Stoichiometry Worksheet - Answer Key

 

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  1. What is stoichiometry?

    This is when the BALANCED chemical reaction is used to determine proportions of chemicals involved in the reaction.

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  2. What are the basic steps required for most stoichiometry calculations?

    The basic steps that you will follow for most of the stoichiometric problems are.

    1 – Make sure the reaction equation is balanced.
    2 – The “backbone” calculation
    You will be given information about substance A and need to
    answer a question about substance B.  The “backbone” is the
    general method for how you proceed with these calculations.

    3.  

     

  3. Consider:

    Al(s) + NH4ClO4(s)    → Al2O3 (s) + AlCl3 (s) + NO (g) +  H2O (g)

    What mass of ammonium perchlorate should be used for every kg of Al?

    4.355 kg NH4ClO4\

    4.  

     

  4. Consider:

    5CO2 + 55NH4+ + 76O2    → C5H7O2 + 54NO2– + 52H2O + 109H+

    How much bacterial tissue (C5H7O2) is produced in a treatment plant for every 1.0 x 104 kg of waste water containing 3.0% NH4+ by mass?  Assume that 95% of the ammonium ions are consumed by bacteria.

    32 kg bacterial tissue

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  5. What is a limiting reactant?  How does it affect a reaction?

    Reactant/reagent used up first in a reaction.  The limiting reactant puts a cap on the amount of product that can be produced.

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  6. What clue indicates that you are dealing with a limiting reactant stoichiometry calculation?

    If you are given information that would allow you to calculate for the moles of more than one reactant.

    7.  

     

  7. Consider:

    2 C6H5Cl + C2HOCl3    → C14H9Cl5 + H2O

    1142 g of chlorobenzene (C6H5Cl) is reacted with 485 g of chloral (C2HOCl3).
    • What mass of DDT (C14H9Cl5) is formed?

      1.167 g DDT
    • What is the limiting reactant?

      Chloral
    • How much reactant is left?

      0 g chloral

      401 g chlorobenzene.

     

     

  8. What is the percent yield?

    The percent of the theoretical output that was actually produced.

    • What is the formula used to solve for it?

      .    actual yield    .    x 100 = %yield
      theoretical yield

     

     

  9. Consider:

    P4 (s) + F2 (g)    → 4PF3 (g)

    How many grams of F2 are needed to produce 120.0g of PF3 if the reaction has a 78.1% yield?

    99.8 g F2

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