Question

What is the formula mass of ethyl alcohol $C_2{H}_{5}OH$ ?

Answer 1

In order to arrive with this answer, we should know the atomic weight of the elements present in the compound in this case, the elements are Carbon, Hydrogen, and Oxygen.

The atomic weight for these elements are the following (expressed to the nearest hundredth):

Carbon = 12.01 g/mol

Oxygen = 16.00 g/mol

Hydrogen = 1.01 g/mol

Now, let's count the total number of each element (expressed in moles) bonded in the compound:

Carbon = 2

Oxygen = 1

Hydrogen = 6

To calculate for the formula, we should multiply the atomic weights of each element to the corresponding number of moles in the the compound.

$Carbon:12.01\times 2=24.02$

$Oxygen:16.00\times 1=16.00$

$Hydrogen:1.01\times 6=6.06$

Formula mass of ethyl alcohol is $46.08g/mole$

The sum is equal to 46.08 grams per mole; wherein grams per mole can also be denoted as an atomic mass unit.