The p-Block Elements

Sulphuric Acid

You surely must have come across a lot of experiments with sulphuric acid. Haven’t you? But, have you ever put it directly in water? NO! Never ever do that! Why? Let’s find out. In this chapter, we will read all about sulphuric acid and its properties. In the end, we will also look at its uses. Let us first start with what it is.

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What is Sulphuric Acid?

Sulphuric acid or as we write it, H2SO4, is an odourless and colourless, oily liquid that is very corrosive. People named it Oil of Vitriol. On account of its wide applications, it has alluded as the ‘King of Chemicals’. We can find it in both combined and free state.

sulphuric acid

Manufacturing Process

How do you think we can manufacture sulphuric acid? Well, we can commercially produce this by two techniques. They are:

  • Lead chamber process
  • Contact process

Let us now look at these processes closely.

1) Contact Process

The contact process has three major steps:

  • Step – I: Production of Sulphur Dioxide

We can make this by heating sulphur or sulphide ores, for example, iron pyrites in excess of air.

S (Sulphur)   +   O2(Oxygen)   +   Δ(Heating)    →    SO2(Sulphur dioxide)

4FeS(Iron pyrites)   +   7O2(Oxygen)   +   Δ(heating)    →    2Fe2O3(Ferric Oxide)  +  4SO2(Sulphur dioxide)

  • Step -II: Formation of Sulphur Trioxide

We can oxidize Sulphur dioxide to Sulphur trioxide with atmospheric oxygen by using V2O5 as a catalyst.

2SO2(Sulphur dioxide)   +   O2(Oxygen)   +   V2O5(Catalyst)   →    SO3(Sulphur trioxide)

  • Step -III: Conversion of Sulphur Trioxide into Sulphuric Acid

We break down the sulphur trioxide from the above step in 98% sulphuric acid to give pyrosulphuric acid or oleum. We, then, dilute the Oleum with water to give sulphuric acid of the desired concentration.

SO3(Sulphur trioxide)   +  H2SO4(Sulphuric acid-98%)    →    H2S2O7(Pyrosulphuric acid/Oleum)

H2S2O7(Pyrosulphuric acid/Oleum)    +  H2O(Dilution)    →     2H2SO4(Sulphuric acid)

2) Lead Chamber Process

Lead Chamber process is one of the most common manufacturing strategies that results in around 50-60 B grade acids. In this process, we use the wet SO2 (Sulphur Dioxide) in the presence of nitrogenous oxides (dynamic impetus). It gets oxidised and forms sulphur trioxide with the oxygen exhibit in the air. We then react Sulphur trioxide with water to get H2SO4. The reactions are:

2SO2   +   O2    →   2SO3

SO3   +   H2O   →    H2SO4

Physical Properties 

  • Sulphuric acid is a thick, colourless and an oily fluid.
  • It has a specific gravity of 1.84 at 298 K.
  • The boiling point of the acid is 611 K. It attributes its higher boiling point and thickness to hydrogen bonding.
  • The strong acid reacts with water vigorously releasing quite a lot of heat. Therefore, you must never add water to sulphuric acid. Instead, you should add the acid to water, slowly with proper stirring.

Chemical Properties 

  • Sulphuric acid is a strong dibasic acid. It is diprotic and ionises in two stages in the aqueous solution.
  • It is highly corrosive and reactive and is soluble in water. Sulphuric acid has a very high oxidising power and thus, acts as a strong oxidising agent. It has very low volatility.
  • We use this acid as a part of the preparation of more volatile acids from their comparing salts because of its low volatility.
  • Concentrated sulphuric acid is a very strong dehydrating agent. This property is utilized as a part of drying many wet gases which do not react with the acid.
  • It additionally expels water from natural mixes like starches.
  • As it is a good oxidising agent, it can oxidise both non-metals as well as metals. It itself reduces to sulphur dioxide.

Some Common Reactions

  • Hot concentrated sulphuric acid oxidizes copper to copper sulphate.

Cu   +    2H2SO4  →    CuSO +   SO2   +   H2O

  • Concentrated sulphuric acid gives out hydrogen chloride from sodium chloride and hydrogen fluoride from calcium fluoride.

CaF2    +   H2SO4  →     CaSO  +  2HF

  • It burns glucose, sugar, and starch to carbon.

C12H22O11   +   (H2SO4)    →  12C   +  11H2O

Solved Example for You

Q: Write down the main uses of sulphuric acid.

Ans: The uses of sulphuric acid are:

  • It is a common ingredient in the preparation of fertilisers like ammonium sulphate and superphosphate
  • We use it in the manufacture of dyes, shades, and paints.
  • It is a common ingredient in the manufacture of explosives, for example, TNT.
  • Other imperative chemicals like hydrochloric acid, phosphoric acid, nitric acid, and sodium carbonate need the presence of sulphuric acid. Without sulphuric acid, we cannot obtain the chemicals.
  • We utilise it as a part of the refining of petroleum.
  • It acts as a pickling agent.
  • It is common as a laboratory agent, an oxidizing and dehydrating agent.
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