Calculate the mole fractions of methanol, CH3 OH ; ethanol,...

Calculate the mole fractions of methanol, $\mathrm{CH}_{3} \mathrm{OH} ;$ ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH} ;$ and water in a solution that is $40 \%$ methanol, 40\% ethanol, and 20\% water by mass. (Assume the data are good to two significant figures.)

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Key Concepts

Mole Fraction

Mole fraction is a concentration unit that represents the ratio of the number of moles of a specific component to the total number of moles in a mixture. It is a dimensionless quantity used in chemistry to describe the relative proportions of substances in a solution or mixture.

Conversion from Mass to Moles using Molar Mass

Converting mass to moles involves dividing the mass of a substance by its molar mass, which is the mass per mole of that substance. This conversion is crucial when starting with mass percentages and needing to calculate the number of moles for each component in order to determine mole fractions.

Percent Composition and Assumed Mass Basis

Percent composition by mass provides the proportion of each component in a mixture. By assuming a convenient total mass (e.g., 100 grams), these percentages can be directly converted into mass values for each substance, which are then converted to moles, allowing for the calculation of mole fractions in a solution.

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