Passage-based question from...Kaplan MCAT Qbank
Passage excerpt:
" Copper (II) is generally stable in aqueous solutions, and many copper (II) compounds are well-known. However, copper (I) cation is not stable in aqueous solutions.
Initially unaware of this fact, a student planned to prepare copper (I) iodide by treating copper (II) with a mild reducing agent in the presence of iodide. The student was surprised when when adding a soluble copper (II) salt to the solution of potassium iodide when a precipitate formed immediately: revealed to be Cu2I2 ("copper (I) iodide"). Blah blah blah.
Question:
What is the most likely reason for the apparent stability of Cu2I2 ?
A. The copper is actually in the +2 oxidation state.
B. Cu2I2 contains copper in both the 0 and +2 oxidation state.
C. The potassium from the KI keeps it from being oxidized.
D. It does not react because it is insoluble.
Can someone explain this? The answer is D. How was I supposed to know that B is incorrect? There are many examples of compounds, usually oxides, containing elements in two oxidation states. Help!
Passage excerpt:
" Copper (II) is generally stable in aqueous solutions, and many copper (II) compounds are well-known. However, copper (I) cation is not stable in aqueous solutions.
Initially unaware of this fact, a student planned to prepare copper (I) iodide by treating copper (II) with a mild reducing agent in the presence of iodide. The student was surprised when when adding a soluble copper (II) salt to the solution of potassium iodide when a precipitate formed immediately: revealed to be Cu2I2 ("copper (I) iodide"). Blah blah blah.
Question:
What is the most likely reason for the apparent stability of Cu2I2 ?
A. The copper is actually in the +2 oxidation state.
B. Cu2I2 contains copper in both the 0 and +2 oxidation state.
C. The potassium from the KI keeps it from being oxidized.
D. It does not react because it is insoluble.
Can someone explain this? The answer is D. How was I supposed to know that B is incorrect? There are many examples of compounds, usually oxides, containing elements in two oxidation states. Help!