Molecular Mass / Formula Mass

1) Find the formula mass of KMnO₄.
         Total                     158.00 g

2) Find the  formula mass of  Mg₃(PO₄)₂.

         Total                     262.79 g

3) Find the molecular mass of  C₁₂H₂₂O₁₁.

         Total                       342.23 g

Conversion of  Moles, Grams, Molecules, and Atoms

1) How many moles are in 17.7 g of  KMnO₄?    0.112 mol KMnO₄

    How many formula units are in 17.7 g  KMnO₄?  6.747  x 10²²formula units KMnO₄

    How many atoms of O are in 17.7 g  KMnO₄?   2.70  x 10²³ atoms O

2) How many moles are in 41.2 g of  Mg₃(PO₄)₂?  1.57 mol Mg₃(PO₄)₂

    How many formula units are in 41.2 g  Mg₃(PO₄)₂?   9.44 x 10²³ units  Mg₃(PO₄)₂

    How many atoms of P are in 41.2 g  Mg₃(PO₄)₂?   1.89 x 10²⁴ atoms P

3) How many moles are in 26.9 g of  C₁₂H₂₂O₁₁?  0.079 mol C₁₂H₂₂O₁₁

    How many molecules are in  26.9 g of  C₁₂H₂₂O₁₁?  4.73 x 10²²molecules  C₁₂H₂₂O₁₁

 
    How many atoms of C are in 26.9 g of  C₁₂H₂₂O₁₁? 5.68  x 10²³ atoms C

4) How many moles are 19.8 x 10²⁴ molecules C₁₂H₂₂O₁₁?  32.9 mol C₁₂H₂₂O₁₁

  
     What is the mass of  19.8 x 10²⁴ molecules C₁₂H₂₂O₁₁?   1.13x10⁴g C₁₂H₂₂O₁₁

5) How many moles of  Mg₃(PO₄)₂  are  27.6 x 10³⁷ atoms of O in Mg₃(PO₄)₂? 
     5.73 x 10¹³ mol Mg₃(PO₄)₂

6) How many moles of KMnO₄ are 3.64 x 10²⁵ atoms of Mn in KMnO₄?  60.6  mol KMnO₄

Percent Composition

1) Find the percentage composition of  KMnO₄. 

  24.75% K      34.77% Mn       40.48% O

2) Find the percentage composition of  Mg₃(PO₄)₂.

   27.75% Mg       23.57% P    48.68% Mg
                 

3) Find the percentage composition of  C₁₂H₂₂O₁₁.

   42.11% C         6.49% H        51.40% C
       

Empirical Formula

1) What is the empirical formula for a compound if a 83.7 g sample contains 44.28g Al and
     39.42 g O?
          Al₂O₃

2) What is the empirical formula for a compound if a 55.0 g sample contains
     22.0 g C, 3.67 g H, and  29.33 g O?  
     CH₂O

    
Molecular Formula

1) A compound has a percentage composition of 40.01% C,   6.69 % H, and  53.30% O.  Its
     molecular mass is 179.9 amu.  What is it's empirical formula?  What is it's molecular formula?

       CH₂O empirical formula        C₆H₁₂O₆  molecular formula

2) A compound has a percentage composition of  46.68% N and   53.32% O.   Its molecular
     mass  is  59.98 amu.  What is the empirical formula?  What is it's molecular formula?

     NO empirical formula         N₂O₂  molecular formula

Hydrates

1)  A 16.59 g sample of hydrated sodium thiosulfate.  The sample is heated to drive off the
     water.  The dry sample has a mass of 10.59 g of sodium thiosulfate.  What is the formula for
     the hydrate?

          Na₂S₂O₃ * 5H₂O

2)  A 35.64 g sample of hydrated barium bromide.  The sample is heated to drive off the
      water. The dry sample has a mass of 30.42 g of barium bromide.  What is the formula for
      the hydrate?

        BaBr₂ * 2H₂O