Question

A solution is prepared by mixing 200.0 g of water, H2O, and 300.0 g of
ethanol, C2H5OH. Determine the mole fractions of each substance.

Answer 1

Answer:

Mole Fraction (H₂O)  =  0.6303

Mole Fraction (C₂H₅OH)  =  0.3697

Explanation:

(Step 1)

Calculate the mole value of each substance using their molar masses.

Molar Mass (H₂O): 2(1.008 g/mol) + 15.998 g/mol

Molar Mass (H₂O): 18.014 g/mol

200.0 g H₂O            1 mole
---------------------  x  ------------------  =  11.10 moles H₂O
                                 18.014 g

Molar Mass (C₂H₅OH): 2(12.011 g/mol) + 6(1.008 g/mol) + 15.998 g/mol

Molar Mass (C₂H₅OH): 46.068 g/mol

300.0 g C₂H₅OH              1 mole
----------------------------  x  --------------------  =  6.512 moles C₂H₅OH
                                         46.068 g

(Step 2)

Using the mole fraction ratio, calculate the mole fraction of each substance.

                                            moles solute
Mole Fraction  =  ------------------------------------------------
                               moles solute + moles solvent

                                                  11.10 moles H₂O
Mole Fraction  =  -------------------------------------------------------------
                               11.10 moles H₂O + 6.512 moles C₂H₅OH

Mole Fraction (H₂O)  =  0.6303

                                             6.512 moles C₂H₅OH
Mole Fraction  =  -------------------------------------------------------------
                               11.10 moles H₂O + 6.512 moles C₂H₅OH

Mole Fraction (C₂H₅OH)  =  0.3697