Question

What is the oxidation number of H in ${\mathrm{AlH}}_3$?

Answer 1

1. The oxidation number or the oxidation state of an atom or compound denotes the loss or gain of electrons.
2. The loss or gain in electrons will stabilize the molecule.
3. Aluminium hydride$\left({\mathrm{AlH}}_3\right)$ is metal hydride in which Aluminium is the electropositive element.

Elements with a given Oxidation number

• Aluminium loses its 3 electrons to achieve the stable electronic configuration.
• Therefore, the oxidation state of Aluminium is +3.

Step 2: Calculating the oxidation number of H in$\left({\mathrm{AlH}}_3\right)$

• Let the oxidation number of Hydrogen be x.
• Equation all the values to 0.
• $(\mathrm{No}.\mathrm{of}\mathrm{atoms}\mathrm{of}\mathrm{Aluminium})\times \left(\mathrm{Oxidation}\mathrm{No}.\mathrm{of}\mathrm{Aluminium}\right)+(\mathrm{No}.\mathrm{of}\mathrm{atoms}\mathrm{of}\mathrm{Hydrogen})\times \left(\mathrm{Oxidation}\mathrm{No}.\mathrm{of}\mathrm{Hydrogen}\right)=0$
• $1\left(3\right)+3\left(\mathrm{x}\right)=0$
• $\mathrm{x}=-1$
• Thus, the oxidation state of Hydrogen in Aluminium hydride is -1.