Ammonium sulfate is an inorganic salt that provides two necessary nutrients for plant growth. The compound is formed from the reaction between ammonia and sulfuric acid. It is a highly soluble substance. The chemical formula for this compound is written as (NH4)2SO4.
The Chemical Definition and Formula
The formula (NH4)2SO4 represents an ionic compound composed of two distinct polyatomic ions. The compound consists of the ammonium cation, NH4+, and the sulfate anion, SO4^2-. The ammonium ion is positively charged with a +1 valence, while the sulfate ion carries a negative charge of -2.
The subscript 2 indicates that two ammonium ions are required to bond with a single sulfate ion. This ratio is necessary to achieve electrical neutrality, ensuring the total positive charge balances the total negative charge. The molar mass of the compound is approximately 132.14 grams per mole.
High solubility allows the compound to readily dissociate into its constituent ions when dissolved. The compound is odorless. Its aqueous solution tends to be slightly acidic, typically exhibiting a pH between 5 and 6.
Practical Applications
As a fertilizer, it delivers both nitrogen (N) and sulfur (S) to the soil. It contains approximately 21% nitrogen, provided in the readily available ammonium form, and 24% sulfur, present as sulfate. This dual nutrient delivery makes it valuable for crops with high sulfur requirements, such as oilseeds and cruciferous vegetables.
Once applied to the soil, the ammonium ion (NH4+) undergoes a natural process called nitrification, carried out by soil bacteria. During this microbial conversion of ammonium to nitrate, hydrogen ions (H+) are released into the environment. The release of these hydrogen ions has the effect of lowering the soil’s pH balance, which is beneficial for alkaline soils.
This acidifying effect makes the compound a suitable choice for growing acid-loving plants, such as blueberries and rhododendrons. By lowering the pH, the fertilizer increases the availability of certain micronutrients, like iron and manganese, that are often less soluble in alkaline conditions. The compound also serves as an additive in various non-agricultural industries.
Ammonium sulfate is recognized as a food additive, designated as E517, where it functions as an acidity regulator and dough conditioner in baked goods. It is also incorporated into fire retardant mixtures, acting to increase the combustion temperature and promote the formation of char. The compound is also used in biochemistry for the process of protein purification.