Question

Construct a table that shows the common oxidation numbers for nitrogen. Deduce in which column the following environmentally important compounds belong: \(\mathrm{HNO}_{2}, \mathrm{NO}, \mathrm{NH}_{3}, \mathrm{~N}_{2} \mathrm{O}, \mathrm{N}_{2}\), \(\mathrm{HNO}_{3}, \mathrm{NO}_{3}{ }^{-}\). Which of the species become prevalent in aerobic conditions in a lake? Under anaerobic conditions? What is the oxidation number of nitrogen in \(\mathrm{NH}_{2} \mathrm{OH}\) ?

Short answer

Nitrogen's oxidation numbers range from -3 to +5. Aerobic conditions favor \(\mathrm{NO}_3^-\) and \(\mathrm{HNO}_3\); anaerobic favor \(\mathrm{NH}_3\) and \(\mathrm{N}_2\). In \(\mathrm{NH}_2\mathrm{OH}\), nitrogen's oxidation number is -1.

Step-by-step solution

Understand Nitrogen's Oxidation States

Nitrogen can exhibit a variety of oxidation states, ranging from -3 to +5, due to its ability to form multiple covalent bonds. The common oxidation states for nitrogen are: -3, -2, -1, 0, +1, +2, +3, +4, and +5.

Assign Oxidation Numbers

Assign oxidation numbers to each nitrogen compound using the rules for oxidation states: - \(\mathrm{HNO}_2\): The oxidation number of nitrogen is +3.- \(\mathrm{NO}\): The oxidation number of nitrogen is +2.- \(\mathrm{NH}_3\): The oxidation number of nitrogen is -3.- \(\mathrm{N}_2\mathrm{O}\): The oxidation number of nitrogen is +1.- \(\mathrm{N}_2\): The oxidation number of nitrogen is 0.- \(\mathrm{HNO}_3\): The oxidation number of nitrogen is +5.- \(\mathrm{NO}_3^-\): The oxidation number of nitrogen is +5.

Construct Oxidation Table

Create a table with the oxidation states of nitrogen. Include each compound with its corresponding oxidation number.| Compound | Oxidation Number of N ||---------------|-----------------------|| \(\mathrm{NH}_3\) | -3 || \(\mathrm{N}_2\) | 0 || \(\mathrm{N}_2\mathrm{O}\) | +1 || \(\mathrm{NO}\) | +2 || \(\mathrm{HNO}_2\) | +3 || \(\mathrm{HNO}_3\) | +5 || \(\mathrm{NO}_3^-\) | +5 |

Identify Aerobic vs Anaerobic Conditions

Aerobic conditions, which involve the presence of oxygen, favor compounds with higher oxidation numbers, such as nitrates. Anaerobic conditions, without oxygen, favor compounds with lower oxidation numbers. - Aerobic prevalent species: \(\mathrm{NO}_3^-\), \(\mathrm{HNO}_3\).- Anaerobic prevalent species: \(\mathrm{NH}_3\), \(\mathrm{N}_2\).

Determine Oxidation Number for NH2OH

For \(\mathrm{NH}_2\mathrm{OH}\) (hydroxylamine), the sum of the oxidation numbers must equal the charge of the compound, which is 0. Assign hydrogen as +1 and oxygen as -2. Let the oxidation number of nitrogen be \(x\):\[x + 2(+1) + (-2) + 1 = 0\]Simplify to find:\[x + 1 = 0\] \[x = -1\] Thus, the oxidation number of nitrogen in \(\mathrm{NH}_2\mathrm{OH}\) is -1.

Key concepts

Environmental Chemistry

Environmental chemistry is the study of chemical processes occurring in the environment. It examines the impact of human activities and natural phenomena on the environment.
Through this lens, the behavior and characteristics of nitrogen compounds are of particular interest.
Nitrogen plays a crucial role in ecosystems, aiding in plant growth and impacting the global nitrogen cycle.

• Different nitrogen compounds display varying levels of reactivity and environmental impact.
• Understanding oxidation states helps predict how nitrogen compounds interact with other elements.
Nitrogen Cycling in the Environment
The nitrogen cycle includes critical processes such as nitrogen fixation, nitrification, denitrification, and ammonification. These processes determine the forms in which nitrogen exists, ranging from ammonium ( ext{NH}_4^+), nitrate ( ext{NO}_3^-), to atmospheric nitrogen ( ext{N}_2).
Effective environmental management requires knowledge of how these compounds contribute to environmental issues like eutrophication and acid rain.

Aerobic Conditions

In aerobic conditions, oxygen is abundant and acts as an electron acceptor in biochemical reactions. This environment influences the nitrogen compounds that prevail in such settings.
High oxidation number nitrogen compounds, like ext{NO}_3^- (nitrates), are more prevalent.

• Aerobic bacteria favor converting ammonium and other nitrogen species to nitrates.
• Processes like nitrification dominate, converting ext{NH}_3 o ext{NO}_2^- and then to ext{NO}_3^-.

Nitrogen Compounds in Aerobic Conditions
Nitrification requires oxygen and yields nitrate, a stable form of nitrogen in well-aerated soils and waters, playing a critical role in the nitrogen cycle. This process significantly affects water quality by contributing to nitrate-rich runoff.
Understanding these dynamics aids in managing agricultural runoff and algal bloom prevention.

Anaerobic Conditions

Anaerobic conditions occur in environments lacking oxygen. This significantly alters which nitrogen species are stable and active. Here, nitrogen compounds with lower oxidation numbers, such as ammonia ( ext{NH}_3), are prevalent.

• Anaerobic environments foster processes like denitrification, where nitrates are reduced back to gaseous forms like ext{N}_2 or ext{N}_2O.
• This process is essential for removing excess nitrates from water bodies.

Nitrogen Compounds in Anaerobic Conditions
In the absence of oxygen, microbes use nitrates as an electron acceptor, converting them to dinitrogen gas ( ext{N}_2) or nitrous oxide ( ext{N}_2O), which are released from the soil.
These conditions help mitigate nitrate pollution by reducing their concentration, impacting greenhouse gas emissions through nitrous oxide release.

Oxidation Numbers in Compounds

The oxidation number of an element in a compound represents its degree of oxidation or loss of electrons. For nitrogen, common oxidation states range from -3 to +5.

• Assign oxidation numbers by using rules: Oxygen typically is -2, and hydrogen is +1. The sum of all oxidation numbers in a neutral compound is zero.
• For ions, the sum equals the charge of the ion.

Determining Nitrogen's Oxidation Numbers
For example, in ext{NH}_3, nitrogen has an oxidation number of -3 due to its three bonds with hydrogen. In nitrates like ext{NO}_3^-, nitrogen is at a +5 oxidation state.
This knowledge allows prediction of how nitrogen compounds behave in different environmental settings and their roles in biochemical cycles.