0.422 g of an element z reacts with oxygen to form 0.797 g of the oxide z2o3. what is the element z?

Total mass of oxide z2o3 is 0.797g 
 mass of element z in the oxide is 0.422g 
 therefore, mass of oxygen in the oxide is 0.797 - 0.422 = 0.375 g   
 Number of moles of oxygen in the oxide = 0.375/16 = 0.02344 (atomic mass
of oxygen=16)   
 From the given chemical formula of oxide, we know that, the element z and
oxygen are in the ratio of 2:3. So, number of moles of z is 0.02344 *2/3 =
0.015625 
 Hence, atomic mass of z should be = 0.422/0.015625 = 27   
 Element with atomic mass 27 is Aluminium. The oxide is Al2o3

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