Question

Describe laboratory method of preparation of sulphur dioxide giving chemical equations. Give chemical equations of the reactions of sulphur dioxide with potassium permanganate and lime water.

Answer 1

We know that sulphur dioxide is a common gas that has a pungent smell. Some of the uses of sulfur dioxide are,
-We use it in refining lamp oil and other petroleum items.
-It is used as a common disinfectant and a fumigant.
-It is used as a glue solvent.
-We use it as a refrigerant in refrigerators.
-It is used as an additive for wines, meat, dry natural products etc.

Complete step by step answer:

In laboratory:
We can prepare sulphur dioxide by the action of dilute sulphuric acid on sulphites. Reaction of sodium sulfite and sulfuric acid gives sodium sulfate, water and sulfur dioxide.
We can write the chemical reaction as,
$N{a_2}S{O_3} + {H_2}S{O_4}\xrightarrow{{}}N{a_2}S{O_4} + {H_2}O + \,\,S{O_2} \uparrow \\\ Sodium\,\,\,\,\,\,Sulfuric\,\,\,\,\,\,\,\,\,\,\,Sodium\,\,\,\,\,Water\,\,Sulfur \\\ sulfite\,\,\,\,\,\,\,\,\,acid\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dioxide \\\$
We can prepare sulfur dioxide, by gently heating copper in a flask with concentrated sulfuric acid.
We can write the chemical reaction as,
$Cu\,\,\,\,\,\,\,\,\,\,\, + \,\,\,\,\,\,\,\,\,\,\,2{H_2}S{O_4}\xrightarrow{{}}CuS{O_4} + {H_2}O + \,\,S{O_2} \uparrow \\\ Copper\,\,\,\,\,\,\,\,\,\,\,\,Sulfuric\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Copper\,\,\,\,Water\,\,Sulfur \\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,acid\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dioxide \\\$
We can prepare sulfur dioxide by blazing sulfur in the air. We can write the chemical reaction as,
$S\,\,\,\,\,\,\,\,\,\,\, + {O_2}\xrightarrow{\Delta }S{O_2} \\\ Sulfur\,\,\,Oxygen\,\,\,\,\,\,Sulfur \\\ \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dioxide \\\$
When sulfur dioxide is reacted with potassium permanganate, decolourization of pink permanganate solution happens. We can write the chemical equation as,
$5S{O_2}\,\,\,\,\,\,\, + \,\,\,\,\,2KMn{O_4}\,\,\,\,\,\,\,\,\,\,\,\, + 2{H_2}O\xrightarrow{{}}{K_2}S{O_4}\,\,\,\,\,\,\,\,\,\,\, + 2MnS{O_4}\,\,\,\, + \,\,\,\,\,\,2{H_2}S{O_4} \\\ Sulfur\,\,\,\,\,\,\,\,\,\,\,\,\,Potassium\,\,\,\,\,\,\,\,\,\,\,Water\,\,\,\,\,\,\,\,\,\,\,\,Potassium\,\,\,\,\,\,Manganese\,\,\,\,\,\,\,\,Sulfuric \\\ dioxide\,\,\,\,\,\,\,\,\,\,permanganate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,acid \\\$
When sulfur dioxide is reacted with lime water (calcium hydroxide), calcium sulfite and water is formed. We can write the chemical equation as,
$S{O_2}\,\,\,\,\,\,\, + \,\,\,\,\,Ca{\left( {OH} \right)_2}\,\,\,\,\,\xrightarrow{{}}\,\,CaS{O_3} \downarrow \,\, + \,{H_2}O \\\ Sulfur\,\,\,\,\,\,\,\,\,\,Calcium\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Calcium\,\,\,\,Water \\\ dioxide\,\,\,\,\,\,\,\,\,hydroxide\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfite\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, \\\$

Note:
The reaction of dilute sulfuric acid and sodium sulfite is an example of double replacement reaction.
Sulfuric acid in reaction with sodium sulfite gives sodium sulfate and sulfurous acid. We can write the equation as,
${H_2}S{O_4} + N{a_2}S{O_3}\xrightarrow{{}}N{a_2}S{O_4} + {H_2}S{O_3} \\\ Sulfuric\,\,\,Sodium\,\,\,\,\,\,\,\,\,\,\,\,\,\,Sodium\,\,\,\,\,\,Sulfurous \\\ acid\,\,\,\,\,\,\,\,\,\,\,sulfite\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,acid \\\$
We know the sulfurous acid is unstable, there it decomposes to form sulfur dioxide and water.
${H_2}S{O_3}\xrightarrow{{}}{H_2}O + S{O_2} \\\ Sulfurous\,\,\,\,\,\,\,Water\,\,Sulfur \\\ acid\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dioxide \\\$
We can write the overall reaction as,
$N{a_2}S{O_3} + {H_2}S{O_4}\xrightarrow{{}}N{a_2}S{O_4} + {H_2}O + \,\,S{O_2} \uparrow \\\ Sodium\,\,\,\,\,\,Sulfuric\,\,\,\,\,\,\,\,\,\,\,Sodium\,\,\,\,\,\,Water\,\,Sulfur \\\ sulfite\,\,\,\,\,\,\,\,\,acid\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,sulfate\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,dioxide \\\$
Some of the properties of sulfur dioxide are,
It has a pungent smell.
It is an acidic oxide that is water-soluble.
Sulfur dioxide on reaction with oxygen gives sulfur trioxide. We can write reaction as,
$S{O_2}\,\,\,\,\,\,\,\, + \,\,\,\,\,\,{O_2}\,\xrightarrow{\Delta }\,\,\,\,\,\,\,S{O_3} \\\ Sulfur\,\,\,\,\,Oxygen\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Sulfur \\\ dioxide\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,trioxide \\\$
Sulfur dioxide on reaction with sodium hydroxide gives sodium sulfite and water. We can write the reaction as,
$S{O_2} + \,\,\,\,\,2NaOH\xrightarrow{{}}N{a_2}S{O_3} + {H_2}O \\\ Sulfur\,\,\,\,Sodium\,\,\,\,\,\,\,\,\,\,\,\,\,\,Sodium\,\,\,\,\,Water \\\ dioxide\,\,\,hydroxide\,\,\,\,\,\,\,\,sulfite \\\$
We can use sulfur dioxide as a reagent and as a solvent in the laboratory. It also plays a role of refrigerant in cold storage plants.