Question

Indicate the oxidation number of nitrogen in each of the following compounds.

(a) NH3

---

(b) N2H4

---

(c) NF3

---

(d) NH2OH

---

(e) Fe(NO3)3

---

(f) HNO2

Answer 1

Oxidation number: The charge assigned to an atom in a compound is called an oxidation number.

The rules for assigning oxidation number of an element as shown below:

1. The oxidation number of an uncombined element or molecule is taken as .

2. The oxidation number of monoatomic ion is equal to its ionic charge.

3. In a molecule, the higher electronegative element has the oxidation number equal to the charge of that element when it was a monoatomic ion.

4. The oxidation number of hydrogen is but when it is combined with metal, its oxidation number is .

5. Oxygen has an oxidation number of when it forms an oxide, while its oxidation is number is when it forms peroxide .

6. The sum of oxidation number of all the elements in molecules should be equal to zero and for ionic compounds should be equal to its ionic charge. The rule for finding the oxidation state of an element in a molecule is shown below:

…… (1)

(a)

Ammonia contains nitrogen and hydrogen. The molecule is neutral as there is no net charge on the molecule. The nitrogen belongs to group V . Nitrogen is more electronegative than hydrogen, so the nitrogen will have negative oxidation number.

In , there are three hydrogens. So, the total positive oxidation number will be as shown below:

Substitute as net charge and as total positive oxidation number in equation to find the total negative oxidation number of ammonia as shown below:

There is one nitrogen atom in . The oxidation number of nitrogen is calculated as shown below:

Therefore, the oxidation number of nitrogen in is .

(b)

Hydrazine contains nitrogen and hydrogen. The molecule is neutral as there is no net charge on the molecule. The nitrogen belongs to group V . Nitrogen is more electronegative than hydrogen, so the nitrogen will have negative oxidation number.

In , there are four hydrogens. So, the total positive oxidation number will be as shown below:

Substitute as net charge and as total positive oxidation number in equation to find the total negative oxidation number of hydrazine as shown below:

There is two nitrogen atom in . The oxidation number of nitrogen is calculated as shown below:

Therefore, the oxidation number of nitrogen in is .

(c)

Nitrogen trifluoride contains nitrogen and fluorine. The molecule is neutral as there is no net charge on the molecule. The nitrogen belongs to group V and fluorine belongs to group VII So, the oxidation number of fluorine is . Nitrogen is less electronegative than fluorine, so the nitrogen will have positive oxidation number.

In , there is three fluorine atom. So, the total negative oxidation number will be as shown below:

Substitute as net charge and as total negative oxidation number in equation to find the total positive oxidation number of as shown below:

There is one nitrogen atom in . The oxidation number of nitrogen is calculated as shown below:

Therefore, the oxidation number of nitrogen in is .

(d)

Hydroxylamine contains nitrogen, hydrogen, and oxygen. The molecule is neutral as there is no net charge on the molecule. The oxygen belongs to group VI .So, the oxidation number of oxygen is .

In , there is three hydrogen atom. So, the total positive oxidation number will be as shown below:

Substitute as net charge and as total positive oxidation number in equation to find the total negative oxidation number of as shown below:

There is one nitrogen atom and one oxygen atom in . The total negative oxidation number will be equal to the sum of oxidation number of nitrogen and oxygen. The oxidation number of nitrogen is calculated as shown below:

Therefore, the oxidation number of nitrogen in is .

(e)

Iron nitrate is an ionic compound which contains metal ion and polyatomic anion. The metal is iron while nitrate ion is polyatomic ion. The molecule is neutral as there is no net charge on the molecule. The nitrate ion has charge. So, iron will have positive oxidation number.

The nitrate ion contains nitrogen and oxygen. It is ionic as it has charge. The oxygen belongs to group VI .So, oxygen has a charge . So, the total negative oxidation number of nitrate ion will be as shown below:

Substitute as net charge and as total negative oxidation number in equation to find the total positive oxidation number of nitrate ion as shown below:

Therefore, the oxidation number of N in are .

(f)

Nitrous acid contains nitrogen, hydrogen and oxygen. The molecule is neutral as there is no net charge on the molecule. The oxygen belongs to group VI .So, the oxidation number of oxygen is .

In , there is one hydrogen atom. So, the total positive oxidation number will be as shown below:

Substitute as net charge and as total positive oxidation number in equation to find the total negative oxidation number of as shown below:

There is one nitrogen atom and two oxygen atom in . The total negative oxidation number will be equal to the sum of oxidation number of nitrogen and oxygen. The oxidation number of nitrogen is calculated as shown below:

Therefore, the oxidation number of nitrogen in is .