In the mineral , spinel, having the formula MgAl_2O_4, oxide ions are arranged in the cubic close packing , Mg^(2+) ions occupy the tetrahedral voids while Al^(3+)ions occupy the octahedral voids. (i)What percentage of tetrahedral voids is occupied by Mg^(2+) ions ? (ii)What percentage of octahedral voids is occupied by Al^(3+) ions ?

In the mineral , spinel, having the formula MgAl_2O_4, oxide ions are

1.	In the mineral , spinel, having the formula MgAl_2O_4, oxide ions are arranged in the cubic close packing , Mg^(2+) ions occupy the tetrahedral voids while Al^(3+)ions occupy the octahedral voids. (i)What percentage of tetrahedral voids is occupied by Mg^(2+) ions ? (ii)What percentage of octahedral voids is occupied by Al^(3+) ions ?
Answer» Solution :According to the formula `MgAl_2O_4`, if there are 4 oxide ions, there will be `1 Mg^(2+)` ion and `2 Al^(3+)` ions. But if the `4 O^(2-)` ions are in ccp arrangement, there will be 4 octahedral VOIDS and 8 tetrahedral voids. Thus, `1 Mg^(2+)` ions is present in ONE of 8 tetrahedral voids `therefore` % of tetrahedral voids OCCUPIED by `Mg^(2+)=1/8xx100=12.5%` Similarly, `2 Al^(3+)` ions are present in two octahedral voids out of 4 AVAILABLE `therefore` % of octahedral voids occupied by `Al^(3+) =2/4xx100=50%`