# What is the Oxidation Number of Water and How to Determine It

Water's oxidation number indicates its charge in compounds. By following rules, we can find it and understand its chemical role.

Sarah Taylor-

Published on 2023-06-07

## Introduction

Understanding oxidation numbers is crucial in chemistry as they help us identify the distribution of electrons in chemical compounds and reactions. While many compounds have straightforward oxidation numbers, determining the oxidation number for certain molecules, such as water, can be a bit more complex. In this article, we will explore the oxidation number of water and discuss the methods to find it.

## What is the Oxidation Number?

The oxidation number, also known as the oxidation state, of an atom in a compound represents the hypothetical charge that an atom would possess if all its bonds to atoms of different elements were purely ionic. Oxidation numbers are used to track the electron transfer in redox reactions, where oxidation refers to the loss of electrons, and reduction refers to the gain of electrons.

### Oxidation Number of Water:

Water, chemically represented as H2O, is a simple yet essential compound that covers a vast portion of our planet. To determine the oxidation number of water, we must first identify the atoms involved in the molecule. In water, we have two hydrogen atoms (H) bonded to one oxygen atom (O).

Hydrogen typically has an oxidation number of +1 when it forms compounds, while oxygen usually has an oxidation number of -2. However, in some cases, the oxidation number of oxygen can vary. To determine the oxidation number for hydrogen in water, we can assign it as +1, as it usually has this value.

On the other hand, we need to calculate the oxidation number for oxygen. Since we have two hydrogen atoms, each with an oxidation number of +1, the overall charge contributed by hydrogen is +2. Considering the compound as a whole is electrically neutral, the oxidation number of oxygen in water can be calculated using the formula:

Oxidation number of oxygen + (Oxidation number of hydrogen × Number of hydrogen atoms) = 0

Let's substitute the values into the equation:

Oxidation number of oxygen + (+1 × 2) = 0

Oxidation number of oxygen + 2 = 0

By rearranging the equation, we can determine the oxidation number of oxygen:

Oxidation number of oxygen = -2

Therefore, in water (H2O), hydrogen has an oxidation number of +1, and oxygen has an oxidation number of -2.

## How to Find the Oxidation Number of Water

Now that we know the oxidation number for each element in water, let's discuss the steps to find it.

Step 1: Identify the elements present in the compound. In the case of water, we have hydrogen (H) and oxygen (O).

Step 2: Determine the usual oxidation number for each element based on the periodic table. Hydrogen typically has an oxidation number of +1, while oxygen usually has an oxidation number of -2.

Step 3: Assign the oxidation number for hydrogen as +1.

Step 4: Use the equation mentioned earlier to calculate the oxidation number for oxygen:

Oxidation number of oxygen + (Oxidation number of hydrogen × Number of hydrogen atoms) = 0

Step 5: Solve the equation to find the oxidation number for oxygen.

By following these steps, you can determine the oxidation number for water or any other compound that consists of hydrogen and oxygen atoms.

## Conclusion

In summary, the oxidation number of water, H2O, can be determined by understanding the typical oxidation numbers for hydrogen and oxygen. Hydrogen is usually assigned an oxidation number of +1, while oxygen typically has an oxidation number of -2. By using the equation that accounts for the overall charge neutrality of the compound, we can calculate the oxidation number of oxygen

in water, which is -2. Being able to determine the oxidation number of water is important for comprehending its chemical behavior and its role in various reactions.