S block elements Alkali metals alkaline earth metals sodium chloride sodium hydroxide sodium carbonate sodium bicarbonate Gypsom Plaster of paris Bleaching powder

1. S-BLOCK
ELEMENTS
Chemistry XII
Sidra Ansari

2. OCCURRENCE
AND
EXTRACTION OF
METALS
a) Alkali Metals
b) Alkaline Earth Metals

3. ALKALI METALS
IA group metals are reactive
Alkali metals are found in variety of Stable compounds
Most abundant are Sodium and Potassium
Usually extracted by electrolysis of fused salts i.e.
Chlorides
Presentation title 3
SODIUM
POTASSIUM

4. DOWN’S PROCESS – MANUFACTURE OF
SODIUM METAL
Sodium sis prepared by the electrolysis of fused sodium
chloride NaCl
CaCl2 is added to reduce the melting point of NaCl from
8000 C to 6000 C
The Electrolysis is carried out in a Down’s Cell
The process involves the reduction of Na+ ions at cathode
Presentation title 4

5. DOWN’S CELL
Iron cell lined with fire bricks
Anode is Graphite present in center
Cathode is made up of Iron which surrounds the anode
An iron gauze diaphragm separates the two electrodes –
this is to keep the molten Na away which floats at the top
of Cathode from the Chlorine gas formed at anode
Presentation title 5

6. Presentation title 6

7. CELL REACTIONS
Mixture of NaCl and CaCl2 is electrolyzed
Na+ ions are reduced at cathode and forms Na metal
Na+ + e-  Na
Cl- ions are oxidized at anode and chlorine gas is produced
2Cl-  Cl2 + 2e-
Over All Reaction
2Na+ + 2e-  2Na (Cathode)
2Cl-  Cl2 + 2e- (Anode)
2Na+ + 2Cl-  2Na + Cl2
Some Ca+2 ions are also reduced to give Ca metal which is
more denser than Na metal so it can be separated easily
Presentation title 7

8. ALKALINE EARTH
METALS
Magnessium Metal
Carnalite double Salt MgCl2KCl.6H2O
Magnesite MgCO3
Dolomite MgCO3 CaCO3
Presentation title 8

9. EXTRACTION OF MAGNESIUM
Direct electrolysis of fused carnalite
A mixture of chlorides can be obtained by heating the
carbonate ores and heating resulting oxides with carbon
and chlorine
MgCO3  MgO + CO2
MgO + C + Cl2  MgCl2 + CO
MgCl2 from sea water can be precipitated as Mg(OH)2 by
adding slaked lime
MgCl2 + Ca(OH)2  Mg(OH)2 + CaCl2
Mg(OH)2 is heated to obtain MgO which can be converted
to Magnesium Chloride
MgO + C + Cl2  MgCl2 + CO
Presentation title 9

10. EXTRACTION OF CALCIUM
Ca is obtained by electrolysis of fused CaCl2 and CaF
Presentation title 10
EXTRACTION OF BARIUM
Barytes BaSO4
Whiterite BaCO3
BaCO3 is converted into chlorides by reaction with HCl
and Ba is obtained by electrolysis

11. INDUSTRIALLY
IMPORTANT COMPOUNDS
OF S-BLOCK ELEMENTS
a) Alkali Metals
i) Sodium Chloride
ii) Sodium Carbonate
iii) Sodium BiCarbonate
iv) Sodium Hydroxide
b) Alkaline Earth Metals
i) Magnesium sulphate
ii) Calcium sulphate

12. SODIUM CHLORIDE - ROCK SALT
Commonly called Table salt
Occurs in nature as Rock Salt
Occurrence in Pakistan – Khewra Salt mines
3 % of sea water is NaCl
Saturated solution which is mined from
underground salt bed – Brine
Brine is used to manufacture Sodium Carbonate
and Sodium Hydroxide
Presentation title 12

13. LOCAL PRODUCTION OF
NACL
Also obtained by evaporation of Sea water
Impurities of Ca and Mg are removed by treating
with Na2CO3 and NaOH
CaCl2 + Na2CO3  CaCO3 + 2NaCl
MgCl2 + 2NaOH  Mg(OH)2 + 2NaCl
Soluble Barium chlorides is used to precipitate
sulphate
The product can be used industrially
Further purification is required for using as Table
salt
Presentation title 13

