In this topic we will discuss about properties , extraction and chemical reaction of group first metals ( lithium, sodium, potassium,rubidium, Cesium, Francium ). Different metal are extracted from their ores. Main ores of metal are given with chemical formula.
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| Group -1 elements |
Extraction of Sodium :
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Sodium |
- Sodium occurs in nature in the form of its salts
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NaCl
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NaNO3
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Na2CO3.NaHCO3.2H2O
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Na3AlF6
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- Sodium metal is extracted by the electrolysis of fused sodium chloride in the presence of calcium chloride and alkali fluorides which themselves do not decompose at the voltage applied but lower the melting point of NaCl from 800° to about 600°C at which the corrossive action of sodium and chlorine is also reduced considerably.
- Chlorine is a valuable by-product.
Physical Properties :
- Sodium is a soft, silvery- white metal.
- It is lighter than water.
- Its density is 0.972 g cm -3.
- It melts at 97.8°C and boils at 883°C.
- It is sufficiently malleable and ductile and, like other metals, is a good conductor of heat and electricity.
Uses of Sodium:
- Sodium is used in the manufacture of a number of chemicals like sodium peroxide, sodium cyanide and sodamide.
- Sodium is largely used in industry for the production of artificial rubber, dyes, drugs, etc.
- In the laboratory, sodium is employed as a reducing agent in the form of sodium amalgam as well as in the synthesis of many organic compounds.
- It is also used for detecting nitrogen, halogens and sulphur in organic compounds.
- It is used in the extraction of boron and silicon.
- Because of its lightness and high thermal conductivity, it is employed for filling exhaust valves of aeroplane engines.
Extraction of Potassium:
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| Potassium |
- Potassium occurs in nature in the form of its salts such as
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KCl.MgCl2.6H2O
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K2SO4.MgSO4.CaSO4.2H2O
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KCl.MgSO4,3H2O
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K2SO4.MgSO4.6H2O
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KNO3
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K2SO4.2MgSO4
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- Potessium metal is not extracted from any of the above salts. It is obtained by heating potassium fluoride with calcium carbide in steel cylinders at about 1000°C.
2KF + CaC2
→ 2K + CaF2 +2C
Properties of Potassium:
- Potassium resembles sodium in its physical as well as chemical properties. However, it is softer and chemically more reactive. Thus, it reacts with water more violently and the heat of reaction is so high that the hydrogen evolved catches fire.
- When burnt in excess of oxygen, it forms the super oxide, KO2 (sodium under similar conditions gives the peroxide, Na2O2).
- Potassium is slightly radioactive owing to the presence of traces of the radioactive isotope, 19K40 Uses.
- Very few uses have been found for metallic potassium. It is occasionally used in photoelectric cells and in the synthesis of organic compounds.
Extraction of Rubidium:
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| Rubidium |
- Rubidium is a scarce element although it occurs fairly widely in nature alongwith other alkali metals.
- Carnallite contains up to 0.04 % of rubidium chloride, RbCl and is probably the most important source of this metal.
- Lepidolite may contain up to about 1 per cent of rubidium.
- Other lithium ores like tryphylite also contain traces of rubidium.
- This metal is extracted either by the electrolysis of fused RbCl or RbOH, or by the reduction of rubidium carbonate or hydroxide by aluminium or magnesium.
Properties of Rubidium :
- Rubidium is a soft white metal with low melting point (38.9°C) and low boiling point (688°C).
- It is more reactive than potassium.
- It catches fire spontaneously in air and reacts vigorously with water.
Extraction of Cesium:
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| Cesium |
- Cesium, like rubidium, is a rare element.
- The main ores of cesium are Pollucite (Cs4 Al4 Si9O26.H2O) which contains about 27 % of cesium.
- Lepidolite, a lithium ore, which contains 0.2 to 0.7 % of cesium.
- Beryl, a beryllium ore, which contains about 3 % of cesium.
- The metal is obtained from Pollucite by heating the mineral with calcium metal at 900°C. About 85% of the cesium formed volatilizes.
- The vapour of the metal are cooled and the crude condensate purified by sublimation in vacuum at 350°-400°C to get the pure metal.
- Cesium metal can also be obtained by the reduction of the hydroxide or the carbonate with Al or Mg in an atmoshphere of hydrogen .
Properties of Cesium:
- Cesium is a soft white metal with very low melting point (28 .7°C).
- When exposed to air, it first melts and then bursts into flame.
- It decomposes cold water with great violence forming the hydroxide CSOH which is the strongest of all the bases.
Preparation of Francium.:
- This element was discovered by Mlle Perry in 1939 who showed that actinium-237 undergoes producing a new element which was named francium (after France).
- Francium is a radioactive element with a half-life period of 21 minutes only. Because of its very short life, chemistry of francium has been studies by radio-chemical methods.
- It is tarnished rapidly on exposure to moist air.
Chemical Properties of
Sodium:
Action of air:
- Sodium is a highly reactive metal. It react with oxygen explosively.
- At first a film of sodium monoxide Na2O is formed which changes readily into sodium hydroxide by the action of moisture and finally into sodium carbonate by the action of carbon dioxide.
4Na +O2 → 2Na2O
Na2O + H2O → 2NaOH
2NaOH +
CO2 → Na2CO3 + H2O
- When heated in a current of air or oxygen it burns forming a mixture of sodium monoxide and sodium peroxide.
- In a free supply of air or oxygen it is completely oxidized to peroxide.
4Na + O2
→ 2Na2O
2Na2O + O2 → 2Na2O2
Action of water:
- Sodium decomposes water very briskly producing hydrogen.
2Na + 2H2O → 2NaOH + H2
Action of acids:
- Sodium, being a strongly electropositive metal, readily reacts with dilute acids and liberates hydrogen.
2Na +2HCI
→ 2NaCI+ H2
Action of hydrogen:
- Sodium combines directly with hydrogen when heated forming electrovalent hydride.
2Na + H2 →2NaH
Action of ammonia:
- Sodium when heated in a current of ammonia gas forms sodamide, NaNH2 .
2Na + 2NH3 → 2NaNH2+ H2
Action with non-metals:
- It combines readily with chlorine, sulphur and phosphorus giving sodium chloride, sulphide and phosphide, respectively.
2Na +Cl2 → 2NaCI
2Na +S
→ Na2S
3Na +P → Na3P
Reducing action:
- Sodium is a strong reducing agent. It reduces many chlorides and oxides.
Al2O3 + 6Na → 2Al +3Na2O
BeCl2+ 2Na → Be +2NaCl
AICI3 +3Na → 3NaCl + Al
Action with alcohol:
- It reacts gently with alcohol liberating hydrogen.
2Na + 2C2H5OH → 2C2H5ONa + H2
