Question

Arrange the following species in order of increasing oxidation number of the sulfur atom: (a) \(\mathrm{H}_{2} \mathrm{~S}\) (b) \(\mathrm{S}_{8}\) (c) \(\mathrm{H}_{2} \mathrm{SO}_{4}\) (d) \(\mathrm{S}^{2-},(\mathrm{e}) \mathrm{HS}^{-},(\mathrm{f}) \mathrm{SO}_{2},(\mathrm{~g}) \mathrm{SO}_{3}\)

Short answer

So, the species in increasing order of oxidation number of sulfur are: \(S_{8}\) (-2), \(H_{2}S\) (-1), \(HS^{-}\) (+4), \(SO_{2}\) (+6), \(H_{2}SO_{4}\), \(SO_{3}\)

Step-by-step solution

Oxidation Number for H2S

In H2S, Hydrogen has an oxidation number of +1. Since there are two, the total is +2. In order to balance this, Sulphur's oxidation number must be -2.

Oxidation Number for S8

In S8, Sulfur is in its elemental form, so its oxidation number is zero.

Oxidation Number for H2SO4

In H2SO4, Hydrogen's oxidation number is +1 and Oxygen's is -2. Since there are two hydrogen atoms and four oxygen atoms, the total is +2 -8 = -6. To balance this, Sulfur's oxidation number must be +6.

Oxidation Number for S^2-

In S^2-, Sulfur is in the form of an ion. So, its oxidation number is -2, which is equal to its charge.

Oxidation Number for HS^-

In HS^-, Hydrogen's oxidation number is +1. Since the compound is negative, to balance the charge, Sulphur's oxidation number must be -1.

Oxidation Number for SO2

In SO2, Oxygen's oxidation number is -2. Since there are two oxygen atoms, the total is -4. To balance this, Sulphur's oxidation number must be +4.

Oxidation Number for SO3

In SO3, Oxygen's oxidation number is -2. Since there are three oxygen atoms, the total is -6. To balance this, Sulphur's oxidation number must be +6.

Key concepts

Sulfur Compounds

Sulfur compounds are chemical substances that contain sulfur as part of their composition. These compounds have a wide range of applications in different fields, from industry to biology.
Some common examples include hydrogen sulfide (H\(_2\)S), sulfur dioxide (SO\(_2\)), and sulfur trioxide (SO\(_3\)).
Sulfur compounds are categorized based on the oxidation state of sulfur, which influences their chemical behavior and reactivity. For instance:

• Sulfides: These compounds contain sulfur in a lower oxidation state, such as in S\(^{2-}\) and HS\(^{-}\).
• Sulfur Dioxide: Found in the oxidation state +4, and is a common atmospheric pollutant typically formed from burning fossil fuels.
• Sulfuric Acid: In compounds like H\(_2\)SO\(_4\), sulfur has an oxidation state of +6, which is its highest oxidation state and represents a highly oxidized compound.

Understanding sulfur compounds is fundamental in chemistry, especially for processes like combustion, synthesis, and environmental science.

Elemental Sulfur

Elemental sulfur, often represented by S\(_8\), is one of the most stable forms of sulfur under normal conditions.
It is a yellow solid that is odorless and insoluble in water, found naturally in volcanic regions and hot springs.
Elemental sulfur exhibits an oxidation state of zero. This makes it unique, as it represents a balanced state where sulfur is neither gaining nor losing electrons in chemical reactions.

• Commonly used in agriculture as a fungicide and pesticide.
• In industry, it is a vital component in the production of sulfuric acid.
• Elemental sulfur can also be transformed into various allotropes, exhibiting different physical structure properties.

This non-reactive form allows it to be easily stored and transported, making elemental sulfur a versatile and important material in many fields.

Oxidation States

Oxidation states, sometimes referred to as oxidation numbers, are a core concept in understanding sulfur chemistry. They indicate the degree of oxidation of an atom in a compound.
For sulfur, the oxidation states can vary significantly, ranging from -2 in sulfides to +6 in sulfates.
These numbers are essential for determining how sulfur atoms interact with other elements and in predicting the outcomes of chemical reactions.

• Low Oxidation State (-2): Found in compounds like H\(_2\)S and S\(^{2-}\), where sulfur may share electrons or gain them.
• Intermediate Oxidation State (+4): Present in SO\(_2\), which is often a precursor in many chemical reactions, like forming acid rain.
• High Oxidation State (+6): Seen in compounds such as H\(_2\)SO\(_4\) and SO\(_3\), where sulfur is fully oxidized and often in stable, non-reactive compounds.

Understanding and calculating oxidation states are crucial skills in chemistry as they help to balance chemical equations and define the movement of electrons in reactions.