Question

For each of the following balanced equations, write theoxidation number above the symbol of each atom thatchanges the oxidation state in the course of the reactions.

(a) $\mathbf{2}{\mathbf{PF}}_{\mathbf{2}}\mathbf{I}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{+}\mathbf{2}\mathbf{Hg}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{}\mathbf{\to }{\mathbf{P}}_{\mathbf{2}}{\mathbf{F}}_{\mathbf{4}}\left(g\right)\mathbf{+}{\mathbf{Hg}}_{\mathbf{2}}{\mathbf{I}}_{\mathbf{2}}\left(s\right)$

(b)$\mathbf{2}\mathbf{KClO}\mathbf{3}\left(s\right)\mathbf{\to }\mathbf{2}\mathbf{KCl}\left(s\right)\mathbf{+}\mathbf{3}\mathbf{O}\mathbf{2}\left(g\right)$

(c)$\mathbf{4}\mathbf{NH}\mathbf{3}\left(g\right)\mathbf{+}\mathbf{5}\mathbf{O}\mathbf{2}\left(g\right)\mathbf{\to }\mathbf{4}\mathbf{NO}\left(g\right)\mathbf{+}\mathbf{6}\mathbf{H}\mathbf{2}\mathbf{O}\left(g\right)$

(d)$\mathbf{2}\mathbf{As}\left(s\right)\mathbf{+}\mathbf{6}\mathbf{NaOH}\mathbf{\left(}\mathbf{l}\mathbf{\right)}\mathbf{\to }\mathbf{2}{\mathbf{Na}}_{\mathbf{3}}{\mathbf{AsO}}_{\mathbf{3}}\left(s\right)\mathbf{+}\mathbf{3}{\mathbf{H}}_{\mathbf{2}}\left(g\right)$

Short answer

The oxidation number is the property of an atom that shows the number of electrons lost or gained by a respective atom.

Step-by-step solution

Step 1:Oxidation and reduction.

a.$2{\mathrm{PF}}_2\mathrm{I}\left(\mathrm{l}\right)+2\mathrm{Hg}\left(\mathrm{l}\right)\to {\mathrm{P}}_2{\mathrm{F}}_4\left(\mathrm{g}\right)+{\mathrm{Hg}}_2{\mathrm{I}}_2\left(\mathrm{s}\right)$

The oxidation state of the atom of the reactant.

1. P: +3
2. F: -1
3. I: -1
4. Hg: 0

The oxidation state of the atom of the product.

1. P: +2
2. F: -1
3. I: -1
4. Hg: +1

b.$2\mathrm{KClO}3\left(\mathrm{s}\right)\to 2\mathrm{KCl}\left(\mathrm{s}\right)+3\mathrm{O}2\left(\mathrm{g}\right)$

The oxidation state of the atom of the reactant.

1. K: +1
2. Cl: +5
3. O: -2

The oxidation state of the atom of the product.

1. K: +1
2. Cl: -1
3. O: 0

Ammonia and Arsenic.

c.$4\mathrm{NH}3\left(\mathrm{g}\right)+5\mathrm{O}2\left(\mathrm{g}\right)\to 4\mathrm{NO}\left(\mathrm{g}\right)+6\mathrm{H}2\mathrm{O}\left(\mathrm{g}\right)$

The oxidation state of the atom of the reactant.

1. N: -3
2. H: +3
3. O: 0

The oxidation state of the atom of the product.

1. N: +2
2. H: 0
3. O: -2

d.$2\mathrm{As}\left(\mathrm{s}\right)+6\mathrm{NaOH}\left(\mathrm{l}\right)\to 2{\mathrm{Na}}_3{\mathrm{AsO}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\left(\mathrm{g}\right)$

The oxidation state of the atom of the reactant.

1. As: 0
2. Na: +1
3. O: -2
4. H: +1

The oxidation state of the atom of the reactant.

1. As: +3
2. Na: +3
3. O: -6
4. H: 0