14. IMPORTANCE OF NACL
• Essential part of daily diet
• Food preservative
• Used in manufacture of following compounds
• Sodium metal,
• chlorine gas,
• sodium hydroxide,
• sodium carbonate,
• sodium hypochlorite (I) ,
• sodium chlorate (V) etc
• Used to glaze earthenware
• Regeneration of water softeners
• Salting out soap
Presentation title 14

15. SODIUM CARBONATE
Manufactured by Ammonia Solvay
Process
Raw Materials :
1. NaCl
2. Lime Stone
3. Ammonia Gas
Presentation title 15

16. AMMONIA SOLVAY
PROCESS
Three Important steps
1. Ammoniation of brine
2. Carbonation of ammoniated brine
3. Conversion to sodium carbonate
Presentation title 16

17. STEP 1 AMMONIATION OF BRINE
• Saturated solution of
NaCl or Brine 28% by
mass is allowed to flow
down ammonia tower
• Mushroom shaped
baffles are present to
control the flow of brine
• Ensures proper
saturation with NH3
17

18. STEP 2 CARBONATION OF AMMONIATED BRINE
• Ammoniated brine is allowed
to trickle down carbonating
tower – Solvay Tower
• Solvay tower is fitted with
baffles plates
• Upward current of CO2
obtained by heating lime
stone
• Baffles plates ensures the
flow of liquid and converts
CO2 into small bubbles
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19. REACTIONS
• Overall reaction is exothermic
• Increase in temperature increases the solubility
of NaHCO3
• To counter this effect lower part of tower is
cooled
• The precipitate of NaHCO3 is removed by
vacuum filtration and washed to free of ammonia
salts
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20. STEP 3 CONVERSION TO SODIUM
CARBONATE
• Sodium Hydrogen carbonate is heated to give
anhydrous Sodium carbonate (Soda Ash)
20
• The CO2 is recycled to the carbonating tower
• Soda Ash is re-crystallized from hot aqueous
solution and yields Sodium carbonate deca
hydrate NaCO3. 10H2O which is known as
Washing Soda

21. SOURCES OF MATERIALS
1. Brine is obtained from natural sources
2. CO2 is obtained by heating limestone
CaCO3  CaO + CO2
3. Ammonia is recovered by solution of
Ammonium chloride left after the removal of
NaHCO3 by vacuum filtration. It is done by
steam heating the solution with quick lime
CaO + H2O  Ca(OH)2
2NH4Cl + Ca(OH)2  CaCl2 + 2H2O + 2NH3
Presentation title 21

22. USES OF SODIUM CARBONATE
1. Manufacture of glass and water glass. Water
glass is made by fusing sand with sodium
carbonate
Na2CO3 + SiO2  Na2SiO3 + CO2
The ordinary glass is manufactured by fusing
mixture of sand, calcium carbonate and
anhydrous sodium carbonate
Presentation title 22

23. USES OF SODIUM CARBONATE
2. Washing soda is used as water softener as it
precipitates calcium ions from water as
carbonates
Ca+2 + Na2CO3  CaCO3 + 2Na+
3. Sodium carbonate is used in making of soap,
paper, detergents and chemicals such as NaOH
Presentation title 23

24. SODIUM HYDROGEN CARBONATE
Commonly known as baking soda
Commercially produced by treating
saturated sodium carbonate solution with
carbon dioxide
Na2CO3 + H2O + CO2  2NaHCO3
Presentation title 24

25. USES OF SODIUM HYDROGEN
CARBONATE
Used as baking powder
Medicines
Antiacids
Presentation title 25

26. SODIUM HYDROXIDE
Important industrial chemical
Caustic to touch
Causes painful burns
Common Name Caustic Soda
Chemical Formula NaOH
Molecular Weight 40 g/mol
Manufactured by Castner-Kellner’s Process
Presentation title 26

27. CASTNER – KELLNER’S PROCESS
Construction of Cell
• Electrolyte 25% w/w
solution of NaCl
• Anode: Titanium plates
• Cathode: Steam of flowing
mercury
• Denuder Chamber packed
with graphite blocks
Presentation title 27

