Sulphuric Acid – Structure, Properties and Molecular Weight
Acids are those substances that release hydrogen or hydronium ions when dissolved in their solutions. Acids can also be defined as those substances which donate a proton. Sulphuric Acid is a strong mineral acid, which is represented by the chemical formula H2SO4. Sulphuric Acid is also known as the king of chemicals due to its immense uses in various industries, especially heavy industries. It is also called matting acid and the oil of vitriol. In the eighteenth century, Sulphuric Acid was produced from green vitriol. The Sulphuric Acid thus developed has an oily look. So, it was then named the oil of vitriol.
Sulfuric acid is a mineral acid whose molecular formula contains one sulphur atom, four oxygen atoms with two hydrogen atoms attached directly to two of the oxygen atoms forming the -OH group, hence forming the chemical formula of sulfuric acid is H2SO4.
It is a colourless, odourless and highly corrosive substance having great commercial importance and is used in most industries. Sulfuric acid is an oily liquid that is inherently vicious as it is highly soluble in water and is an acid rain component as well.
It is also used as a rust preventive compound for steel and also in large quantities by metal manufacturers. However, sulfuric acid is a dangerous and toxic chemical that can cause inflammation and burns in the airways, nose and throat if inhaled.
H2SO4 Chemical Name
The chemical name of H2SO4 is hydrogen sulphate or di-hydrogen sulphate. It contains two atoms of hydrogen, one atom of sulphur, and four atoms of oxygen. It has an atomicity of seven.
Hydrogen sulphate is basically an ionic bond. The two ions participating in this bond are hydrogen ion (cation) and sulphate ion (anion).
H2SO4 Structure
The Sulphuric Acid structure can be described as follows: -
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Properties of Sulphuric Acid
Strong Acid: Completely dissociates into ions in its aqueous solution
Oxidising Agent: It tends to oxidise other substances in a reaction by donating its oxygen atoms. In the following reactions, it oxidises carbon and sulphur.
2H2SO4 + C —-> 2H2O + 2SO2 + CO2
2H2SO4 + S —-> 2H2O + 3SO2
Basicity: The basicity of an acid is the number of hydrogen ions it releases per molecule. Sulphuric Acid is a dibasic acid and releases two hydrogen ions per molecule.
Dehydrating Agent: Sulphuric Acid has hygroscopic properties, which means that it can attract and retain moisture from its environment. This property makes it a good dehydrating agent as it can take up and retain moisture from the surroundings and keep them dry.
It has a high boiling point of 337 °C and a melting point of 10 °C.
It turns blue litmus red and has a pH of around one or less.
It is highly corrosive, making it dangerous to touch.
In sulfuric acid, there is 1 sulphur atom, 4 oxygen atoms, and two hydrogen atoms that bond directly to two oxygen atoms to form two OH groups. Molecules are covalently bonded and have a tetrahedral structure.
Molecular Weight of Sulphuric Acid
The molecular mass is the mass of a substance, which is calculated by adding up the atomic mass of every atom present in one molecule of that substance.
Sulphuric Acid contains three types of atoms, and we need to know the atomic mass of each of those. They are written below.
Atomic Mass of Hydrogen = 1 u
Atomic Mass of Sulphur = 32 u
Atomic Mass of Oxygen = 16 u
(Note: The above masses are a good approximation. We have excluded decimals for easier calculation)
We know that one molecule of hydrogen sulphate contains two atoms of hydrogen, one atom of sulphur, and four atoms of oxygen, the masses of which are given below.
Mass of 2 Hydrogen Atoms = 1 x 2 = 2 u
Mass of 1 Sulphur Atom = 32 u
Mass of 4 Oxygen Atoms = 16 x 4 = 64 u
The molecular mass of hydrogen sulphate is equal to the sum of all its atoms.
Molecular Mass of Hydrogen Sulphate = 2 + 32 + 64
= 98 u
Therefore, the molecular mass of Sulphuric Acid is 98 u.
H2SO4 Molar Mass
Molar mass is the mass of one mole of a substance, measured in grams. One mole of a substance is defined as the Avogadro number (6.023 x 1023) molecules of that substance.
Using the atomic mass of an individual atom and multiplying that by the conversion factor grams per mole (g/mol), you can determine the molar mass of that element.
