The S-block Elements

Limestone:

• A raw material for cement.
• It is used as a building material in the form ofmarble and in the manufacture of quick lime.
• used in the manufactureof high quality paper. It is also used as anantacid, mildabrasive in tooth paste, aconstituent of chewing gum, and a filler incosmetics.

Cement:

• It is used in concrete and reinforcedconcrete, in plastering and in the construction
• of bridges, dams and buildings

Plaster of Paris:

• It is used in the building industry as well as plasters.
• It is usedfor immobilising the affected part of organ wherethere is a bone fracture or sprain.
• It is alsoemployed in dentistry, in ornamental work andfor making casts of statues and busts.

(i) Caustic soda
It is used in (a) the manufacture of soap, paper, artificial silk and a number of chemicals, (b) in petroleum refining, (c) in the purification of bauxite, (d) in the textile industries for mercerising cotton fabrics, (e) for the preparation of pure fats and oils, and (f) as a laboratory reagent.

(ii) Sodium carbonate
(a) It is used in water softening, launderingand cleaning.

(b) It is used in the manufacture of glass, soap, borax and caustic soda.

(c) It is used in paper, paints and textileindustries.

(d) It is an important laboratory reagent bothin qualitative and quantitative analysis

(iii) Quick lime

(a) It is an important primary material formanufacturing cement and is the cheapest

form of alkali.

(b) It is used in the manufacture of sodiumcarbonate from caustic soda.

(c) It is employed in the purification of sugarand in the manufacture of dye stuffs.

(i) Sodium metal is manufactured by electrolysis of a fused mass of NaCl 40% and CaCl₂ 60% in Down's cell at 873 K, using iron as cathode and graphite as anode. Na is liberated at the cathode.
At cathode:
Na⁺ + e^– → Na (l)
At anode:
2Cl^–  (melt) → Cl₂  (g) + 2e^–.
(ii) Sodium hydroxide is manufactured by electrolysis of an aqueous solution of NaCl (brine) in Castner-Kellner cell.
At cathode:
Na⁺ + e^– → Na
2Na + Hg → Na – Hg + 2H₂O
2Na- Hg + 2H₂O → 2NaOH +H₂ +Hg
At anode:
Cl^– – e^– → Cl
Cl + Cl→ Cl₂
(iii) Sodium peroxide:

Sodium is heated in excess of oxygen to form sodium peroxide. Initially, sodium oxide is obtained which reacts with more oxygen to form sodium peroxide.

4Na+O₂→2Na₂O

2Na₂O+O2→Na₂O₂
(iv)Sodium carbonate is obtained by Solvay ammonia process.
NaCl + NH₃ + H₂O + CO₂ → NaHCO₃→ + NH₄Cl

2NaHCO₃→ Na₂CO₃ + H₂O + CO₂

(a) Nitrates of both group 1 and group 2 elements are soluble in water because hydration energy is more than the lattice energy.
Nitrates of both group 1 and group 2 elements are thermally unstable but they decompose differently except LiCO₃ e.g.

2NaNO₃ →2NaNO₂ + O₂

2KNO₃ →2KNO₂ + O₂

4LiNO₃ →2MgO + 4 NO₂ + O₂

2Mg (NO₃)₂ →2MgO + 4NO₂ + O₂

(b) Carbonates of group 1 elements are soluble in water except Li₂CO₃ They are also thermally stable except Li₂CO₃.

Li₂CO₃ →Li₂O + CO₂
Group 2 carbonates are insoluble in water because their lattice energy is higher than hydration energy.
Thermal stability of carbonates of group 2 increases down the group because lattice energy goes on increasing due to increase in ionic character.

(c) Sulphates of group 1 are soluble in water except Li₂SO₄. They are thermally stable.
Solubility of sulphates of group 2 decreases down the group because Lattice energy dominates over hydration energy.
Sulphates of group 2 elements are thermally stable and increasing down the group due to increases in Lattice energy.