Ammonium is an ion integral to biology, ecological processes, agriculture, industry and human nature. Close to its gaseous parent ammonia (NH3), ammonium is part of nitrogen fixation with its own properties and functions.
Ammonium is a cation or positively charged ion, formed through protonation of ammonia. Ammonia, a weak base, accepts a hydrogen ion (H+) from an acid. The reaction can be represented as:
NH3 (ammonia) + H+ (hydrogen ion) ⇌ NH+4 (ammonium ion)
This process is reversible depending on the pH of the environment. In acidic conditions, the equilibrium shifts towards ammonium formation, while in alkaline conditions, the equilibrium favors ammonia.
Ammonium exists mainly in aqueous environments, integral to many biochemical processes, especially in nitrogen cycling. It's produced in both natural and synthetic ways.
Natural Production: Ammonium occurs naturally when bacteria break down organic matter. For example, in forest ecosystems, decaying leaves release ammonia, which is converted to ammonium, allowing for plant uptake.
Industrial Synthesis: The Haber-Bosch process is the primary industrial method for producing ammonia. In this process, nitrogen from the atmosphere is combined with hydrogen.
The hydrogen is derived from natural gas at high heat and pressure. About 80 million tons of ammonia are produced globally with this method each year.
Waste Processing: In manure or wastewater management, activity by bacteria and fungi convert organic nitrogen from dead organisms back into ammonium Up to 35% of nitrogen in wastewater can end up as ammonium.
Ammonium's tetrahedral structure with nitrogen at the center bonded to four hydrogen atoms gives it a positive charge. This positive charge allows it to form ionic bonds with various negative ions.
These include chloride (Cl-) in ammonium chloride (NH4Cl) or sal ammoniac; and nitrate (NO3-) in ammonium nitrate (NH4NO3). These salts are often water-soluble due to the strong interactions between the ions and water molecules.
Molecular Weight: 18.04 g/mol
Molecular Structure: The ammonium ion consists of one nitrogen atom surrounded by four hydrogen atoms, giving it a tetrahedral shape.
Appearance: Exists only in solution or as part of salts.
Solubility: Ammonium is highly soluble in water, with solubility ranging around 60 g/L at 20°C. This high level of solubility enables its easy absorption by plants and microorganisms.
Acidity: Ammonium itself is a weak acid, capable of donating a proton back to form ammonia.
pH Influence: Ammonium can affect the pH of soil and water. In agriculture and homestead gardens, ensuring optimal pH increases nutrient availability and enhance plant growth.
Reactivity:
Reactivity of ammonium depends on the accompanying anion. Ammonium salts can undergo a variety of reactions, including:
Neutralization Reactions: Reacting with bases to produce ammonia, water, and a salt.
Decomposition Reactions: Heating ammonium salts can decompose them, producing ammonia and other gases.
Oxidation Reactions: Ammonium can be oxidized to form nitrogen oxides.
Formation of Ammonium Salts: Ammonium combines readily with anions to form a range of ammonium salts, used extensively in fertilizers and chemical production. For example, ammonium nitrate (NH4NO3) is a fertilizer delivering nitrogen and ammonium to crops.
Functions in Nature and the Environment
Nitrogen Cycle: Ammonium is an intermediate in the nitrogen cycle. Bacteria in the soil transform atmospheric nitrogen gas to ammonia in the process of nitrogen fixation. Ammonia is then converted to ammonium ions, ready for uptake by plants.
Soil Nutrient: Ammonium in soil acts is an important nutrient for plant growth. Plants absorb ammonium ions and use them to synthesize essential amino acids, proteins and nucleic acids.
Ammonium affects soil fertility and structure. Its retention in the soil can improve nutrient availability by preventing leaching.
Water Bodies: In aquatic ecosystems, ammonium is a significant source of nitrogen for algae and other water plants. Excess ammonium levels from pollution can cause eutrophication, algal blooms and oxygen depletion.
Microbial Activity: Many microorganisms use ammonium as a nitrogen source, driving biological processes like nitrification, where ammonium is oxidized to nitrite and subsequently to nitrate for soil fertility.
Importance as a Nitrogen Source
Ammonium is a readily available and essential nitrogen source for plants. Thus, ammonium-based fertilizers like ammonium nitrate, ammonium sulfate and urea are widely used in agriculture.
These fertilizers provide plants with nitrogen they need to grow and develop. Excess use of fertilizers can lead to environmental problems like water pollution and greenhouse gas emissions such as CO2 or methane.
Nitrogen is vital for all living organisms. It is a key component of amino acids, proteins, and nucleic acids, which are essential for life.
Ammonium is easy to take up by plants. Unlike nitrate, which can leach away, ammonium tends to remain in the soil, making it accessible for crops.
Function in Urine
Ammonium functions in the composition of urine. The kidneys excrete excess acids as ammonium ions, helping maintain the body's pH balance.
When the body produces more acid than it expels, the kidneys can synthesize ammonia. This then combines with hydrogen ions to form ammonium, effectively neutralizing the acid so it can be excreted.
Waste Excretion
Ammonium is formed during amino acid breakdown, detoxifying excess nitrogen. The body excretes this excess in the form of urea or ammonium.
Regulatory Mechanism
In birds and reptiles, nitrogen is primarily excreted as uric acid. During metabolism, uric acid can convert to ammonium. This maintains nitrogen balance in organisms and prevents toxicity.
Other Uses
Beyond agriculture and biology, Ammonium compounds find use in:
Cleaning products: Ammonium hydroxide (a solution of ammonia in water) is a common ingredient in household cleaners.
Textile industry: Used as a mordant, enabling dyes to adhere to fabrics.
Leather tanning: Used in the tanning process to condition hides.
Food Industry: Ammonium bicarbonate is a leavening agent in baking, aiding in dough rise and texture. It's traditionally used as the leavener in some Swedish specialty cookies.
Difference between Ammonia and Ammonium
The key difference lies in the presence of a hydrogen ion (H+). Ammonia (NH3) is a neutral molecule, while ammonium (NH4+) is a positively charged ion.
Ammonia is a gas at room temperature, while ammonium only exists in solution or as part of salts. The presence of the positive charge significantly alters the properties and reactivity of ammonium compared to ammonia.
Although the terms are often used interchangeably, ammonia and ammonium have distinct characteristics: Ammonium is less volatile than ammonia, often favoring its existence in aqueous solutions.
Facts About Ammonium
Discovery: c. 800 AD Islamic alchemist Jabir ibn Hayyan discovers ammonium chloride in the soot from burning camel dung.
Historical Significance: Ammonium has been recognized for centuries; ancient farmers use animal waste to fertilize crops.
Aquatic Toxicity: Concentrations above 0.5 mg/L can kill fish.
Natural Resources: Ammonium sulfates occur as minerals and are used in agriculture and food products.
Lunar Discovery: Ammonium has been detected on the moon.
Early Medical Use: Ammonium is used in early medicine for its antiseptic properties. Quaternary ammonium compounds (QACs) have strong disinfectant properties. They degrade microorganism proteins, target and destroy the plasma membrane or bacterial cell wall.
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