The molar mass constant (our conversion factor) is defined as 0.001 kg/mol or 1 g/mole. Therefore, the Sulphuric Acid molar mass is 98 g/mole.
The molecular formula of sulfuric acid, H2SO4 shows that one molecule of sulfuric acid (H2SO4) contains 2 moles of hydrogen atoms, 1 mole of sulfur, and 4 moles of oxygen atoms. Therefore, the molecular mass of H2SO4 is equal to the sum of the masses of 2 mol of the hydrogen atom, 1 mol of the sulfur atom, and 4 mol of the oxygen atom. The atomic weight of hydrogen is 1u, the atomic weight of sulfur is 32u, the atomic weight of oxygen is 16u, and the molecular weight of sulfuric acid can be calculated as follows.
Molecular weight of H2SO4 = mass of 2 mol hydrogen atom + mass of 1 mol sulfur + mass of 4 mol oxygen atom
= (2 × 1) + 32 +( 4 × 16 )
= 2 + 32 + 64
= 98u
Therefore, the molecular weight of sulfuric acid is 98u and the molecular weight of sulfuric acid is 98 g / mol.
Sulphuric Acid Uses
1. It is used to make fertilisers.
2. It is used in the manufacture of steel and iron. It is also used as a cleaning agent in the industrial sector to erase rust from steel and iron.
3. It is used in the chemical manufacturing industry. It is used to make phosphoric acid, hydrochloric acid, nitric acid, sulphate salts, synthetic detergents, dyes and pigments, explosives, medicines, and ammonium sulphate.
4. It is used for oil processing.
5.It functions as a catalyst in the reaction to convert cyclohexanone oxime to caprolactam. This reaction is used in the production of nylon.
6. It is used to make batteries. In lead-acid batteries, Sulphuric Acid functions as an electrolyte. It can be used in storage batteries. Since it is present in a car battery, it is also known as car battery acid.
7. In the industry:
Up to 50% of this produced liquid is used in the production of phosphoric acid, which is used in the production of phosphoric acid fertilizers. It is also used in the manufacture of Pigment, paints, plastics etc, manufacture of metals such as copper and zinc, 5% of the acid produced is used in the production of fibres, the manufacture of explosives and drugs, in leather and petroleum industry etc. It is used in most industries.
8. At Home:
It is a very dangerous chemical and should be handled with a lot of care. It is used in acid drain cleaners. Due to its high drainage, it can be used to remove the tissue paper.
9. Catalyst:
It is used as a catalyst in the nylon manufacturing process. Used in the Mannheim process in the manufacture of HCl.
10. Drugs and Ointment
It is used to damage the DNA of cancer cells in the manufacture of chemotherapeutic agents. It is also used in ointments to treat various skin infections.
Physical Properties of Sulphuric Acid
Pure sulfuric acid is a colourless, odourless, high density, oily liquid with a specific gravity of 1.84 at 288 K.
It is highly soluble in water at all concentrations.
It contains 97.3% of acid and boils at 611 K. Therefore, aqueous sulfuric acid cannot be concentrated above 97.3% by boiling.
It will fume in the humid air.
If sulphuric acid touches the skin, it can cause severe burns.
Solved Examples
Question 1. Show the Reaction Between Sulphuric Acid and potassium.
Answer:
Acids react with active metals to form metal salts and hydrogen gas. Potassium reacts with Sulphuric Acid to form potassium sulphate and hydrogen gas.
H2SO4 + 2K————> K2SO4 + H2
FAQs on Sulphuric Acid
1. What is sulphuric acid and what is its chemical formula?
Sulphuric acid is a highly corrosive, strong mineral acid. It is an oily, colourless, and odourless liquid that is highly soluble in water. Due to its immense importance in various industries, it is often called the 'King of Chemicals'. The chemical formula for sulphuric acid is H₂SO₄.
2. How is the molecular mass of sulphuric acid (H₂SO₄) calculated?
The molecular mass is the sum of the atomic masses of all atoms in a molecule. For H₂SO₄, the calculation is as follows:
- Atomic mass of Hydrogen (H) = 1 u
- Atomic mass of Sulphur (S) = 32 u
- Atomic mass of Oxygen (O) = 16 u
Molecular Mass of H₂SO₄ = (2 × Atomic Mass of H) + (1 × Atomic Mass of S) + (4 × Atomic Mass of O)
= (2 × 1) + 32 + (4 × 16)
= 2 + 32 + 64
= 98 u.
