Q4.69P - Chemistry: Molecular Nature Of Matter And Change

Question

Give the oxidation number of phosphorus in the following:

$$\begin{gathered} \left(a\right)H_2{P}_2{O}_7^{2-} \\ \left(b\right)P{H}_4^{+} \\ \left(c\right)PC{l}_5 \end{gathered}$$

Step-by-Step Solution

Answer

You need to provide the oxidation no of phosphorus for the given compounds.

Step 1: Oxidation state of phosphorus in H 2 P 2 O 7 2-

Oxidation state of Hydrogen is +1.

Oxidation state of Oxygen is -2.

Let, oxidation state of phosphorus in H₂P₂O₇^2- is x.

No you can write,

  $$\begin{gathered} 2\left(+1\right)+2x+7\left(-2\right)=-2 \\ 2x=+10 \\ x=+5 \end{gathered}$$

Hence, oxidation state of phosphorus in H₂P₂O₇^2- is +5.

Step 2: Oxidation state of phosphorus in PH 4 +

Oxidation state of Hydrogen is +1.

Let, oxidation state of phosphorus in PH₄⁺ is y.

No you can write,

  $$\begin{gathered} y+4\left(+1\right)=+1 \\ y=-3 \end{gathered}$$

Hence, oxidation state of phosphorus in PH₄⁺ is -3.

Step 3: Oxidation state of phosphorus in PCl 5

Oxidation state of Chlorine is -1.

Let, oxidation state of phosphorus in PCl₅ is z.

No you can write,

  $$\begin{gathered} z+5\left(-1\right)=0 \\ z=+5 \end{gathered}$$

Hence, oxidation state of phosphorus in PCl₅ is +5.