4.50 g Mg burns partly to MgO and partly to Mg₃N₂. The residue forms 100 mL NH₃ solution, with all generated NH₃ retained. pH=11.4. Assume Mg(OH)₂ completely insoluble, K b ( N H 3 ) = 2 × 1 0 − 5

Question

4.50 g Mg burns partly to MgO and partly to Mg₃N₂. The residue forms 100 mL NH₃ solution, with all generated NH₃ retained. pH=11.4. Assume Mg(OH)₂ completely insoluble, K b ​ ( N H 3 ​ ) = 2 × 1 0 − 5 ,log2=0.3, α ≪ 1 . Which statements are incorrect?

TestHub · Accepted Answer

log2=0.3 gives [OH⁻]=0.0025 M at pOH2.6. For small ionisation, C≈[OH⁻]²/K_b=0.3125 M and α≈0.008, making A,B true. NH₃ amount in 100 mL=0.03125 mol. Mg₃N₂ hydrolysis makes two NH₃ per three Mg, so Mg in nitride=0.046875 mol. Total Mg=4.5/24=0.1875 mol, hence 25% nitride and 75% oxide. C,D reverse those fractions and are the incorrect statements asked for.

Chemistry - Ionic Equilibrium Question with Solution | TestHub

Options:(select one or more)

Doubts & Discussion