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NCAE Chemistry: An aqueous solution contains 64.0 g of ethanol (C2H5OH) in 122.0 g solution. What    
      is the mole fraction of ethanol in the solution?
             a. 0.205                                                         c. 0.302
             b. 0.432                                                         d. 0.70

Sagot :

Helloiamprinceidn
GIVEN:
Amount of ethanol = 64 grams
Total amount of solution = 122 grams
Amount of water = 122 grams - 64 grams = 58 grams

Molecular weight of C2H50H:
C2 = 12 (2) = 24
H5 = 1 (5) = 5
O = 16
H = 1
TOTAL= 46 grams

Molecular weight of H2O:
H2 = 1(2) = 2
O = 16
TOTAL = 18 grams

STEP 1: Convert grams to moles. 

C2H50H
64 g. C2H50H x 1 mole  = 1.39 moles
                         46 g.

H20
58 g. H20 x 1 mole  = 3.22 moles
                   18 g.

TOTAL MOLES OF THE AQUEOUS SOLUTION:

mol C2H5OH + mol H2O = 1.39 + 3.22 = 4.61 moles

STEP 2: Substitute the given to the formula and solve.

mole fraction = mole of component
                      total mole of solution
                    = mole of C2H5OH (because it's the one being asked)
                      total mole of solution
                     = 1.39 moles
                        4.61 moles
                     = 0.302 moles