Sulfuric Acid - Structure, Formula, Properties, Uses, FAQs

Sulphuric acid is usually termed the "king of chemicals" due to its central role in industries that pertain to life. Imagine waking up one morning and finding that batteries no longer work in cars, fertilizers have failed in improving crop yields, and detergents no longer clean. Add this to the importance of sulphuric acid; it is deep within our daily life.

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This Story also Contains

1. Sulphuric Acid: Comprehension
2. Various Uses of Sulphuric Acid
3. Relevance and Applications in Real Life
4. Some Solved Examples
5. Summary

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Sulphuric Acid: Comprehension

Sulphuric acid is a very corrosive, concentrated, oily liquid of colorless to faintly yellow color. It gets dissolved in water, but it releases heat during the process. This, therefore, is an inorganically strong acid made up of sulphur, oxygen, and hydrogen. In addition, this particular acid is one excellent dehydrating and oxidizing agent in most chemical reactions. In the structure, there are two hydrogen atoms and an atom of sulphur combined with four atoms of oxygen. All these atoms combine to form a geometry in the shape of a tetrahedron. Being a strong acid by nature, it completely dissociates in water and releases hydrogen ions that are responsible for its highly conducting and reactive nature.

Various Uses of Sulphuric Acid

The various uses of sulphuric acid lie within a range of industries. Fertilizers like ammonium sulfate and superphosphate, prepared using sulfuric acid, cannot be made without it; therefore, modern chemical farming is out of the window. The application of sulphuric acid can also be seen in the automotive industry, where it forms the bulk of lead-acid batteries to meet the desired chemical conditions in which electrochemical reactions take place to produce electricity. Apart from this, sulfuric acid is used in petroleum refining for the purification of crude oil and also in the production of finer products. It is also used for several chemical works due to its dehydrating action, such as hydrochloric and nitric acids, etc. manufacturing. Besides, sulfuric acid takes part in quite a few pharmaceuticals and dyestuffs preparations and in explosives.

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Preparation

Sulphuric acid is one of the most important industrial chemicals worldwide. Sulphuric acid is manufactured by the Contact Process which involves three steps:
(i) burning of sulphur or sulphide ores in the air to generate SO₂.
(ii) conversion of SO₂ to SO₃ by the reaction with oxygen in the presence of a catalyst (V₂O₅).
(iii) absorption of SO₃ in H₂SO₄ to give Oleum (H₂S₂O₇).

A flow diagram for the manufacture of sulphuric acid is shown in the figure given below. The SO₂ produced is purified by removing dust and other impurities such as arsenic compounds.
The key step in the manufacture of H₂SO₄ is the catalytic oxidation of SO₂ with O₂ to give SO₃ in the presence of V₂O₅ (catalyst).

$2 \mathrm{SO}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \xrightarrow{\mathrm{V}_2 \mathrm{O}_5} 2 \mathrm{SO}_3(\mathrm{~g}) \quad \Delta_{\mathrm{r}} H^{\ominus}=-196.6 \mathrm{kJmol}^{-1}$

The reaction is exothermic, and reversible and the forward reaction leads to a decrease in volume. Therefore, low temperature and high pressure are the favorable conditions for maximum yield. But the temperature should not be very low otherwise rate of reaction will become slow. In practice, the plant is operated at a pressure of 2 bar and a temperature of 720 K. The SO₃ gas from the catalytic converter is absorbed in concentrated H₂SO₄ to produce oleum. Dilution of oleum with water gives H₂SO₄ of the desired concentration. In the industry, two steps are carried out simultaneously to make the process a continuous one and also to reduce the cost.

$\mathrm{SO}_3+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_7$
The sulphuric acid obtained by the Contact process is 96-98% pure.

