Problem 100 - Chemistry The Science in Context

Question

Give the oxidation number of nitrogen in each of the following: (a) elemental nitrogen \(\left(\mathrm{N}_{2}\right) ;\) (b) hydrazine \(\left(\mathrm{N}_{2} \mathrm{H}_{4}\right) ;(\mathrm{c})\) ammonium ion \(\left(\mathrm{NH}_{4}^{+}\right)\)

Step-by-Step Solution

Answer

Answer: The oxidation number of nitrogen in elemental nitrogen (N2) is 0, in hydrazine (N2H4) is -2, and in ammonium ion (NH4+) is -3.

Step 1: Identify the rules for oxidation numbers

To determine the oxidation number of nitrogen in each compound, we need to remember the following rules: 1. The oxidation number of an element in its uncombined state (elemental form) is always zero. 2. The oxidation number of a monatomic ion equals the charge of the ion. 3. The sum of oxidation numbers of all the atoms in a neutral molecule is equal to zero. 4. The sum of the oxidation numbers of all the atoms in a polyatomic ion is equal to the overall charge of the ion.

Step 2: Determine the oxidation number of nitrogen in elemental nitrogen

In elemental nitrogen \(\left(\mathrm{N}_{2}\right)\), we have nitrogen in its elemental form. According to rule 1, the oxidation number of nitrogen in this compound is zero. Thus, the oxidation number of nitrogen in \(\left(\mathrm{N}_{2}\right)\) is 0.

Step 3: Determine the oxidation number of nitrogen in hydrazine

In hydrazine \(\left(\mathrm{N}_{2}\mathrm{H}_{4}\right)\), we have a neutral molecule. According to rule 3, the sum of oxidation numbers of all the atoms in this molecule is equal to zero. Let the oxidation number of nitrogen be x. We know that the oxidation number of hydrogen is +1. Therefore, we can write: 2x + 4(1) = 0 2x = -4 x = -2 Thus, the oxidation number of nitrogen in hydrazine \(\left(\mathrm{N}_{2}\mathrm{H}_{4}\right)\) is -2.

Step 4: Determine the oxidation number of nitrogen in ammonium ion

In the ammonium ion \(\left(\mathrm{NH}_{4}^{+}\right)\), we have a polyatomic ion with a charge of +1. According to rule 4, the sum of oxidation numbers of all the atoms in this ion is equal to the overall charge, which is +1. Let the oxidation number of nitrogen be x. We know that the oxidation number of hydrogen is +1. Therefore, we can write: x + 4(1) = +1 x = -3 Thus, the oxidation number of nitrogen in the ammonium ion \(\left(\mathrm{NH}_{4}^{+}\right)\) is -3.

Key Concepts

Elemental Nitrogen

Elemental nitrogen is a fascinating molecule that greatly impacts the chemistry of our planet. In its natural state, nitrogen exists as a diatomic molecule, represented as \( \text{N}_2 \). This means two nitrogen atoms are bound together, forming a molecule that is quite stable under standard conditions.

One of the key concepts in understanding elemental nitrogen is recognizing its zero oxidation state. In chemistry, an element in its pure form, like \( \text{N}_2 \), is considered to have an oxidation number of zero. This is because the electrons shared between the two nitrogen atoms are evenly distributed.

Due to this neutral state, elemental nitrogen doesn't easily react with other substances, making it an inert component of the earth's atmosphere. In fact, it makes up about 78% of the air we breathe! Therefore, elemental nitrogen plays a crucial role in both the biological and atmospheric chemistry.

Hydrazine

Hydrazine, represented as \( \text{N}_2\text{H}_4 \), is quite the interesting compound with a variety of practical applications. It consists of two nitrogen atoms and four hydrogen atoms. It is commonly used as a reducing agent in chemical reactions and as a fuel in rocket propulsion.

The oxidation number of nitrogen in hydrazine is distinct because it's not zero, unlike in elemental nitrogen. Here's how you can determine it:

• The molecule is neutral, so the overall oxidation states must sum to zero.
• Hydrogen has an oxidation state of +1.
• Let the oxidation state of nitrogen be \( x \).
• Using the formula \( 2x + 4(1) = 0 \), we solve for \( x \).
• This simplifies to \( 2x = -4 \), thus \( x = -2 \).

Therefore, the oxidation number of nitrogen in hydrazine is -2. This negative oxidation state signifies nitrogen's tendency to gain electrons within the compound, contributing to its energetic and reactive nature.

Ammonium Ion

The ammonium ion, \( \text{NH}_4^+ \), is a crucial player in biological and environmental chemistry. It is a positively charged polyatomic ion that plays a key role in the nitrogen cycle, influencing processes like fertilization and plant growth.

Calculating the oxidation number of nitrogen in an ammonium ion is an excellent exercise in understanding oxidation states in ions. Let's break it down:

• The ion itself has a +1 charge, so the oxidation numbers must add up to +1.
• With hydrogen's oxidation number as +1, we denote nitrogen's oxidation number as \( x \).
• The equation becomes \( x + 4(1) = +1 \).
• Solving this gives \( x = -3 \).

Hence, the oxidation number of nitrogen in the ammonium ion is -3. This value indicates nitrogen’s effective charge amidst its atomic bonds in the ion, highlighting its ability to "hold onto" electrons from the hydrogens.