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What is the Difference Between Ammonia and Ammonium?
When discussing water quality, ammonia and ammonium are two terms that cannot be ignored. Although they both contain nitrogen, they exhibit completely different characteristics in water and have vastly different effects on the aquatic environment and human health. A thorough understanding of the differences between the two can help us better monitor and improve water quality.
Ammonia or Ammonium: Key Structural Differences
The chemical formula for ammonia is NH₃. It is a neutral molecule consisting of one nitrogen atom and three hydrogen atoms, with a triangular pyramidal molecular structure.
Ammonium is NH₄⁺. It carries a positive charge and has four hydrogen atom, with a tetrahedral structure.
This structural difference directly causes them to behave differently in water.
Ammonia Or Ammonium: Water Solubility Explained
NH₃ is highly soluble in water, but its solubility decreases as the temperature rises. In water, it mainly exists in a free state, with some undergoing weak reactions with water.
WhileNH₄⁺ is in an ionic state and is more stable in water. It easily combines with other anions in water to form various ammonium salts.
The two can be converted into each other in water, with pH being the key influencing factor.
Primary Transformation Equation
Acid-base equilibrium reaction between ammonia (NH₃) and ammonium ion (NH₄⁺) in water
Note: The ratio of NH₃ to NH₄⁺ depends on the pH of the aqueous solution. When water is alkaline (pH > 7), NH₃ is the main form. At this time, its toxicity is significantly enhanced.In an acidic environment (pH < 7), NH₄⁺ dominates. In this state, its toxicity is greatly reduced.For every unit change in pH value, the ratio between the two changes significantly.
Effect of pH on NH₃/NH₄⁺ Ratio
| pH Value | NH₃ Percentage | NH₄⁺ Percentage |
|---|---|---|
| 6.0 | Approx. 0.4% | Approx. 99.6% |
| 7.0 | Approx. 3.6% | Approx. 96.4% |
| 8.0 | Approx. 27% | Approx. 73% |
| 9.0 | Approx. 80% | Approx. 20% |
| 9.25 (pKa) | 50% | 50% |
| 10.0 | Approx. 94% | Approx. 6% |
Environmental Significance
The NH₃/NH₄⁺ ratio has important implications for aquatic ecosystems. Unionized NH₃ is more toxic to aquatic life, while the ion NH₄⁺ is less toxic. Therefore, in water quality assessment, both total ammonia nitrogen concentration and pH value must be considered.
Related Reactions
Acid dissociation of NH₄⁺
Reaction of NH₃ with acid to form ammonium salt
Release of NH₃ gas from ammonium salt with base
Applications: These reactions have important applications in wastewater treatment, agricultural fertilization, and aquaculture. Controlling pH can adjust the NH₃/NH₄⁺ ratio, thereby reducing toxicity to aquatic organisms or promoting NH₃ removal.
Ammonia Or Ammonium: Aquatic Toxicity Differences
NH₃ is extremely toxic to aquatic organisms such as fish and shrimp. Even at very low concentrations, it can damage their gill tissue and impair respiratory function.
NH₄⁺ has relatively low toxicity. At normal concentrations, it can even be absorbed and utilized by aquatic plants as a nutrient source.
Many aquaculture accidents are associated with sudden increases in ammonia concentrations in water.
Differences in detection methods
Tranditionally detecting NH₃ usually requires the use of special reagents, which are used to determine the concentration through a color reaction with the reagent.
NH₄⁺ can be detected using ion-selective electrode methods to directly measure its ion concentration.
In actual detection, it is often necessary to measure the total amount of both substances and then combine the pH value to analyze their respective proportions.
Removal methods in water treatment
A common method for removing NH₃ from water is aeration. This involves introducing air into the water to allow the NH₃ to escape in gaseous form.
For NH₄⁺ , ion exchange can be used. Resin is used to adsorb ammonium ions from the water to achieve the desired removal.
Biological treatment technology can also effectively reduce the content of both substances by converting them into harmless substances through microbial metabolism.
Relevance to human health
Long-term consumption of water containing high concentrations of NH₃ can irritate the respiratory and digestive tracts.
Although NH₄⁺ poses little direct harm to humans, its presence in water may indicate agricultural pollution of the water source, necessitating further testing for other pollutants.
Controlling the levels of both substances is an important part of ensuring the safety of drinking water during the tap water treatment process.
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Comprehensive guide comparing Ammonia vs Ammonium differences in toxicity, chemical structure, and environmental impact. Essential reading for understanding water chemistry and aquatic safety