E-85 is an alternative fuel for automobiles and light trucks...

E-85 is an alternative fuel for automobiles and light trucks that consists of $85 \%$ (by volume) ethanol, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$ and $15 \%$ gasoline. The density of ethanol is $0.79 \mathrm{g} / \mathrm{mL}$ How many moles of ethanol are in a gallon of $\mathrm{E}-85 ?$

Key Concepts

Fuel Mixture Composition

This concept involves understanding that certain fuels are blends of multiple components, each contributing a specified percentage by volume or mass. Interpreting a fuel mixture’s composition is essential in determining the quantity of a particular component, such as ethanol, within a given total volume.

Volume Unit Conversion

Unit conversion is a critical step in many engineering and chemistry problems. It involves translating a measurement from one unit system to another; for instance, converting gallons to milliliters. This process ensures that all calculations are performed using consistent units, particularly when applying density or other physical constants.

Density and Mass Conversion

Density bridges the gap between volume and mass. Knowing the density of a substance allows one to convert a specific volume into its mass. This step is important when a problem provides physical dimensions in volume but requires mass for further calculations, such as converting to moles using the substance’s molar mass.

Molar Mass and Mole Calculation

Molar mass is a fundamental concept that relates the mass of a substance to the amount of substance in moles. By dividing the mass of a substance by its molar mass, one obtains the number of moles. This concept is central to understanding stoichiometry in chemical reactions and determining the molecular quantity of compounds in a given sample.

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