Units Worksheet - Answer Key

 

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  1. Units to describe a solution

      2.  

    1. Molarity

      2.  

    2.  Molality

      3.  

    3.  Mole Fraction

      4.  

    4. Mass Percent

     

     

  2. What are the units of molarity?

    Molarity (M) = moles of solute
    L of sol’n

    3.  

     

  3. What are the units of molality?

    Molality (m) = moles of solute
    kg of solvent

    4.  

     

  4. How do you determine the mole fraction?

    Mole Fraction (χA) = moles of “A”
    total moles

    5.  

     

  5. How do you determine the mass percent?

    Mass Percent = mass of “A” x 100
    total mass

    6.  

     

  6. Calculate the molar concentration of all the ions in the following strong electrolytes.
    1. 75g of KCl dissolved in 250 mL of water.

      [K+] = 4.0 M
      [Cl–] = 4.0 M

      2.  

    2. 100.0g of MgF2 dissolved in 500.0 mL of water

      [Mg2+] = 3.21 M
      [F–] = 6.42 M

     

     

  7. An aqueous antifreeze solution is 40.0% ethylene glycol (C2H6O2) by mass.  The density of the solution is 1.05 g/cm3.  Calculate the molality, molarity, and mole fraction of ethylene glycol.

    10.7 m C2H6O2

    6.77 M C2H6O2

    χC2H6O2 = 0.162

    8.  

     

  8. What is a dilution?

    In a dilution the volume of a solution is increased but the moles of solute remains the same.

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  9. What equation is useful in a dilution?

                                                          M1V1 = M2V2

    M1 = Initial molarity                       M2 = Final molarity

     

    V1 = Initial sol’n volume                V2 = Final sol’n volume

    10.  

     

     

  10. How much water must be added to a 2.00M stock sol’n of NaOH to make 100.0 mL of a 0.100M NaOH sol’n?

    95.0 mL water

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