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PCAT Chemical Processes – Double Displacement of Two Species

  • by Sam
  • Apr 19, 2018
  • PCAT Question of the Day

Lithium hydroxide reacts with silver nitrate in a double displacement reaction. Suppose 48 g of lithium hydroxide and 85 g of silver nitrate are placed in a vessel and react to completion. If 50 g of silver hydroxide is obtained, what is the percent yield of silver hydroxide?

A. 20%
B. 40%
C. 80%
D. 125%

Click for Explanation

C is correct. The balanced chemical equation for the described reaction is below:

LiOH+ AgNO3 → AgOH + LiNO3

Percent yield is calculated by dividing the actual yield (50 g) by the theoretical yield, then multiplying by 100%. First, then, let us find the theoretical yield. To do so, we must figure out which reagent is limiting. Consulting the periodic table allows us to discern that the molar masses of lithium hydroxide and silver nitrate are approximately 24 g/mol and 170 g/mol, respectively. We thus have 2 moles of LiOH and 0.5 moles of AgNO3. Since the stoichiometric ratio of LiOH to AgNO3 is 1:1, AgNO3 is limiting. Finally, note that the molar mass of AgOH is approximately 125 g/mol.

 

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