Hydrogen and S-Block Element: Chemical Properties of Alkaline Earth Metals (For CBSE, ICSE, IAS, NET, NRA 2022)

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Chemical Properties of Alkaline Earth Metals

Reactivity and E° Values

  • These metals are electropositive and are strong reducing agents.
  • The near constancy of the E° values for group 2 metal is similar to group 1.

Oxides

The alkaline earth metals burn in oxygen forming the ionic oxides of the type where stands for alkaline earth metals except which form peroxide.

Hydrides

The alkaline earth metals combine with hydrogen to form hydrides of general formula .

Reaction with Water

  • The alkaline earth metals react with water to liberate hydrogen.
  • Be does not react with water or steam even at red heat and does not get oxidized in air below .

react with cold water with increasing vigour.

Halides

All the alkaline earth metals combine directly with the halogens at appropriate temperature forming halides, where stands for alkaline earth metals.

Solubility and Stability of Carbonates and Sulphates

Carbonates

  • The carbonates of alkaline earth metals are sparingly soluble in water.
  • Thermal stability is increase with increase in the size of the cation and order is shown:

Sulphates

  • The sulphates of alkaline earth metals are stable to heat .
  • The sulphates, and are readily soluble and the solubility decreases from to .
  • The thermal stability of sulphates increases with the increase in the size of cation and order is shown:

Complex Compounds

  • Smaller ions of the group 2 elements form complexes.
  • For example, chlorophyll is a complex compound of magnesium.

Calcium Oxide

Manufacture of

(quick lime) is manufactured in enormous quantities by roasting in lime Kiln.

reacts exothermally with water, forming hydroxide called slaked lime

Calcium Carbonate

  • occurs in two different crystalline forms, calcite and aragonite.
  • Calcite is the more stable and Aragonite is a metastable form.
  • Aragonite can be made in the laboratory by precipitating from a hot solution.

Uses of Lime

  • In steel making to remove phosphates and silicates as slag.
  • By mixing with and alumina or clay to make cement.
  • For making glass.
  • For ‘softening’ water.
  • To make .
  • To make slaked lime by treatment with water.
  • It is used in the lime-soda process, converting to or vice versa.

Biological Role of and

  • ions are concentrated in animal cells, and are concentrated in the body fluids outside the cell.
  • is important in chlorophyll, in the green parts of plants.
  • is important in bones and teeth as apatite , and the enamel on teeth as fluorapatite .

Properties and Uses of Sodium Carbonate

  • Sodium carbonate is freely soluble in water and gives an alkaline reaction.
  • It reacts with some salts in solution and precipitate the corresponding carbonates, e. g.

Due to its alkaline reaction in solution, sodium carbonate frequently precipitate basic carbonates, e. g.

Sodium Hydrogen Carbonate

It can be obtained by passing carbon dioxide through a cold concentrated solution of the corresponding carbonate, e. g.

Sodium hydrogen carbonate solution is less alkaline than sodium carbonate solution.

Biological Importance of Sodium and Potassium

  • To keep normal osmotic pressure of body matter and to save many matter from loss.
  • To increase nano muscular.
  • Sodium and potassium salt combine weak acid to give respective extracellular and intracellular matter.

Stability and Solubility of Carbonate and Sulphate

  • The carbonates and sulphates of alkali metals are generally soluble in water and thermally stable.
  • The carbonates are highly stable to heat and melt without decomposing.
  • As the electropositive character increases down the group, the stability of the carbonates increases.
  • Carbonate of lithium is not so stable to heat due to the small size of lithium.

Alkaline Earth Metals

  • An alkaline earth metal atom is smaller in size compared to its adjacent alkali metals.
  • The ease of losing electrons makes the alkaline earth good metals reducing agents.

Occurrence of Alkaline Earth Metal

  • Magnesium is the second most abundant metallic element in the sea, and it also occurs as carnallite in earth crust.
  • Calcium occurs as calcium carbonate (marble, chalk etc) and with magnesium as dolomite .
  • Strontium and barium are rare and are found as carbonates and sulphates.
  • Beryllium is also rare and is found as beryl.

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