Chemistry 2006 Jamb Examination

The raw material is limestone (CaCO₃). In the blast furnace, limestone acts as a flux. It decomposes when heated to form calcium oxide (CaO), which then reacts with silica (SiO₂) impurities in the ore to form slag (CaSiO₃). This slag floats on molten iron and is removed.

Equations:
CaCO₃ (s) → CaO (s) + CO₂ (g)
CaO (s) + SiO₂ (s) → CaSiO₃ (slag)

Silver nitrate (AgNO₃) decomposes on heating to give metallic silver, brown nitrogen(IV) oxide gas, and oxygen. This is a common test for silver nitrate.

Equation:
2AgNO₃ (s) → 2Ag (s) + 2NO₂ (g) + O₂ (g)

Group IA (alkali metals) such as Na and K are highly reactive due to their low ionization energy and tendency to lose one valence electron to form stable cations. This reactivity prevents them from existing as free elements in nature. Instead, they are found as salts, e.g., NaCl or K₂CO₃.

Example reaction:
2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)

While carbon also exists in free states like graphite and diamond, the question specifies combined state. Carbon occurs combined naturally in wood, carbonates (CaCO₃), and hydrocarbons (e.g., petroleum and natural gas).

Example: CaCO₃ (limestone) contains combined carbon as carbonate ions (CO₃²⁻).

The effectiveness of a solid catalyst depends mainly on its surface area. This is because catalytic reactions occur on the surface of the catalyst. A finely powdered catalyst or one with a porous structure provides more active sites for molecules to collide and react, thus speeding up reactions.

Example: Finely divided Fe is used as a catalyst in the Haber process:
N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g) (Fe catalyst)

Dynamic equilibrium occurs in a reversible reaction when the forward and backward reactions proceed at the same rate. At this point, the concentrations of reactants and products remain constant, but not necessarily equal.

Example:
N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
At equilibrium, rate of forward reaction (formation of NH₃) = rate of backward reaction (decomposition of NH₃).

Zinc ions (Zn²⁺) form a white precipitate of zinc hydroxide, Zn(OH)₂, with NaOH. This precipitate dissolves in excess NaOH to form a colourless solution containing tetrahydroxozincate(II) ions [Zn(OH)₄]²⁻.

Equations:
Zn²⁺ (aq) + 2OH⁻ (aq) → Zn(OH)₂ (s) (white ppt.)
Zn(OH)₂ (s) + 2OH⁻ (aq) → [Zn(OH)₄]²⁻ (aq) (colourless solution)

SO₂ and NO can be oxidized further to form higher oxides.

Equations:
2SO₂ (g) + O₂ (g) → 2SO₃ (g)
2NO (g) + O₂ (g) → 2NO₂ (g)

CO₂ and H₂O are already in their highest oxidation states and do not react further with O₂ under normal conditions.

The flame test for copper salts gives a bluish-green flame. This is due to the excitation of copper ions which emit greenish light when returning to ground state.

Note: Lilac is for K⁺, Yellow for Na⁺, Brick-red for Ca²⁺.

During industrial production of hydrogen by steam reforming of methane, CO₂ is a byproduct. The CO₂ is removed by passing the gas mixture through lime water (Ca(OH)₂ solution), which reacts to form insoluble calcium carbonate.

Equations:
CH₄ (g) + H₂O (g) → CO (g) + 3H₂ (g)
CO (g) + H₂O (g) → CO₂ (g) + H₂ (g)
CO₂ (g) + Ca(OH)₂ (aq) → CaCO₃ (s) + H₂O (l)