how do you calculate the mole percent for a mixture

Question

 calculate the mole percent for a mixture of 40 mL of methyl butyrate (MW 102.1 g/mol, d=0.89g/ml) and 10 mL butyric acid (MW=88.1 g/mol, d=0.96g/mL)

Answer 1

Calculate moles of each and then divide moles of each by the total number of moles present.

Moles methyl butyrate = 40 ml x 0.89 g/ml x 1 mol/102.1 g = 0.3487 moles = 0.3 moles (1 significant digit)

Moles butyric acid = 10 ml x 0.96 g/ml x 1 mole/88.1 g = 0.109 moles = 0.1 moles (1 significant digit)

Total moles = 0.4 moles

Mole fraction methyl butyrate = 0.3 moles/0.4 moles = 0.75

Mole fraction butyric acid = 0.25

Since you really asked for mole %, just multiply by 100 to get 75% and 25% respectively.