Question

In an experiment, 4g of M2Ox oxide was reduced to 2.8g of the metal. If the atomic mass of the metal is 56 g mol^-1, the number of O atoms in the oxide is

(A) 1
(B) 2
(C) 3
(D) 4

Answer 1

moles of 2 atom of metal = 2.8÷(2×56)=1/40 mol
mass of oxygen in compound =4-2.8=1.2g
therefore atoms of oxygen (x)=mass of oxygen÷(no. of moles of compound or metal×molar mass of O)=1.2÷(16×1/40)=1.2×40÷16=3
hence 3 is the required answer

Answer 2

Answer: (C) 3

Explanation:

Mass of oxygen in oxide=4-2.8=1.2

Equivalent weight of metal = (mass of the metal/mass of oxygen combined)×8

=(2.8/1.2)×8=18.67 g eq mol^-1

Valency of metal= atomic weight of metal/equivalent weight of metal

=56/18.67=2.99~3

Hence the number of O atoms in the oxide is 3