3 from aluminum hydroxide This was done by heating aluminum hydroxide.


Experiment 3


Which of the following changes will further increase the overall yield for the reactions conducted in the Experiment 1?

A Increasing the amount of aluminum used by Student 1
B Increasing the amount of aluminum used by Student 2
C Increasing the amount of Fe2O3 used by Student 2
D None of the above

Ans. C By increasing the amount of aluminum used by the first student, there will not be an increase in the yield because Fe2O3 is the limiting reagent. Hence, Choice A is not correct. The same reasoning rules out Choice B. Increasing the amount of Fe2O3 by the second student will increase the yield further, because we actually have unreacted Al left according to the amounts used in the experiment. Hence, if we further increase the amount of Fe2O3 used, it will increase the yield until the Al runs out. Choice D is wrong.

Chemical Reactions Flashcard List

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