Sulphuric Acid: Formula, Structure, Properties & Uses

STUDY ABOUT OXIDES OF SULPHUR

Sulphuric Acid: Molecular Weight

The molecular formula of sulphuric acid is \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}.\) This formula shows that one molecule of sulphuric acid \(\left( {{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}} \right)\) contains \(2\) moles of hydrogen atoms, \(1\) mole of sulphur and \(4\) moles of oxygen atoms. So, the molecular mass of  \({{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}}\) will be equal to the sum of the masses of \(2\) moles of hydrogen atoms, \(1\) mole of a sulphur atom and \(4\) moles of oxygen atoms. The atomic mass of hydrogen is \(1{\rm{u}},\) the sulphur is \({\rm{32u,}}\) and that of oxygen is \({\rm{16u,}}\) the molecular mass of sulphuric acid can be calculated as follows:

Molecular mass of \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} = \) Mass of \(2\) moles of hydrogen atoms \(+\) Mass of \(1\) mole of sulphur \(+\) Mass of \(4\) moles of oxygen atoms
\(= 2 \times 1 + 32 + 4 \times 16\)
\( = 2 + 32 + 64\)
\({\rm{ = 98u}}\)
Thus, the molecular mass of sulphuric acid is \({\rm{98u.}}\)
The molecular weight of sulphuric acid is \(98{\rm{ g/mol}}.\)

Equivalent Weight of Sulphuric Acid

Equivalent weight is defined as the mass of an element/compound/ion which combines or displaces \(1\) part of hydrogen or \(8\) parts of oxygen or \(35.5\) parts of chlorine by mass.
An equivalent weight of any compound, especially acids and bases, depending on the reaction it is being used in.

Equivalent weight \(=\) Molecular weight / Number of replaceable \({{\rm{H}}^{\rm{ + }}}\) ions.
The molecular weight of sulphuric acid is \(98\,{\rm{g}}.\)
Sulphuric acid has two replaceable \({{\rm{H}}^{\rm{ + }}}\) ions.
By applying the values in the above equation
Equivalent weight \( = \;\frac{{98}}{2} = 49{\mkern 1mu} {\rm{g}}{\rm{.}}\)
The equivalent weight of sulphuric acid is \(49{\mkern 1mu} {\rm{g}}{\rm{.}}\)

Manufacture of Sulphuric Acid

Sulphuric acid is one of the most important industrial chemicals worldwide.

Sulphuric acid is manufactured by the Contact Process, which involves three steps:

1. Burning of sulphur or sulphide ores in the air to generate sulphur dioxide.
2. Conversion of sulphur dioxide to \({\rm{S}}{{\rm{O}}_{\rm{3}}}\) by the reaction with oxygen in the presence of a catalyst \(\left( {{{\rm{V}}_2}{{\rm{O}}_5}} \right).\)
3. Absorption of \({\rm{S}}{{\rm{O}}_{\rm{3}}}\) in \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\) to give Oleum.

The \({\rm{S}}{{\rm{O}}_{\rm{2}}}\) produced is purified by removing dust and other impurities such as arsenic compounds.
The key step in the manufacture of \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\) is the catalytic oxidation of \({\rm{S}}{{\rm{O}}_{\rm{2}}}\) with \({{\rm{O}}_{\rm{2}}}\)  to give \({\rm{S}}{{\rm{O}}_{\rm{2}}}\) in the presence of \({{\rm{V}}_{\rm{2}}}{{\rm{O}}_{\rm{5}}}\) (catalyst).
\({\rm{2S}}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{ + }}{{\rm{O}}_{\rm{2}}}\left( {\rm{g}} \right){\rm{\;}} \to {\rm{2S}}{{\rm{O}}_{\rm{3}}}\left( {\rm{g}} \right){\rm{\;}}\)
The reaction is exothermic, reversible and the forward reaction leads to a decrease in volume. Therefore, low temperature and high pressure are favourable conditions for maximum yield. But the temperature should not be too low; otherwise, the rate of reaction will be slow.

The plant is operated at a pressure of \(2\) bar and a temperature of \(720\, {\rm{ K}}.\) The \({\rm{S}}{{\rm{O}}_{\rm{3}}}\) gas from the catalytic converter is absorbed in concentrated \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\) to produce Oleum. Dilution of Oleum with water gives \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}\) of the desired concentration. Thus, two steps are carried out in the industry simultaneously to make the process a continuous one and reduce costs.
\({\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {{\rm{H}}_{\rm{2}}}{{\rm{S}}_{\rm{2}}}{{\rm{O}}_{\rm{7}}}\) (Oleum)
The sulphuric acid obtained by the Contact process is \(96 – 98\% \) pure.

Physical Properties of Sulphuric Acid

1. Pure sulphuric acid is a colourless, dense, oily liquid with a specific gravity of \(1.84\) at \(288{\rm{ K}}.\)
2. It is soluble in water at all concentrations.
3. It forms a constant boiling mixture. The mixture contains \(97.3\% \) of the acid and boils at \(611{\rm{ K}}.\) Hence the aqueous sulphuric acid cannot be concentrated beyond \(97.3\%\) by boiling.
4. It fumes strongly in moist air.
5. It causes severe burns when brought in contact with the skin.

