Q4.71P - Chemistry: Molecular Nature Of Matter And Change

Question

Give the oxidation number of chromium in the following:

$$\begin{gathered} \left(a\right)Cr{O}_3 \\ \left(b\right)C{r}_2{O}_7^{2-} \\ \left(c\right)C{r}_2{\left(S{O}_4\right)}_3 \end{gathered}$$

Step-by-Step Solution

Answer

You need to provide the oxidation number of chromium for the given compounds.

Step 1: Oxidation state of chromium in CrO 3

Oxidation state of Oxygen is -2.

Let, oxidation state of chromium in CrO₃ is x.

No you can write,

  $$\begin{gathered} x+3\left(-2\right)=0 \\ x=+6 \end{gathered}$$

Hence, oxidation state of chromium in CrO₃ is +6.

Step 2: Oxidation state of chromium in Cr 2 O 7 2-

Oxidation state of Oxygen is -2.

Let, oxidation state of chromium in Cr₂O₇^2- is y.

No you can write,

  $$\begin{gathered} 2y+7\left(-2\right)=-2 \\ 2y=+12 \\ y=+6 \end{gathered}$$

Hence, oxidation state of chromium in Cr₂O₇^2- is +6.

Step 3: Oxidation state of chromium in Cr 2 (SO 4 ) 3

Oxidation state of SO₄ is -2.

Let, oxidation state of chromium in Cr₂(SO₄)₃ is z.

No you can write,

  $$\begin{gathered} 2z+3\left(-2\right)=0 \\ 2z=+6 \\ z=+3 \end{gathered}$$$$\begin{gathered} 2z+3\left(-2\right)=0 \\ 2z=+6 \\ z=+3 \end{gathered}$$

Hence, oxidation state of chromium in Cr₂(SO₄)₃ is +3.