JIPMER2015ChemistrySolid State
Ferrous oxide has a cubic structure. The length of edge of the unit cell is 5 Å and the density of the oxide is 4.0 ~g ~cm ⁻³ . Then the number of Fe ²⁺ and O ²⁻ ions present in each unit cell will be
Options
- Afour Fe ²⁺ and two O ²⁻
- Bfour Fe ²⁺ and four O ²⁻
- Ctwo Fe ²⁺ and four O ²⁻
- Dtwo Fe ²⁺ and two O2-
Correct answer
B. four Fe ²⁺ and four O ²⁻
Step-by-step solution
aligned & d= Z M N_A V & Z= d N_A V M aligned As a=5 Å=5 10⁻⁸ ~cm V= (5 10⁻⁸ )^3 ~cm ^3 Molecular mass, M=56+16=72 ~g aligned Z & = 4 6.023 10²³ (5 10⁻⁸ )^3 72 & =4.16 4 aligned Four molecules of ferrous oxide, FeO per unit cell, it means that 4 Fe ²⁺ and 4 O ²⁻ ions are present in each unit cell.