Question

an ionic compound of element M and Chlorine has mcl3. the molecular mass of mcl3 is 118.5 .what will be the molecular mass of oxide of element M

Answer 1

we know the atomic mass of cl= 33.5
so atomic mass o metal= molecular mass of MCl3 - atomic mass of Cl
= 118.5 - (3 x 33.5)
= 12

Th valency of this metal can be predicted as 3 rom the formula, so the oxide will be M2O3
molecular mass of M2O3= (12 x 2) + (16 x3)
= 60 u

Answer 2

mcl3 mass is 118.5
mcl3 mass is mass of M+3* Mass of Cl
So
118.5=mass M + 3*35.5 because of mass of chlorine is 35.5
so the mass of M is 12 U and valency of M is 3 ( we figured it out from MCl3 formula)
and the formula for oxide of M is M203
now the mass of M203 = 2*12 + 3*16 which is 72.