Question

AN ionic compound of element M and chlorine has the formula MCl3 . the molecular mass os MCL3 is 118.5 . What is the molecular mass of the oxide of element M ?

1. 28
2. 44
3. 72
4. 99

Answer 1

Molecular mass of MCl₃ is 118.5 u.
Atomic mass of Chlorine is 35.5 u
Atomic mass of Metal = molecular mass of MCl₃ - mass of Chloride
= 118.5 - (3$\times$35.5)
= 12 u
Atomic mass of Metal is 12 u
The compound MCl₃ shows metal has valency 3. So, it form oxide of molecular formula M₂O₃.
Molecular mass of M₂O₃ is (2$\times$12) + (3$\times$16)
= 24 + 48
= 60 u