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EEJ MAIN Chemistry QUESTION #7188
Question 1
Determine the oxidation states of Chromium ($Cr$) in the following three species respectively: $[Cr(C_{6}H_{6})_{2}]$, $[Cr(H_{2}O)_{6}]Cl_{3}$, and $K_{2}[Cr(CN)_{2}(O)_{2}(O_{2})(NH_{3})]$.
  • $+3, 0, and +6$✔️
  • $+3, 0, and +4$
  • $+3, +4, and +6$
  • $+3, +2, and +4$
Correct Answer Explanation

Calculation of oxidation states:

  • $[Cr(C_{6}H_{6})_{2}]$: Benzene is a neutral ligand, so $Cr$ is in $0$ oxidation state.
  • $[Cr(H_{2}O)_{6}]Cl_{3}$: $H_{2}O$ is neutral and there are 3 $Cl^{-}$ ions, so $x + 0 = +3 \Rightarrow x = +3$.
  • $K_{2}[Cr(CN)_{2}(O)_{2}(O_{2})(NH_{3})]$: $K$ is $+1$, $CN$ is $-1$, $O$ (oxo) is $-2$, $O_{2}$ (peroxo) is $-2$, and $NH_{3}$ is $0$. $2(+1) + x + 2(-1) + 2(-2) + (-2) + 0 = 0 \Rightarrow x = +6$.
[cite: 13]