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Properties

Sulphuric acid is a colourless, dense, oily liquid with a specific gravity of 1.84 at 298 K. The acid freezes at 283 K and boils at 611 K. It dissolves in water with the evolution of a large quantity of heat. Hence, care must be taken while preparing a sulphuric acid solution from concentrated sulphuric acid. The concentrated acid must be added slowly into the water with constant stirring. The chemical reactions of sulphuric acid are a result of the following characteristics: (a) low volatility (b) strong acidic character (c) strong affinity for water and (d) ability to act as an oxidizing agent. In an aqueous solution, sulphuric acid ionizes in two steps.

$\begin{aligned} & \mathrm{H}_2 \mathrm{SO}_4(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{HSO}_4^{-}(\mathrm{aq}) ; K_{\mathrm{a}_1}=\text { very large }\left(K_{\mathrm{a}_1}>10\right) \\ & \mathrm{HSO}_4^{-}(\mathrm{aq})+\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{SO}_4^{2-}(\mathrm{aq}) ; K_{\mathrm{a} 2}=1.2 \times 10^{-2}\end{aligned}$

The larger value of K_a1 (K_a1 >10) means that H₂SO₄ is largely dissociated into H⁺ and HSO^3–. The greater the value of the dissociation constant (K_a), the stronger is the acid. The acid forms two series of salts: normal sulphates (such as sodium sulphate and copper sulphate) and acid sulphates (e.g., sodium hydrogen sulphate). Sulphuric acid, because of its low volatility can be used to manufacture more volatile acids from their corresponding salts.

$2 \mathrm{MX}+\mathrm{H}_2 \mathrm{SO}_4 \rightarrow 2 \mathrm{HX}+\mathrm{M}_2 \mathrm{SO}_4\left(\mathrm{X}=\mathrm{F}, \mathrm{Cl}, \mathrm{NO}_3\right.$

Concentrated sulphuric acid is a strong dehydrating agent. Many wet gases can be dried by passing them through sulphuric acid, provided the gases do not react with the acid. Sulphuric acid removes water from organic compounds; it is evident by its charring action on carbohydrates.

$\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11} \xrightarrow{\mathrm{H}_2 \mathrm{SO}_4} 12 \mathrm{C}+11 \mathrm{H}_2 \mathrm{O}$

Hot concentrated sulphuric acid is a moderately strong oxidizing agent. In this respect, it is intermediate between phosphoric and nitric acids. Both metals and non-metals are oxidized by concentrated sulphuric acid, which is reduced to SO₂.

$\begin{aligned} & \mathrm{Cu}+2 \mathrm{H}_2 \mathrm{SO}_4 \text { (conc.) } \rightarrow \mathrm{CuSO}_4+\mathrm{SO}_2+2 \mathrm{H}_2 \mathrm{O} \\ & \mathrm{S}+2 \mathrm{H}_2 \mathrm{SO}_4 \text { (conc.) } \rightarrow 3 \mathrm{SO}_2+2 \mathrm{H}_2 \mathrm{O} \\ & \mathrm{C}+2 \mathrm{H}_2 \mathrm{SO}_4 \text { (conc.) } \rightarrow \mathrm{CO}_2+2 \mathrm{SO}_2+2 \mathrm{H}_2 \mathrm{O}\end{aligned}$

Uses

• Sulphuric acid is a very important industrial chemical.
• It is needed for the manufacture of hundreds of other compounds and also in many industrial processes.
• The bulk of sulphuric acid produced is used in the manufacture of fertilizers (e.g., ammonium sulphate, superphosphate).
• Other uses are in: (a) petroleum refining (b) the manufacture of pigments, paints, and dyestuff intermediates (c) the detergent industry (d) metallurgical applications (e.g., cleansing metals before enameling, electroplating, and galvanizing (e) storage batteries (f) in the manufacture of nitrocellulose products and (g) as a laboratory reagent.