28. CASTNER – KELLNER’S PROCESS
Working of cell:
NaCl dissociates into Na+ and Cl- ions in
aqueous solution
2NaCl  2Na+ + 2Cl-
At Anode:
Chloride ions goes towards anode to liberate
Chlorine gas
2Cl-  Cl2 + 2e-
At Cathode:
Na+ discharged over flowing mercury
cathode surface and forms an amalgam
2Na+ + 2e-  2Na
Na + Hg  Na/Hg
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29. CASTNER – KELLNER’S PROCESS
Working of cell:
the Hg/Na amalgam is sent to Denuder
chamber where Na reacts with Water
2Na/Hg + 2H2O  2NaOH + H2 + Hg
The Hg is recycled to dissolve more Na
The solution which flows out from denuder is
a solution of NaOH which is evaporated to
dryness.
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30. WHY HYDROGEN GAS IS NOT
DISCHARGED AT CATHODE?
• In ordinary process of electrolysis if aqueous
solution of NaCl H2 and Cl2 are liberated at
cathode and anode respectively as H+ ions are
more easily discharged than Na+ions.
• In Castner – Kellner process, H+ ions are not
easily discharged due to high voltage of H+ ions.
• Denuder chamber is packed with graphite blocks
as Hydrogen is easily liberated over graphite
surface
Presentation title 30

31. ADVANTAGES OF CASTNER – KELLNER’S
PROCESS
• Efficient process
• Product is of high purity
• Possible reaction between NaOH and Cl2 is
avoided by collecting NaOH and Cl2 in
separate chambers
Presentation title 31

32. DISADVANTAGES OF CASTNER – KELLNER’S
PROCESS
• Large quantity of electricity is used
• Mercury vapors escapes out in the
surrounding
• Mercury vapors may contaminate sea water
resulting in polluting food chain
• The use of this process is banned and
replaced by Gibb’s diaphragm cell process
which doesn’t use mercury.
Presentation title 32

33. PHYSICAL PROPERTIES OF SODIUM
HYDROXIDE
• White Color
• Deliquescent solid
• Slightly translucent
• Melting point 322oC
• Decomposes at Melting point
• Highly soluble in water
• Dissolution is highly exothermic
Presentation title 33

34. CHEMICAL PROPERTIES OF SODIUM
HYDROXIDE
1. NaOH is a strong alkali. Fully ionizes to Na+ and OH-
ions
2. Reacts with ammonium salts on warming and
liberates ammonia
3. Precipitates soluble metal hydroxides
Presentation title 34

35. CHEMICAL PROPERTIES OF SODIUM
HYDROXIDE
• Amphoteric hydroxide redissolves in excess of NaOH
forming complex ions
Zn+2 + 2OH- Zn(OH)2
Zn(OH)2 + 2OH-  [Zn(OH)4]-2
Tetrahydroxo zincate (II) ion
Presentation title 35

36. USES OF SODIUM HYDROXIDE
• Used in preparation of various chemicals such as
phosphine, sodium chlorate(I) and sodium chlorate (V)
• Manufacture of soap
• Purification of Bauxite
• Paper making
• Manufacture of petroleum products
• Bleaching and dyeing process
• Production of rayon
Presentation title 36

37. COMPOUNDS OF ALKALINE
EARTH METALS
1. Magnessium Sulphate (Epsom MgSO4 )
• Naturally occur as Kieserite MgSO4.H2O
• Prepared by reaction of acid on magnesium metal,
magnesium oxide, magnesium hydroxide or
magnesium carbonate
Presentation title 37

38. COMPOUNDS OF ALKALINE
EARTH METALS
1. Magnessium Sulphate (Epsom MgSO4 )
• MgSO4.7H2O is commonly called Epsom Salt
• Used as mild purgative
• Soluble in water
• It forms anhydrous magnesium sulphate on heating
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39. COMPOUNDS OF ALKALINE
EARTH METALS
2. Calcium Sulphate (CaSO4 )
• Occurs in nature as anhydride
• Dihydrate form CaSO4.2H2O is known as Gypsum
• Sparingly soluble solid
• Produces permanent hardness in water
• When Gypsum is heated about 100oC it loses some
water and converted into calcium sulphate hemihydrate
(CaSO4 ½ H2O) known as Plaster of Paris
• At higher temperature gypsum loses all water of
crystallization and converted into anhydrous calcium
sulphate
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40. COMPOUNDS OF ALKALINE
EARTH METALS
2. Calcium Sulphate (CaSO4 )
• Uses:
• Source of Sulphur dioxide
• Used in manufacture of sulphuric acid
• Gypsum is used in making of cement
• Plaster of Paris when mixed with water sets in
about 5 minutes to a hard mass
• The setting takes place with expansion
• Used in preparation of molds used in surgery and
castings
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41. COMPOUNDS OF ALKALINE EARTH METALS
3. Bleaching Powder
• Ca(OCl)Cl or CaOCl2
• Prepared by Hasen clever process
• The plant consist of iron cylinders in which chlorine is
brought in contact with slaked lime
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