Problem 7 - Chemistry Matter and Change

Question

Determine the oxidation number of nitrogen in each of these molecules or ions. a. \({NH}_{3}\) b. \({KCN}\) c. \({N}_{2} {H}_{4}\)

Step-by-Step Solution

Answer

The oxidation number of nitrogen in the given molecules or ions is as follows: a. In \(NH_3\), the oxidation number of nitrogen is -3. b. In \(KCN\), the oxidation number of nitrogen is -3. c. In \(N_2H_4\), the oxidation number of nitrogen is -2.

Step 1: Determine the oxidation number of nitrogen in \({NH}_{3}\)

In ammonia, \({NH}_{3}\), nitrogen (\(N\)) is bonded to three hydrogen (\(H\)) atoms. The oxidation state of hydrogen is +1. Since the molecule is neutral, the sum of oxidation states should equal to 0. \(x + 3(1) = 0\) Solve for x, \(x = -3\) Therefore, the oxidation number of nitrogen in \({NH}_{3}\) is -3.

Step 2: Determine the oxidation number of nitrogen in \({KCN}\)

In potassium cyanide, \({KCN}\), the compound is composed of potassium (\(K\)), carbon (\(C\)), and nitrogen (\(N\)). The oxidation state of potassium is +1, and for carbon in a cyanide ion is usually +2 due to its triple bond with nitrogen. The sum of oxidation states in the neutral \({KCN}\) compound should equal to 0. \((1) + 2 + x = 0\) Solve for x, \(x = -3\) Therefore, the oxidation number of nitrogen in \({KCN}\) is -3.

Step 3: Determine the oxidation number of nitrogen in \({N}_{2} {H}_{4}\)

In hydrazine, \({N}_{2} {H}_{4}\), two nitrogen (\(N\)) atoms are bonded to four hydrogen (\(H\)) atoms. The oxidation state of hydrogen is +1. Since the molecule is neutral, the sum of oxidation states should equal to 0. Let x be the oxidation number of each nitrogen atom, since they are the same in this molecule. \(2x + 4(1) = 0\) Solve for x, \(2x = -4\) \(x = -2\) Therefore, the oxidation number of nitrogen in each nitrogen atom in \({N}_{2} {H}_{4}\) is -2.

Key Concepts

Oxidation State

The oxidation state, often referred to as the oxidation number, is a concept in chemistry that describes the degree of oxidation of an atom in a chemical compound. It signifies the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Determining the oxidation state is crucial in understanding the transfer of electrons during chemical reactions. For instance, in the problem above, figuring out the oxidation numbers of nitrogen in

• Ammonia (\({NH}_{3}\))
• Potassium cyanide (\({KCN}\))
• Hydrazine (\({N}_{2}{H}_{4}\))

is an essential step to predict how these substances will behave in redox reactions. The oxidation state helps chemists decide whether a reaction involves reduction or oxidation of the substance.

Chemical Bonding

Chemical bonding involves the interaction between atoms or ions that leads to the formation of molecules or compounds. These bonds determine the structure and chemical properties of compounds. There are several types of chemical bonds:

• Ionic Bonds: Formed when electrons are transferred from one atom to another, leading to positive and negative ions attracting each other.
• Covalent Bonds: Result when atoms share one or more pairs of electrons, as seen in ammonia (\({NH}_{3}\)) and hydrazine (\({N}_{2}{H}_{4}\)).
• Metallic Bonds: Ideal in metals, where electrons form a "sea" of free-moving electrons around positively charged atoms.

Understanding chemical bonding is fundamental in analyzing oxidation states, as the type and arrangement of bonds can influence the theoretical charges on atoms.

Neutral Compounds

Neutral compounds are substances where the overall charge is zero. This neutrality occurs because the sum of all oxidation states in the compound equates to zero. It's a crucial factor in determining individual oxidation states, as seen in \({NH}_{3}\), \({KCN}\), and \({N}_{2}{H}_{4}\).In a neutral compound:

• The sum of all positive charges must balance the sum of all negative charges.
• Though individual atoms within the compound can have non-zero oxidation states, their algebraic sum must equal zero.

This principle was applied in determining the oxidation numbers in the given exercise, facilitating the depletion of algebraic expressions to assign oxidation states.

Ammonia

Ammonia, represented as \({NH}_{3}\), is a compound consisting of one nitrogen atom and three hydrogen atoms. It's an essential chemical in many industrial applications and biological processes. In ammonia:

• Nitrogen typically exhibits an oxidation state of -3.
• Each hydrogen atom has an oxidation state of +1.

Since the molecule is neutral, the sum of these oxidation states gives:\[x + 3(1) = 0\]Solving yields \(x = -3\), confirming nitrogen's oxidation state in ammonia.

Potassium Cyanide

Potassium cyanide (\({KCN}\)) is an example of a compound containing both ionic and covalent bonding characteristics. Composed of potassium, carbon, and nitrogen:

• Potassium (K) has an oxidation state of +1, forming an ionic bond with the cyanide ion.
• Within the cyanide ion, carbon is typically more electropositive and given an oxidation state of +2.

In solving for nitrogen's oxidation state:\[1 + 2 + x = 0\]This results in \(x = -3\), making nitrogen's oxidation number -3 within potassium cyanide.

Hydrazine

Hydrazine (\({N}_{2}{H}_{4}\)) is a simple compound with significant applications as a propellant and a reagent. In hydrazine:

• It contains two nitrogen atoms and four hydrogen atoms.
• All hydrogens are bonded to nitrogens, each bearing an oxidation state of +1.

Letting \(x\) be the oxidation number of each nitrogen, the neutral molecule mandates:\[2x + 4(1) = 0\]Solving gives \(x = -2\), thus each nitrogen atom in hydrazine possesses an oxidation state of -2.