Silver iodide ( ) and silver chloride ( ) both crystallize in the same structure type…
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Silver iodide (AgI) and silver chloride (AgCl) both crystallize in the same structure type at room temperature. A researcher prepares a mixed crystal AgCl0.70I0.30 by randomly substituting I− ions for Cl− ions in the anion lattice while keeping all Ag+ positions fully occupied. Six-coordinate ionic radii are given below.
• Ag+ : 1.15A˚ • Cl− : 1.81A˚ • I− : 2.06A˚
(a) Using the difference in ionic radii, predict qualitatively whether the lattice energy per ion pair of AgCl0.70I0.30 is expected to be greater than, less than, or approximately equal to that of pure AgCl. Provide a concise explanation.
(b) Describe one structural or mechanical consequence (e.g., lattice strain, defect formation) that could arise from the partial substitution of the larger I− ion and explain its origin.
(c) The pure iodide AgI undergoes a solid–solid phase transition to a highly conductive form at 147 °C. Predict, with justification, how introducing 30 mol % I− into AgCl might influence the temperature at which such a transition could occur in the mixed crystal.