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PCAT Chemical Processes – Nitrous Oxide

  • by Sam
  • Jan 23, 2018
  • PCAT Question of the Day

Amateur chemists make nitrous oxide at home using this reaction:

chemical reaction

How many grams of NH4NO3 are required to produce 134.4 L of mixed gas if products are at STP?

 

  1. 160
  2. 240
  3. 960
  4. 1440
Click for Explanation

This solution has 3 steps: balance the equation, determine the required number of moles of product and reactant, and calculate the mass of reactant necessary. The reaction as written is unbalanced. In the balanced equation, 2 moles of H2O and 1 mole of N2O are made for each 1 mole of NH4NO3. 3 moles of product gas result from each mole of reactant. 22.4 L of gas corresponds to 1 mole of gas at STP, and the specified 134.4 L indicates 6 moles of product gases. 6 moles of mixed product gas requires 2 moles of reactant. NH4NO3 weighs 80 g/mole, so 160 g are required.

A) 160, correct. 2 moles of NH4NO3 yields 4 moles of H2O and 2 moles of N2O, for 6 moles of mixed product gas occupying 134.4 L at STP.

B) 240, incorrect, This answer results from using the unbalanced equation as written.

C) 960, incorrect, This answer results from using the unbalanced equation and calculating the mass of 12 moles NH4NO3 for 6 moles N2O product rather than mixed gas.

D) 1440, incorrect, This answer results from using the correct balanced equation and calculating the mass of 18 moles of NH4NO3for 6 moles of N2O product rather than mixed gas.

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