Question

Which molecule has a molecular mass of 28.05 amu?

(a) \({\rm{HC}} \equiv {\rm{CH}}\)

(b)

(c)

Short answer

The total molecular or formula mass of each compound will be:

(a)26 amu

(b)28 amu

(c)30 amu

Step-by-step solution

Determine the molecular mass of part (a)

The molecular mass of a compound is equivalent to the sum of the atomic masses of each element present in that compound.

In\({\rm{HC}} \equiv {\rm{CH}}\), there are 2 carbon and 2 hydrogen atoms, and the atomic mass of 1 carbon and 1 hydrogen atoms are 12 amu and 1 amu, respectively. Therefore, the molecular mass of the compound will be \({\rm{12 }} \times {\rm{ 2 + 1 }} \times {\rm{ 2 = 26 amu}}\)

Determine the molecular mass of part (b)

The molecular mass of a compound is equivalent to the sum of the atomic mass of each element present in that compound.

In\({{\rm{C}}_2}{{\rm{H}}_4}\), there are 4 hydrogen and 2 carbon atoms, and the atomic masses of 1 hydrogen and 1 carbon atom are 1 amu and 12 amu, respectively. Therefore, the molecular mass of the compound will be \({\rm{1 }} \times {\rm{ 4 + 12 }} \times {\rm{ 2 = 28 amu}}\)

Determine the molecular mass of part (c)

The molecular mass of a compound is equivalent to the sum of the atomic mass of each element present in that compound.

In \({{\rm{C}}_2}{{\rm{H}}_6}\), there are 2 carbon and 6 hydrogen atoms, and the atomic mass of 1 carbon and 1 hydrogen atom is12 amu and 1 amu, respectively. Therefore, the molecular mass of the compound will be \({\rm{12 }} \times {\rm{ 2 + 1 }} \times {\rm{ 6 = 30 amu}}\).