Question

Which ordering of compounds is according to the decreasing order of the oxidation state on nitrogen ? (a) \(\mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{N}_{2}\) (b) \(\mathrm{HNO}_{3}, \mathrm{NO}, \mathrm{N}_{2}, \mathrm{NH}_{4} \mathrm{Cl}\) (c) \(\mathrm{HNO}_{3}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{NO}, \mathrm{N}_{2}\) (d) \(\mathrm{NO}, \mathrm{HNO}_{3}, \mathrm{NH}_{4} \mathrm{Cl}, \mathrm{N}_{2}\)

Short answer

The correct ordering according to the decreasing oxidation state of nitrogen is HNO3, NO, N2, NH4Cl, which corresponds to option (b).

Step-by-step solution

Identify the Oxidation State of Nitrogen in HNO3

In HNO3, nitrogen is bonded with three oxygen atoms and one hydrogen atom. Oxygen generally has an oxidation state of -2 and hydrogen has +1. Using the formula x + (-2)*3 + 1 = 0 (because the compound is neutral), solving for nitrogen's oxidation state x gives x = +5.

Identify the Oxidation State of Nitrogen in NO

In NO, nitrogen is bonded with one oxygen atom. Oxygen has an oxidation state of -2, therefore for the compound to be neutral, nitrogen must have an oxidation state of +2.

Identify the Oxidation State of Nitrogen in NH4Cl

In NH4Cl, NH4 is the ammonium ion with a +1 charge and Cl is the chloride ion with a -1 charge. Nitrogen, in this case, shares its electrons with 4 hydrogen atoms, each contributing +1 to the oxidation state. Therefore, nitrogen has an oxidation state of -3.

Identify the Oxidation State of Nitrogen in N2

In N2, nitrogen is in its elemental form, and the oxidation state of an element in its standard state is 0.

Arrange the Compounds in Decreasing Order of Oxidation State of Nitrogen

Now that we have the oxidation states for nitrogen in all the compounds: HNO3 (+5), NO (+2), NH4Cl (-3), N2 (0), the decreasing order is: HNO3 > NO > N2 > NH4Cl.

Key concepts

Oxidation State Determination

Understanding oxidation states, also known as oxidation numbers, is crucial when studying chemical reactions. An oxidation state is a number assigned to an element in a chemical compound that represents the number of electrons lost or gained by an atom of that element in the compound.

The general rules for determining oxidation states include that pure elements have an oxidation state of 0, the sum of oxidation states in a neutral molecule must be 0, and in ions it must equal the charge of the ion. For example, in a molecule of HNO3, hydrogen (H) has an oxidation state of +1, and oxygen (O), typically, has an oxidation state of -2. By calculating the total charge contributed by H and O, the oxidation state of nitrogen (N) is deduced to ensure the overall charge is neutral. With these simple rules, one can assign the correct oxidation states to help understand chemical reactions, especially redox reactions where the change in oxidation states indicates the transfer of electrons.

Chemical Nomenclature

The naming of chemical compounds, known as chemical nomenclature, allows scientists to communicate unambiguously. For example, the compound NH4Cl is named ammonium chloride. 'Ammonium' indicates an NH4+ ion, while 'chloride' refers to the Cl- ion. The correct use of nomenclature not only helps in identifying the composition of the compound but also gives information about the potential bonding and oxidation states of its constituents.

In naming binary compounds like NO, the naming convention often signifies the oxidation state of the elements involved. Nitrogen monoxide (or nitric oxide) informs us that there is one nitrogen atom and one oxygen atom, leading us to infer the oxidation states by understanding that oxygen normally has an oxidation state of -2 and the overall molecule is neutral.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are processes where electrons are transferred between substances. These reactions are often identified by changes in oxidation states. A substance that loses electrons is oxidized, and its oxidation state increases, while a substance that gains electrons is reduced, and its oxidation state decreases.

A classic example can be seen in the reaction between hydrogen and oxygen to form water. In this reaction, the oxidation state of oxygen decreases from 0 to -2, thus it is reduced, while the oxidation state of hydrogen increases from 0 to +1 as it is oxidized. Redox reactions are essential to many biological and industrial processes, including cellular respiration and the operation of batteries.