Question

A metal oxide has the formula M2O. It can be thermally decomposed to the metal and oxygen . 5.8 g of the metal oxide forms 400 mg of oxygen gas on complete decomposition. The atomic weight of the metal is 1. 56 2. 23 3. 27 4. 108

Answer 1

The chemical equation for the thermal decomposition of the oxide is as follows:
  
          2M2O  ---------------->   4M    +        O2

Therefore 2 moles of the oxide produces 4 moles of the metal and 1 mole of oxygen in terms of ratio.

The actual mole of oxygen produced is:

moles = mass/molar mass
           =0.4/16
           = 0.025 moles
mole ratio between metal and oxygen = 4:1
therefore moles of the metal = 4 x 0.025 = 0.1 moles

The mass of the metal is 5.8 - 0.4 = 5.4 g
moles = mass/mm
mass= mm x moles
mm= mass/moles
   =  5.4/0.1
    =54