Question

Name the following:

(a) Gases obtained by treating carbon with hot concentrated sulphuric acid.

(b) Substance which turns from blue to white, when concentrated sulphuric acid is added to it.

(c) Gas obtained when dilute sulphuric acid is treated with sodium bisulphite.

(d) Solution obtained by dissolving sulphur trioxide in 98% sulphuric acid.

(e) Products obtained by treating ferrous sulphide with dilute sulphuric acid.

(f) The precipitate obtained by treating aqueous lead nitrate with dilute sulphuric acid.

Answer 1

(a)

Part 1: Carbon and Sulphuric Acid

1. Carbon ($\mathrm{C}$) is a non-metal.
2. Concentrated sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) is a strong acid.

Part 2: Chemical Reaction between carbon and sulphuric acid

1. Carbon reacts with hot concentrated sulphuric acid to produce water (${\mathrm{H}}_2\mathrm{O}$), sulphur dioxide gas (${\mathrm{SO}}_2$) and carbon dioxide gas (${\mathrm{CO}}_2$).
2. The reaction takes place according to the following balanced chemical equation:
   $\mathrm{C}\left(\mathrm{s}\right)+2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$
3. In this reaction, concentrated sulphuric acid acts as an oxidizing agent that oxidises carbon to carbon dioxide gas.

Hence, the names of the gases obtained in this reaction are sulphur dioxide gas and carbon dioxide gas.

(b)

Part 1:Dehydrating Reactions:

1. Dehydrating reactions are typical chemical reactions in which water is removed from the reactant molecules in the presence of a dehydrating agent such as concentrated sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$).
2. Concentrated sulphuric acid has a strong affinity towards water (${\mathrm{H}}_2\mathrm{O}$) molecules.

Part 2: Chemical Reaction between Copper(II) sulphate pentahydrate and sulphuric acid

1. The dehydration reaction of blue colored copper(II) sulphate pentahydrate (${\mathrm{CuSO}}_4·5{\mathrm{H}}_2\mathrm{O}$) with concentrated sulphuric acid gives white colored anhydrous copper(II) sulphate (${\mathrm{CuSO}}_4$) and five water molecules $\left({\mathrm{H}}_2\mathrm{O}\right)$.
2. The above reaction takes place according to the following balanced chemical equation:
   $\underset{\left(\mathrm{blue}\right)}{{\mathrm{CuSO}}_4·5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)}\stackrel{\mathrm{Conc}.{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }\underset{\left(\mathrm{white}\right)}{{\mathrm{CuSO}}_4\left(\mathrm{s}\right)}+5{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)$
3. In the above reaction, concentrated sulphuric acid acts as a strong dehydrating agent that removes water from copper(II) sulphate pentahydrate.

The name of the substance that changes from blue to white in this reaction is copper(II) sulphate pentahydrate.

(c)

Part 1: Sodium bisulphite and Sulphuric Acid

1. Sodium bisulphite (${\mathrm{NaHSO}}_3$) is an inorganic sodium salt and the counterpart is sulphite anion.
2. Concentrated sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) is a strong acid.

Part 2: Chemical Reaction between Sodium bisulphite and sulphuric acid

1. Sodium bisulphite can react with dilute sulphuric acid to form water (${\mathrm{H}}_2\mathrm{O}$), sulphur dioxide gas (${\mathrm{SO}}_2$) and sodium sulphate (${\mathrm{Na}}_2{\mathrm{SO}}_4$).
2. The reaction takes place according to the following balanced chemical equation:
   $2{\mathrm{NaHSO}}_3\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)$
3. In the above reaction, only sulphur dioxide gas is released when dilute sulphuric acid is treated with sodium bisulphite.

Therefore, the name of the gas obtained in this reaction is sulphur dioxide gas.

(d)

Part 1: Absorption of sulfur trioxide by 98% sulphuric acid.

1. Sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) is a strong acid that absorbs sulphur trioxide (${\mathrm{SO}}_3$) to produce the oleum solution.
2. Since water does not absorb sulphur trioxide directly.

Part 2: Reaction between 98% sulphuric acid and sulphur trioxide.

1. ${\mathrm{SO}}_3\left(\mathrm{g}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to \underset{(\mathrm{pyrosulphuric}\mathrm{acid})}{{\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7\left(\mathrm{aq}\right)}$
2. In the above reaction, sulphur trioxide is dissolved in concentrated sulphuric acid to form the pyrosulfuric acid (oleum) solution.

Hence, the name of the solution produced by dissolving sulphur trioxide in 98% sulphuric acid is pyrosulphuric acid (oleum).

(e)

Treatment of ferrous sulphide with dilute sulphuric acid:

1. Ferrous sulphide ($\mathrm{FeS}$) reacts with dilute sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) to produce ferrous sulphate (${\mathrm{FeSO}}_4$) salt and hydrogen sulphide gas (${\mathrm{H}}_2\mathrm{S}$).
2. The above reaction takes place according to the below chemical equation.
   $\mathrm{FeS}\left(\mathrm{s}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{FeSO}}_4\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)$
3. Therefore, the names of the products formed in this reaction are ferrous sulphate and hydrogen sulphide.

(f)

Part 1: Definition of precipitate reaction

A precipitation reaction is a chemical reaction in which an insoluble salt is produced when aqueous solutions of two soluble salts are mixed.

Part 2: Reaction of lead nitrate with dilute sulphuric acid.

1. Lead nitrate reacts with dilute sulphuric acid to form the products of lead sulphate (${\mathrm{PbSO}}_4$) (a white precipitate) and nitric acid (${\mathrm{HNO}}_3$).
2. The reaction takes place according to the following balanced chemical equation:
   $\mathrm{Pb}{\left({\mathrm{NO}}_3\right)}_3\left(\mathrm{aq}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{PbSO}}_4\left(\mathrm{s}\right)+{\mathrm{HNO}}_3\left(\mathrm{aq}\right)$
3. The final products are lead sulphate and nitric acid.

Hence, the name of the precipitate obtained in this reaction is lead sulphate.