Question

Calculate the formula unit mass of sugar (${C_{12}}{H_{22}}{O_{11}}$).

Answer 1

Hint: The key to finding out the formula mass of any given compound is to multiply the atomic mass to the count of each atom that is there in the formula. By utilizing the atomic masses, we can compute the formula mass for every ionic compound. Here the ionic compound is sugar and its empirical formula is given so the only required value is the atomic mass of each atom.

Complete answer:
The formula unit mass is described as the total value that is resulted when the product of atomic mass of an element times the number of atoms of that element present in that compound are added together. Its standard unit is ‘amu’.
It is basically the molecular mass of ionic compounds.
We are given the empirical or chemical formula for sugar as follows:
${C_{12}}{H_{22}}{O_{11}}$
From this formula we know the number of atoms of each element that are found in the compound ‘sugar’. They are:
Number of atoms of carbon $(C) = 12$
Number of atoms of hydrogen $(H) = 22$
Number of atoms of oxygen $(O) = 11$
We also know the fixed atomic masses of each element are as follows:
Atomic mass of carbon $(C) = 12\;amu$
Atomic mass of hydrogen $(H) = 1\;amu$
Atomic mass of oxygen $(O) = 16\;amu$
Then the formula unit mass of sugar is computed as follows:
Formula unit mass = Sum (Atomic mass of each element multiplied by total number of atoms)
$ \Rightarrow {C_{12}}{H_{22}}{O_{11}} = 12 \times 12\;amu + 22 \times 1\;amu + 16 \times 11\;amu$
$ \Rightarrow {C_{12}}{H_{22}}{O_{11}} = (144 + 22 + 176)\;amu$
Calculating the sum:
$ \Rightarrow {C_{12}}{H_{22}}{O_{11}} = 342\;amu$
Therefore the final value of formula unit mass of sugar is calculated to be $342\;amu$.

Note:
The word 'formula unit mass' is utilized for computation of ionic compound's mass, and in the same way 'molecular mass' is utilized for computation of the molecules' mass. The main explanation for why we use two distinct terms is because an ionic compound cannot be a molecule, determining its molecular mass makes very little sense, so we simply refer to it as the "formula mass" when discussing ionic compounds.