Question

How many molecules of ethanol (c2h5oh) (the alcohol in alcoholic beverages) are present in 160 ml of ethanol? the density of ethanol is 0.789 g/cm3. n =?

Answer 1

Note: 1 ml = 1 cm^3

Density = mass / volume
mass = density x volume
mass = 0.789 x 160 = 126.24 grams

From the periodic table:
mass of carbon = 12 grams
mass of hydrogen = 1 grams
mass of oxygen = 16 grams
molar mass of ethanol = 2(12) + 5(1) + 16 +1 = 46 grams

number of moles = mass / molar mass
number of moles = 126.24 / 46 = 2.744 moles

Each mole contains Avogadro's number of molecules.
Therefore:
number of molecules = 2.744 x 6.02 x 10^23 = 1.6518 x 10^24 molecules