Balance the following reactions both by oxidation number method and ion electron method:

As2S3+NO3- +H+ gives AsO43- + S + NO2 + H2O

**Oxidation number method:**

**Step 1:**

The skeleton equation is:

As_{2}S_{3} + NO^{-} _{3}+ H^{+} → AsO^{3-}_{4} + S + NO_{2} + H_{2}O

**Step 2:**

Oxidation number of various atoms involved in the reaction is as follows:

**3+ 2- +5 2- +5 2- 0 +4 -4**

As_{2} S_{3} + NO^{-}_{3} + H^{+} → As O^{3-}_{4} + S + NO_{2} + H_{2}O

**Step 3:**

We can balance S by just observation. For Nitrogen oxidation number changes from +5 to +4 so it is reduced. For Arsenic (As) oxidation number changes from +3 to +5 so it is oxidised.

**Step 4:**

Determine the net increase in oxidation number for the element that is oxidized and the net decrease in oxidation number for the element that is reduced.

For As +3 to +5 Net change = +2

For N +5 to +4 Net change = -1

**Step 5:**

Determine a ratio of oxidized to reduced atoms that would yield a net increase in oxidation number equal to the net decrease in oxidation number.

**As** atoms would yield a net increase in oxidation number of +2 (Two electrons would be lost by one **As** atom.) and 2 N atom would yield a net decrease of -2. (Two N atoms would gain two electrons.)

Thus the ratio of **As** atoms to **N** atoms is 1:2.

**Step 6:**

To get the ratio identified in Step 5, add coefficients to the formulas which contain the elements whose oxidation number is changing.

As_{2}S_{3} + 2NO^{-}_{3} + H+ → AsO^{3-}_{4} + S + 2NO_{2} + H_{2}O

**Step 7:**

But still the equation is not balanced. Balance the rest of the equation by inspection.

First balance the oxygen. So the balanced equation is,

As_{2}S_{3} + 10NO^{-}_{3} + 4H^{+} → 2AsO^{3-}_{4} + 3S + 10NO_{2} + 2H_{2}O