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Sulphate [SO4(2-)]

What Is Sulphate?

Sulphate (SO42-) is one of the most widely available chemical compounds accessible as naturally occurring minerals on earth. It is mostly found in the environment as a result of atmospheric and terrestrial processes. The major contributors of sulphate are sulphur released from the erosion of evaporite deposits, sulphide-containing rocks and minerals and even volcanoes.

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⇒ Sulphate Ion Formula: SO42-

Sulphate is basically a chemical compound that is composed of sulphur and oxygen atoms. Sulphate forms salts with a variety of elements, including potassium, sodium, calcium, magnesium and barium.

Table of Contents

In Chemistry, sulphate or sulfate is considered an inorganic ion or polyatomic anion. Generally, sulfates are the salts or esters of sulphuric acid. It is obtained by deprotonation of both OH groups of sulfuric acid. Additionally, it is an acid derivative for different metals.

IUPAC Name Sulfate
Chemical Formula SO42-
Molar Mass 96.06 g·mol-1
Boiling Point 623.89 °C
Melting Point 270.47 °C

Sulphate Structure [SO42-]

Let us begin by understanding the chemical bonding and molecular structure of sulfate. The sulphate ion is mainly composed of sulphur and oxygen atoms. Here, sulphur is the central atom, and it is surrounded by four oxygen atoms that are located at equal distances in the plane. For the bonding, 2 of the oxygen atoms form S=O bonds and the other two form S-O- bonds. The oxygen atoms are responsible for the negative charge (-2) of the anion because they are in a -2 state.

If we look at the structure or the shape of the molecule, it has a tetrahedral geometry which is further based on the VSEPR theory. In simple terms, sulphate ion has a star-shaped geometry. It is represented as follows:

Sulphate Ion

Structure of Sulphate

The atoms are placed at a 109.5° angle. In order to understand the structure, students can learn to draw the Lewis structure of sulfate and also know about the formal charges and the total number of valence electrons needed for sulfate.

Properties of Sulphate

We will discuss some of the physical and chemical properties of sulphate ions below.

Physical Properties of SO4

  • Ionic sulfates are easily soluble in water. Some of the exceptions are strontium sulfate, calcium sulfate, barium sulfate and lead (II) sulphate. They have low solubility.
  • They tend to form white precipitate during reactions.

Chemical Properties of SO4

A unique chemical property of sulfate is that it can easily link with metals. To expand it further, the oxygen atoms in sulphate ion acts as ligands (arms) and have a tendency to attract the metal to form a bridge or connection. This connection of a chemical compound bonding with metal is called a chelate.

The sulfate ion acts as a ligand, connecting either by two oxygens or single oxygen as a bridge. Nonetheless, sulfate has so many electrons, and it can use any pair of electrons to connect with a metal.

For example, let’s take a neutral metal PtSO4, wherein the sulfate ion acts as a bidentate ligand. The metal-oxygen bonds consist of a particular covalent character in complexes of sulphate.

The sulphate ion is a conjugate base of the bisulfate ion, HSO-4 (hydrogen sulfate) and a conjugate base of sulfuric acid, H2SO4. On the other hand, organic esters of sulfate, like dimethyl sulfate, come under esters of sulfuric acid and covalent compounds.

Preparation of Sulphate

There are usually two methods to prepare sulfates.

  • Oxidation of metal sulphites and sulphides. However, the formation of sulphate as the final state of oxidation may be determined by consecutive reactions, which are critically dependent on other factors such as the catalyst, etc.
  • Treating metal hydroxide, metal oxide and pure metal with sulfuric acid. Some examples include,

Ba(ClO3)2 + H2SO4 → 2 HClO3 + BaSO4

Zn + H2SO4 → ZnSO4 + H2

Cu(OH)2 + H2SO4 → CuSO4 + 2 H2O

One thing to keep in mind during the preparation of sulphate is that sulfuric acid should be deprotonated twice. If it occurs only once, then a hydrogen sulfate ion is made.

Sulphate Examples

Here are some popular examples of sulphates.

Uses of Sulphate

Sulfates are widely available in nature and also easily synthesised in industries. Therefore, this chemical compound has applications in a wide variety of instances. Some of them are listed below.

  • Magnesium sulfate is used in therapeutic baths.
  • Sulphate minerals are used in the preparation of metal salts.
  • Copper sulfate is the most common algaecide.
  • They are used in detergents, emulsifiers, and foaming agents.
  • Gypsum is a natural form of hydrated calcium sulfate used in the making of plasters.
  • Sulfate compounds are also found in many personal care products such as toothpaste, body sprays, lotions, make-up, soaps, shampoos etc.
  • They are used in construction.
  • They are powerful surfactants and are found in most products that are used to remove grease from heavy machinery.
  • Copper sulphate is used in the electricity domain, and barium sulphate is commonly used in water treatment.
  • Sulphates are also added to various products to make them more effective cleaners.

Sulphate Effects and Hazards

The hazards and health effects most likely depend on the type of sulphate.  However, some of the common ones are listed below:

  • Naturally, sulfates can occur as microscopic particles (aerosols), which are a result of fossil fuel and biomass combustion. This can lead to an increase in the acidity of the atmosphere and the formation of acid rain.
  • Effects of sulfates on humans: Shampoos containing sulfate can cause dryness of the scalp, ruin hair cuticles, and usually leave the hair with a negative charge.
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