Question

Oxidation states of Cr in K2Cr2O7 and CrO5 are, respectively:

• A. +6, +5
• B. +6, +10
• C. +6, +6
• D. None of these

Answer 1

The Correct Option is C

The correct answer is +6, +6.

Here's how we determine the oxidation states:

• K₂Cr₂O₇ (Potassium Dichromate):
  • The oxidation state of K is +1.
  • The oxidation state of O is -2.
  • Let the oxidation state of Cr be x.
  • The compound is neutral, so the sum of the oxidation states must be zero: 2(+1) + 2(x) + 7(-2) = 0 2 + 2x - 14 = 0 2x = 12 x = +6
  • Therefore, the oxidation state of Cr in K₂Cr₂O₇ is +6.
• CrO₅ (Chromium Pentoxide):
  • CrO₅ has a "butterfly" structure with two peroxide linkages (O-O) and one double-bonded oxygen. The structure can be written as CrO(O₂)₂.
  • Each peroxide linkage (O₂^2-) has an oxidation state of -1 for each oxygen atom, hence -2 for the O2 group.
  • The oxidation state of the doubly bonded oxygen is -2.
  • Let the oxidation state of Cr be x.
  • The sum of oxidation states must be zero: x + (-2) + 2(-2) = 0 x - 2 - 4 = 0 x = +6
  • Therefore, the oxidation state of Cr in CrO₅ is +6. (Note: Assigning a simple oxidation state of -2 to each of the five oxygens would incorrectly give chromium an oxidation state of +10. We need to know the real structure)

Therefore, the oxidation states of Cr in K₂Cr₂O₇ and CrO₅ are +6 and +6, respectively.

Correct Answer: +6, +6