Chemical Properties of Sulphuric Acid

Dissociation:
When pure water-sulphuric acid is boiled, it dissociates into sulphur trioxide and water.

\({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Acidic Character of Sulphuric Acid

It is a typical dibasic acid and turns blue litmus red. It forms two series of salts.
\({\rm{NaOH + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {\rm{NaHS}}{{\rm{O}}_{\rm{4}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)
\({\rm{2NaOH + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Sulphonating Action of Sulphuric Acid

Concentrated sulphuric acid reacts with many organic compounds, for examples., benzene, toluene, etc., and converts them into respective sulphonic acids. For example,
\({{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{6}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}} \to {{\rm{C}}_{\rm{6}}}{{\rm{H}}_{\rm{5}}}{\rm{S}}{{\rm{O}}_{\rm{3}}}{\rm{H + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Precipitation Reactions with Sulphuric Acid

When treated with aqueous solutions of the salts of barium, lead, etc., it forms insoluble sulphates, which get precipitated. For example,
\({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}{\rm{ + BaC}}{{\rm{l}}_{\rm{2}}} \to {\rm{BaS}}{{\rm{O}}_{\rm{4}}} \downarrow {\rm{ + 2HCl}}\)

Reaction with Sulphur Trioxide

It dissolves sulphur trioxide to form Oleum, also referred to as fuming sulphuric acid.

\({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}{\rm{ + S}}{{\rm{O}}_{\rm{3}}} \to {{\rm{H}}_{\rm{2}}}{{\rm{S}}_{\rm{2}}}{{\rm{O}}_{\rm{7}}}\)

Where is Sulphuric Acid Used?

Sulphuric acid is one of the most important chemicals and finds applications in some way or the other in almost all industries. It is used

1. In the manufacture of fertilisers such as ammonium sulphate, superphosphate of lime, etc.
2. In the manufacture of dyestuff, explosives and drugs.
3. In the manufacture of acids like \({\rm{HCl, HN}}{{\rm{O}}_{\rm{3}}}\)
4. In the manufacture of pigments, paints, plastics, etc.
5. In the paper and textile industry.
6. In the manufacture of nitrocellulose products.
7. Metallurgical applications (Example: Cleaning metals before enamelling, electroplating and galvanising).
8. In the leather industry.
9. In storage cells.
10. In the petroleum industry.
11. In the detergent industry.
12. As a dehydrating agent.
13. As a laboratory reagent.

Summary

The most commonly used acid in chemical experiments is Sulphuric acid. It’s an inorganic acid with a lot of strength. H2SO4 is the chemical formula for Sulphuric acid. 2 hydrogen atoms, 1 Sulphur atom, and 4 oxygen atoms make up the molecular formula of Sulphuric acid. Sulphuric acid has many uses in the industry. In addition, it is such an important bulk chemical that the amount of Sulphuric acid a country uses in one year can be seen as a measure of that country’s economic development, that is, how modern or wealthy the country is. The fundamental ideas of Sulphuricacid, Sulphuric acid formula, Sulphuric acid molecular formula, dilute Sulphuric acid formula, structure, chemical characteristics, and applications of acid were explored on this page.

Let’s look at some of the commonly asked questions about Sulphuric Acir:

Q.1. What are the uses of Sulphuric acid?
Ans: Sulphuric acid is used in the manufacture of fertilisers, dyestuff, explosives and drugs It is also used to manufacture acids like \({\rm{HCl, HN}}{{\rm{O}}_{\rm{3}}}.\) It is used widely in metallurgical applications (Example: Cleaning metals before enamelling, electroplating and galvanising). 

Q.2. What is the chemical formula of sulphuric acid?
Ans: The chemical formula of sulphuric acid is \({{\rm{H}}_{\rm{2}}}{\rm{S}}{{\rm{O}}_{\rm{4}}}{\rm{.}}\)

Q.3. While diluting concentrated sulphuric acid, the acid should be added to water and not water to the acid. Explain?
Ans: Dilution of a concentrated acid by adding water is a highly exothermic process. The heat energy is so significant and may instantly turn water into steam, resulting in acid splashing and may cause severe acid burns. So, a concentrated acid should never be diluted by adding water to the acid. But by adding acid gradually to the water, the small amount of heat produced is safely absorbed by the large volume of water. 

Q.4. Is sulphuric acid dangerous to humans?
Ans: The concentrated Sulphuric acid falls accidentally on skin, clothes, or wood, it causes severe burns on the skin, it cuts holes in the clothes and burns the wood producing black spots on its surface.

Q.5. Why is Sulphuric acid called the king of chemicals?
Ans: Sulphuric acid is one of the most important chemicals and is usually referred to as the king of chemicals. It is also known as oil of vitriol as it is used to be prepared from green vitriol in ancient times. It is more reactive than other acids and is highly corrosive. Therefore, it has several applications in different fields, such as being used in a laboratory, in batteries, detergents, in the synthesis of many drugs.