Write balanced chemical equations to explain what happens, when:

(i) Mercuric oxide is heated.

(ii) Mixture of cuprous oxide and cuprous sulphide is heated.

(iii) Aluminium is reacted with manganese dioxide.

(iv) Ferric oxide is reduced with aluminium.

(v) Zinc carbonate undergoes calcination.

OR

(i) By the transfer of electrons, illustrate the formation of bond in magnesium chloride and identify the ions present in this compound.

(ii) Ionic compounds are solids. Give reasons.

(iii) With the help of a labelled diagram show the experimental set up of action of steam on a metal.

PART A: Balanced Chemical Equations

(i) Heating of Mercuric oxide:

When red mercuric oxide is heated strongly, it decomposes into liquid mercury and oxygen gas.

$$2\text{HgO(s)} \xrightarrow{\text{Heat}} 2\text{Hg(l)} + \text{O}_2\text{(g)}$$

(ii) Heating a mixture of cuprous oxide and cuprous sulphide:

When a mixture of copper(I) oxide and copper(I) sulphide is heated, they undergo self-reduction to form copper metal and sulphur dioxide gas.

$$2\text{Cu}_2\text{O(s)} + \text{Cu}_2\text{S(s)} \xrightarrow{\text{Heat}} 6\text{Cu(s)} + \text{SO}_2\text{(g)}$$

(iii) Reaction of aluminium with manganese dioxide:

Aluminium reduces manganese dioxide to manganese metal. This is a highly exothermic displacement reaction, and the manganese is obtained in a molten state.

$$3\text{MnO}_2\text{(s)} + 4\text{Al(s)} \xrightarrow{\text{Heat}} 3\text{Mn(l)} + 2\text{Al}_2\text{O}_3\text{(s)} + \text{Heat}$$

(iv) Reduction of ferric oxide with aluminium (Thermite Reaction):

Iron(III) oxide is reduced by aluminium powder. The reaction is highly exothermic, producing molten iron which is used to join cracked railway tracks.

$$\text{Fe}_2\text{O}_3\text{(s)} + 2\text{Al(s)} \xrightarrow{\text{Heat}} 2\text{Fe(l)} + \text{Al}_2\text{O}_3\text{(s)} + \text{Heat}$$

(v) Calcination of zinc carbonate:

Zinc carbonate is heated strongly in the absence or limited supply of air to decompose it into zinc oxide and carbon dioxide gas.

$$\text{ZnCO}_3\text{(s)} \xrightarrow{\text{Heat}} \text{ZnO(s)} + \text{CO}_2\text{(g)}$$

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OR

(i) Formation of Magnesium Chloride ($\text{MgCl}_2$) by Transfer of Electrons:

• Magnesium ($\text{Mg}$): Atomic number = $12$. Electronic configuration = $2, 8, 2$. It has $2$ valence electrons and loses them to achieve a stable octet configuration.

$$\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^{-}$$

• Chlorine ($\text{Cl}$): Atomic number = $17$. Electronic configuration = $2, 8, 7$. It has $7$ valence electrons and needs $1$ electron to complete its octet.

$$\text{Cl} + e^{-} \rightarrow \text{Cl}^{-}$$

Electron Transfer Representation:

$$\text{Mg}^{\bullet}_{\bullet} + 2 \cdot \ddot{\text{Cl}}: \rightarrow [\text{Mg}]^{2+} \left[ :\ddot{\text{Cl}}: \right]^{-}_{2}$$

• Ions present in Magnesium Chloride:

1. Magnesium cation: $\text{Mg}^{2+}$
2. Chloride anion: $\text{Cl}^{-}$

(ii) Why Ionic Compounds are Solids:

Ionic compounds are solids because they consist of oppositely charged ions (cations and anions) held together by very strong electrostatic forces of attraction. These strong forces result in a rigid, closely packed, three-dimensional crystalline lattice structure.

(iii) Experimental Setup of Action of Steam on a Metal:

When steam is passed over a heated metal, it reacts to form the metal oxide and hydrogen gas.

$$\text{Metal} + \text{Steam} \rightarrow \text{Metal Oxide} + \text{Hydrogen}$$

Example:

$$3\text{Fe(s)} + 4\text{H}_2\text{O(g)} \rightarrow \text{Fe}_3\text{O}_4\text{(s)} + 4\text{H}_2\text{(g)}$$

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EXPERIMENTAL SETUP

==================

BOILING TUBE

+----------------------------------+

GLASS WOOL | |=====\ DELIVERY TUBE

SOAKED IN WATER -> | [===] [METAL] | \

+----------------------------------+ \

| | \

v v \

(Heated) (Heated) \ INVERTED

^ ^ \ TEST TUBE

| | \ +-----+

BURNER BURNER \==| H2 | (Gas)

|~~~~~| <- WATER

+----+-----+----+

[ TROUGH ]

+---------------+

``