Problem 15 - Chemistry and Chemical Reactivity

Question

A 2010 article in Science magazine described "Sewage Treatment with Anammox." IB. Kartal, I. G. Kuenen, and M. C. M. van Loosdrecht, Science, Vol. \(328,\) pp. \(702-703,2010 .\) The authors noted that "Fixed nitrogen such as ammonium and nitrate [ions] must be removed [from sewage] to avoid toxic algal blooms in the environment." One approach to removing ammonium ions is to use ammonium-oxidizing (anammox) bacteria. Two (unbalanced) reactions that are involved are: $$\begin{array}{l}\mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{NO}_{2}^{-}(\mathrm{aq}) \rightarrow \mathrm{N}_{2}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(\ell) \\\\\mathrm{NH}_{4}^{+}(\mathrm{aq})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow \mathrm{NO}_{2}^{-}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\ell)\end{array}$$ Balance these two equations in acid solution.

Step-by-Step Solution

Answer

The balanced equations are: \(2\mathrm{NH}_4^{+} + \mathrm{NO}_2^{-} \rightarrow \mathrm{N}_2 + 4\mathrm{H}_2\mathrm{O}\) and \(\mathrm{NH}_4^{+} + 1.5\mathrm{O}_2 \rightarrow \mathrm{NO}_2^{-} + 2\mathrm{H}_2\mathrm{O}\).

Step 1: Balance the First Equation

To balance \(\mathrm{NH}_4^{+}(\mathrm{aq})+\mathrm{NO}_2^{-}(\mathrm{aq}) \rightarrow \mathrm{N}_2(\mathrm{g})+\mathrm{H}_2\mathrm{O}(\ell)\), first balance the nitrogen atoms. This requires 2 ammonium ions and 1 nitrite ion to produce 1 nitrogen gas Thus, we write \(2\mathrm{NH}_4^{+}(\mathrm{aq}) + \mathrm{NO}_2^{-}(\mathrm{aq}) \rightarrow \mathrm{N}_2(\mathrm{g}) + 4\mathrm{H}_2\mathrm{O}(\ell)\).

Step 2: Verify Mass and Charge Balance

For the first equation, check that the elements and charges are balanced. There are 2 N atoms, 8 H atoms, and 2 positive charges on the left. On the right, there are 2 N atoms and 8 H atoms in the form of 4 \(\mathrm{H}_2\mathrm{O}\) molecules, balancing both mass and charge.

Step 3: Balance the Second Equation

For \(\mathrm{NH}_4^{+}(\mathrm{aq})+\mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{NO}_2^{-}(\mathrm{aq})+\mathrm{H}_2\mathrm{O}(\ell)\), start by balancing nitrogen, then hydrogen, and oxygen. The equation is balanced as is: \(\mathrm{NH}_4^{+}(\mathrm{aq}) + 1.5\mathrm{O}_2(\mathrm{g}) \rightarrow \mathrm{NO}_2^{-}(\mathrm{aq}) + 2\mathrm{H}_2\mathrm{O}(\ell)\).

Step 4: Verify Mass and Charge Balance Again

In the second equation, confirm the balance. On the left, there is 1 N, 4 H, and 2 O atoms, which match the 1 N, 2 H, and 2 O atoms on the right. Both sides have a net charge of +1. Thus, the elements and charges are balanced.

Key Concepts

Nitrogen Removal

In the realm of environmental chemistry, nitrogen removal is a crucial process. Nitrogen in the form of nitrate (NO₂⁻) and ammonium (NH₄⁺) ions is often found in wastewater from sources like agriculture and sewage. If not efficiently removed, these compounds can enter water bodies and contribute to problems such as toxic algal blooms and harm aquatic life. To combat this, treatments focus on converting these compounds into nitrogen gas (N₂), which is harmless since it makes up the majority of Earth's atmosphere.

One innovative method for achieving nitrogen removal is the Anammox process. This process uses specialized bacteria that can oxidize ammonium directly to nitrogen gas, an efficient shortcut compared with traditional methods. This is not only energy-saving but also reduces the need for additional chemicals. Understanding the chemical reactions involved, including balancing equations, allows environmental scientists to design effective wastewater treatment strategies.

Sewage Treatment

Sewage treatment is an essential part of managing waste in urban environments, ensuring that pollutants do not harm the environment or human health. Modern methods involve several stages, including physical, chemical, and biological processes.

A breakthrough in biological treatment is the use of Anammox bacteria. These bacteria efficiently remove nitrogen compounds from sewage. Unlike conventional methods that require a two-step process for nitrification and denitrification, the Anammox process combines these steps. This not only saves time and costs but reduces greenhouse gas emissions as well.

The successful integration of Anammox in sewage treatment reflects the importance of innovative approaches in environmental management. It is crucial for students to understand how these processes benefit society and the environment.

Chemical Reaction Balancing

Balancing chemical reactions is a fundamental skill in chemistry, crucial for representing chemical processes accurately. In the context of sewage treatment and Anammox, it ensures that all elements are appropriately accounted for, both in terms of mass and charge.

Take the Anammox reactions as an example. The first step in balancing these reactions involves ensuring that nitrogen atoms, hydrogen atoms, and charges are equal on both sides. For instance, in the reaction: \[2\mathrm{NH}_4^{+}(\mathrm{aq}) + \mathrm{NO}_2^{-}(\mathrm{aq}) \rightarrow \mathrm{N}_2(\mathrm{g}) + 4\mathrm{H}_2\mathrm{O}(\ell)\]we have two nitrogen atoms from ammonium and one from nitrite, forming nitrogen gas, along with balancing hydrogens and charges.

By practicing balancing reactions, students can better understand the stoichiometry of chemical processes, vital for fields like environmental chemistry.

Environmental Chemistry

Environmental chemistry is a discipline focused on understanding chemical processes occurring in the environment. It tackles crucial issues, such as pollution control and sustainable resource management.

Nitrogen cycling and removal play a huge role in environmental chemistry. With processes like Anammox, which contribute to decreasing nitrogen pollution, understanding these nitrogen transformations is essential. Anammox is a perfect example of how environmental chemistry directly applies to real-world issues in wastewater management.

Through studying environmental chemistry, students gain insights into the scientific principles that govern natural processes. This knowledge empowers them to develop solutions to ongoing environmental challenges, ensuring a sustainable future for our ecosystems.