Relevance and Applications in Real Life

However, the applicability of sulfuric acid does not stop there in industrial scope, rather it extends into everyday life and academic research. Sulfuric acid is even found diluted as an ingredient in some cleaners in most households. These are quite effective against clogs caused by organic materials. Its role in agriculture also cannot be underrated whereby fertilizers containing sulfuric acid derivatives increase crop yields manifold, hence securing food supply for the ever-increasing human population across the globe. In an academic sense, sulfuric acid is also one of the basic reagents found in many laboratories around the world. For students, its use gives real meaning to acid-base reactions and molarity through its involvement in titration. More importantly, its application in the contact process—as a crucial step in the industrial production of sulfuric acid—introduces to most chemistry courses of students with enormous implications in chemical equilibrium and catalysis. Basically, it is the enormous range of applicability for this acid that underlines and places it at the very core of practical and theoretical situations, often broaching detailed studies and research on it.

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Some Solved Examples

Example 1
Question:
Match List - I with List - II

List-1 Industrial process List - II Application
(a) Haber's process (i) HNO₃ synthesis
(b) Ostwald's process (ii) Aluminium extraction
(c) Contact process (iii) NH₃ synthesis
(d) Hall - Heroult process (iv) H₂SO₄ synthesis

Choose the correct answer from the options given below:
1. (a) - (iii), (b) - (i), (c) - (iv), (d) - (ii)
2. (a) - (ii), (b) - (iii), (c) - (iv), (d) - (i)
3. (a) - (iii), (b) - (iv), (c) - (i), (d) - (ii)
4. (a) - (iv), (b) - (i), (c) - (ii), (d) - (iii)

Solution:
1. Haber's process is used for NH₃ synthesis:

[N₂+3H₂⇌FeMo2NH₃[N2+3H2⇌FeMo2NH3]
2. Ostwald's process is used for HNO₃ synthesis using a Pt catalyst.
3. Contact process is used for H₂SO₄ synthesis using V₂O₅ catalyst.
4. In the Hall-Heroult process, electrolytic reduction of impure alumina can be done (Aluminium extraction).

Hence, the correct answer is option 1: (a) - (iii), (b) - (i), (c) - (iv), (d) - (ii).

Example 2
Question:
Match List - I with List - II

List - I List - II
(a) Deacon's process (i) ZSM -5
(b) Contact process (ii) CuCl₂
(c) Cracking of hydrocarbons (iii) Particles 'Ni'
(d) Hydrogenation of vegetable oils (iv) V₂O₅

Choose the most appropriate answer from the options given below:
1. (a) - (ii), (b) - (iv), (c) - (i), (d) - (iii)
2. (a) - (i), (b) - (iii), (c) - (ii), (d) - (iv)
3. (a) - (iv), (b) - (ii), (c) - (i), (d) - (iii)
4. (a) - (iii), (b) - (i), (c) - (iv), (d) - (ii)

Solution:
1. CuCl₂ is used as a catalyst in Deacon's process.
2. In the manufacture of H₂SO₄ (Contact process), V₂O₅ is used as a catalyst.
3. ZSM-5 is used as a catalyst in the cracking of hydrocarbons.
4. Ni catalysts enable the hydrogenation of vegetable oils (fats).

Correct matching: (a) - (ii), (b) - (iv), (c) - (i), (d) - (iii).

Hence, the correct answer is option 1: (a) - (ii), (b) - (iv), (c) - (i), (d) - (iii).

Example 3
Question:
Low volatile nature of (H₂SO₄) is due to:
1. Hydrogen bonding
2. Van der Waal's forces
3. Strong bonds
4. None

Solution:
The low volatile nature of ((H₂SO₄) is due to hydrogen bonding.

Therefore, the correct answer is option 1: Hydrogen bonding.

Summary

This chemical substance is applied vastly in different industries and in academia, simply because of its versatile nature. Major end-uses of sulphuric acid are in the manufacture of fertilizers and petroleum refining, and in batteries. Its application in goods like drain cleaners and that it helps increase agricultural productivity make its existence quite important in everyday life. Academically, that has been one of the cornerstones of chemical education and research and is usually taught to convey some of the basic principles related to the study of chemistry. The properties, application, and relevance of the sulphuric acid may be helpful in placing in perspective how important this compound is in modern society.

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