Therefore, the molar mass is 98 g/mol.
3. What is the structure of a sulphuric acid molecule?
The sulphuric acid molecule has a tetrahedral geometry with a sulphur atom at the centre. The central sulphur atom is covalently bonded to four oxygen atoms. Two of these oxygen atoms are linked via double bonds (S=O), and the other two are linked via single bonds (S-OH). These two -OH groups are responsible for its acidic properties.
4. Why is sulphuric acid classified as a strong and dibasic acid?
Sulphuric acid is classified as:
- Strong Acid: Because it completely ionises or dissociates in an aqueous solution, releasing a high concentration of hydrogen ions (H⁺).
- Dibasic Acid: The term 'dibasic' means it can donate two protons (hydrogen ions) per molecule. It does this in two steps, first releasing one H⁺ ion to form the bisulphate ion (HSO₄⁻), and then the second H⁺ ion from the bisulphate ion.
5. What are the most common uses of sulphuric acid in industry and at home?
Sulphuric acid is a vital chemical with widespread applications. Key uses include:
- Fertiliser Production: Used to manufacture phosphoric acid, which is then used to make phosphate fertilisers like ammonium sulphate.
- Chemical Manufacturing: A key reagent in producing other acids (like hydrochloric acid), detergents, dyes, and pigments.
- Metal Processing: Used for 'pickling' of steel, which involves removing rust and scale from iron and steel surfaces before they are sold.
- Batteries: Acts as the electrolyte in lead-acid storage batteries, commonly found in cars.
- Petroleum Refining: Used to remove impurities from gasoline and other refinery products.
6. How does concentrated sulphuric acid work as a powerful dehydrating agent?
Concentrated sulphuric acid has a very strong affinity for water. This hygroscopic property allows it to remove water molecules from other compounds. For example, when added to sugar (C₁₂H₂₂O₁₁), it removes the hydrogen and oxygen atoms in a 2:1 ratio (as water), leaving behind a black, spongy mass of carbon. This demonstrates its powerful dehydrating action.
7. What is the Contact Process for manufacturing sulphuric acid, as per the CBSE syllabus?
The Contact Process is the modern industrial method for producing sulphuric acid and involves three main steps:
- Production of Sulphur Dioxide: Sulphur is burned in air to produce sulphur dioxide gas (S + O₂ → SO₂).
- Catalytic Oxidation: The sulphur dioxide is then oxidised to sulphur trioxide using a vanadium pentoxide (V₂O₅) catalyst at a temperature of about 450°C and a pressure of 1-2 atm (2SO₂ + O₂ ⇌ 2SO₃).
- Absorption of Sulphur Trioxide: The sulphur trioxide is absorbed into concentrated H₂SO₄ to form oleum (H₂S₂O₇), which is then diluted with water to produce sulphuric acid of the desired concentration.
8. What is the crucial safety rule to follow when diluting concentrated sulphuric acid?
The most important safety rule is to always add the acid slowly to the water, never the other way around. The dilution of sulphuric acid is a highly exothermic process, meaning it releases a large amount of heat. Adding water to acid causes an immediate, violent boiling and splashing of the concentrated acid, which can cause severe burns. Adding acid to water allows the larger volume of water to absorb and dissipate the heat more safely.
9. What is the difference in chemical behaviour between concentrated and dilute sulphuric acid?
The primary difference lies in their chemical properties based on water content:
- Concentrated H₂SO₄: Contains very little water. It acts as a strong oxidising agent and a dehydrating agent. For example, it can oxidise non-metals like carbon and sulphur.
- Dilute H₂SO₄: Contains a large amount of water. It primarily behaves as a typical strong acid, exhibiting properties like reacting with metals to produce hydrogen gas and neutralising bases to form salt and water. It does not act as an effective oxidising or dehydrating agent.
10. How can a sulphuric acid spill be safely neutralised?
A sulphuric acid spill should be neutralised carefully using a weak base. A common and safe substance to use is baking soda (sodium bicarbonate, NaHCO₃) or soda ash (sodium carbonate, Na₂CO₃). The weak base should be sprinkled liberally over the spill area to neutralise the acid, converting it into a harmless salt and water, before cleaning it up.
