Sulphate

What is Sulphate?

Sulphate (Sulfate) is one of the most widely available chemical compounds that are available as naturally occurring minerals on earth. It is mostly found in the environment as a result of atmospheric and terrestrial processes. The major contributors though are sulphur released from erosion of evaporite deposits and sulphide containing rocks and minerals and even volcanoes. 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. In chemistry, sulphate or sulfate is taken to be an inorganic ion or polyatomic anion. Sulphate formula is given as SO42-. Generally, sulfates are also taken to be 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. Explore more about this compound below.

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

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 which are located at equal distances in the plane. As 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 -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 has a start shaped geometry. It is represented as:

Sulphate Ion

Structure of Sulphate

The atoms are placed at 109.5-degree angle. In order to determine the structure students can learn to draw the Lewis structure of sulfate and also know about the formal charges as well as 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 Sulphates

  • 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 Sulphates

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 it will 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, 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 bisulfate ion, HSO-4 (hydrogen sulfate) and a conjugate base of sulfuric acid, H2SO4. Meanwhile, 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 of the 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 hydrogen sulfate ion is made.

Sulphate Examples

Here are some popular examples of sulphates.

  • Sodium Sulphate
  • Calcium Sulphate
  • Copper Sulphate
  • Iron (II) Sulphate
  • Gypsum
  • Magnesium Sulphate
  • Hydrogen Sulphate
  • Lead Sulphate
  • Sodium Lauryl Sulphate

Uses of Sulphate

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

  • Sulphate minerals are used in the preparation of metal salts.
  • Copper sulfate is the most common algaecide.
  • Magnesium sulfate is used in therapeutic baths.
  • Gypsum is a natural form of hydrated calcium sulfate used in making of plasters.
  • They are used in detergents, emulsifiers, and foaming agents.
  • 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 constructions.
  • Copper sulphate in electricity domain and barium sulphate is commonly used in water treatment.
  • Sulphates are also added in various products to make them more effective cleaners. 
  • They are powerful surfactants and are found in most products that are used to remove grease from heavy machinery.

Sulphate Effects and Hazards

The hazards and health effects most likely depend on each sulphate.  However, some of the popular ones are:

  • Naturally, sulfates can occur as microscopic particles (aerosols) which is a result of fossil fuel and biomass combustion. This can lead to an increase in the acidity of the atmosphere and formation of acid rain.
  • As for the effects on humans, it can cause dryness of skin, ruin hair cuticle, and they usually leave the hair with a negative charge.

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