NEET Chemistry The Solid State Questions Solved

A spinel is an important class of oxides consisting of two types of metal ions with the oxide ions arranged in ccp layers. The normal spinel has 1/8th of the tetrahedral void occupied by one type of metal and one half of the octahedral voids occupied by another type of metal ions. Such a
spinel is formed by Zn2+, Al3+ and O2- with Zn2+ in tetrahedral void. Give the simplest formula of the spinel.

(A) ZnAl2O4                                 

 (B) ZnAl2O3

(C) ZnAlO                                       

(D) None of these

(A). Let the no. of tetrahedral voids = a
No. of octahedral voids = a/2
1/8 th tetrahedral voids is occupied by Zn2+

 No. of Zn2+=a/8

1/2 of octahedral voids occupied by Al3+

 No. of Al3+=a2×2=a4

Ratio of Zn2+:Al3+

            1  : 2

For 1 mol Zn2+, Al3+=2

Total +ve charge = 2+3×2=8  No. of O2-=4

 The simplest formula will be ZnAl2O4

Difficulty Level:

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