Question

The oxidation number of nitrogen atoms in \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) are: (a) \(+3,+3\) (b) \(+3,-3\) (c) \(-3,+5\) (d) \(-5,+3\)

Short answer

The oxidation numbers of nitrogen in NH4NO3 are -3 for the NH4+ ion and +5 for the NO3- ion, so the correct answer is option (c).

Step-by-step solution

Understanding the concept of oxidation numbers

The oxidation number or oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. It is defined as the charge that atom would have if the compound was composed of ions.

Applying the rules to NH4+

In the ammonium ion, NH4+, hydrogen has an oxidation number of +1. Since the overall charge of the ion is +1 and there are four hydrogens, nitrogen must balance the charge. The oxidation number of nitrogen can be found using the equation: Oxidation state of nitrogen (N) + 4(oxidation state of hydrogen (H)) = charge of the ion, which is 0 in neutral compounds but +1 here for the ammonium ion. This equation simplifies to N + 4(+1) = +1, which gives N = -3.

Applying the rules to NO3-

In the nitrate ion, NO3-, oxygen has a typical oxidation number of -2. Since the overall charge of the ion is -1 and there are three oxygens, nitrogen’s oxidation number must balance the charge. The formula for this is: Oxidation state of nitrogen (N) + 3(oxidation state of oxygen (O)) = charge of the ion. This simplifies to N + 3(-2) = -1, which gives N = +5.

Deduce the oxidation number of nitrogen atoms in NH4NO3

By combining the results from step 2 and step 3, we can see that the oxidation numbers of nitrogen in NH4NO3 are -3 for the nitrogen in NH4+ and +5 for the nitrogen in NO3-. Therefore, option (c) is the correct answer.

Key concepts

Oxidation State Determination

Oxidation state determination is essential in understanding redox reactions, and this concept serves as the backbone for many principles in chemistry. In simple terms, oxidation state reflects the number of electrons an atom gains or loses when it forms a chemical bond. We assign positive or negative values to indicate whether electrons are lost or gained, respectively. It's like a 'bookkeeping' system to track electron movement in chemical reactions.

To determine oxidation states, a set of rules is followed. Firstly, the oxidation state of a pure element is always zero. Secondly, in compounds or ions, more electronegative elements are assigned negative oxidation states, while less electronegative elements have positive values. For example, in a water molecule (H_{2}O), oxygen is more electronegative and has an oxidation state of -2, while hydrogen has an oxidation state of +1.

Understanding these rules enables students to dissect compounds like NH_{4}NO_{3} and analyze their redox behavior, as they can identify which atoms undergo oxidation or reduction. As illustrated in the step by step solution, nitrogen has different oxidation states in ammonium and nitrate ions, which can be calculated by recognizing the typical oxidation state of hydrogen (+1) and oxygen (-2), and accounting for the overall charge on the ion.

Redox Reactions in Chemistry

Redox reactions, short for reduction-oxidation reactions, are chemical processes where oxidation states change due to electron transfer. These reactions are categorized as redox because they involve both reduction (gain of electrons) and oxidation (loss of electrons). In the context of the exercise, we see nitrogen atoms in different oxidation states indicating that a redox process can occur within the compound.

During a redox reaction, the substance undergoing oxidation will increase in oxidation number, and the substance undergoing reduction will decrease in oxidation number. This interplay is crucial for energy transfer in biological systems, corrosion, electrochemistry, and many industrial processes. A helpful mnemonic to remember is 'OIL RIG' — Oxidation Is Loss, Reduction Is Gain. By analyzing the oxidation states in various components of a chemical reaction, one can predict which species will be oxidized and which will be reduced, thus revealing the direction and the nature of the reaction.

Chemical Compound Nomenclature

The naming of chemical compounds, known as nomenclature, is a systematic method of assigning a unique chemical name to each compound. This system is essential for scientific communication, as it provides a clear and standardized language for describing the composition of compounds. For instance, the compound NH_{4}NO_{3} is named ammonium nitrate, which tells us it contains ammonium (NH_{4}^{+}) and nitrate (NO_{3}^{-}) ions.

Nomenclature uses specific rules set by the International Union of Pure and Applied Chemistry (IUPAC). These include naming ionic compounds by citing the cation first followed by the anion, as seen in sodium chloride (NaCl), or using prefixes for molecular compounds to indicate the number of atoms of each element present in the compound, as in carbon dioxide (CO_{2}). Correct nomenclature enables chemists to infer the possible interactions between different compounds, their structure, and molecular geometry, which provides fundamentals to understanding complex chemical reactions and interactions.