Question: Propose two molecular formulas for each molecular ion: (a) 102; (b) 98; (c) 119; (d) 74.

The mass of a compound can be used for the determination of molecular ions.

The molecular weight of a compound is similar to the mass value of a molecular ion.

a. The molecules ${\text{C}}_{\text{8}}{\text{H}}_{\text{6}}$and ${\text{C}}_{\text{6}}{\text{H}}_{\text{14}}\text{O}$possess molecular mass 102. It can be calculated as-

The molecular mass of ${\text{C}}_{\text{8}}{\text{H}}_{\text{6}}$is$12\times 8+1\times 6=102$

The molecular mass of ${\text{C}}_{\text{6}}{\text{H}}_{\text{14}}\text{O}$is $12\times 6+1\times 14+16=102$

b. The molecules ${\text{C}}_{\text{8}}{\text{H}}_{\text{2}}$and ${\text{C}}_{\text{7}}{\text{H}}_{\text{14}}$possess molecular mass 98. It can be calculated as-

The molecular mass of ${\text{C}}_{\text{8}}{\text{H}}_{\text{2}}$is $12\times 8+1\times 2=98$

The molecular mass of ${\text{C}}_{\text{7}}{\text{H}}_{\text{14}}$is $12\times 7+1\times 14=98$

c. The molecules ${\text{C}}_{\text{8}}{\text{H}}_{\text{9}}\text{N}$and ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{N}}_{\text{3}}$possess molecular mass 119. It can be calculated as-

The molecular mass of ${\text{C}}_{\text{8}}{\text{H}}_{\text{9}}\text{N}$is $12\times 8+1\times 9+14=119$

The molecular mass of ${\text{C}}_{\text{6}}{\text{H}}_{\text{5}}{\text{N}}_{\text{3}}$is $12\times 6+1\times 5+14\times 3=119$

d. The molecules ${\text{C}}_{\text{6}}{\text{H}}_{\text{2}}$and ${\text{C}}_{\text{4}}{\text{H}}_{\text{10}}\text{O}$or ${\text{C}}_{\text{3}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}$possess molecular mass 74. It can be calculated as-

The molecular mass of ${\text{C}}_{\text{6}}{\text{H}}_{\text{2}}$is $12\times 2+2\times 1=74$

The molecular mass of ${\text{C}}_{\text{4}}{\text{H}}_{\text{10}}\text{O}$ is $12\times 4+1\times 10=74$

The molecular mass of ${\text{C}}_{\text{3}}{\text{H}}_{\text{6}}{\text{O}}_{\text{2}}$is $12\times 3+1\times 6+16\times 2=74$