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SS3: CHEMISTRY - 2ND TERM

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  1. Quality of Petrol (Octane Number)| Week 1
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    1 Quiz
  2. Natural Gas | Week 2
    3 Topics
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    1 Quiz
  3. Introduction to Metals | Week 3
    3 Topics
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    1 Quiz
  4. The Alkali Metals | Week 4
    4 Topics
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    1 Quiz
  5. Alkaline Earth Metals | Week 5
    4 Topics
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    1 Quiz
  6. Aluminium & Tin | Week 6
    3 Topics
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    1 Quiz
  7. Transition Metals of the First Series | Week 7
    4 Topics
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    1 Quiz
  8. Ethical, Legal & Social Issues | Week 8
    3 Topics
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    1 Quiz
  9. Fats & Oils - Soaps & Detergents | Week 9
    4 Topics
  10. Giant Molecules | Week 10
    6 Topics



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Some Important compounds of calcium are:

1. Calcium oxide or Quicklime (CaO)
2. Calcium hydroxide or Slaked lime  (Ca(OH)2)
3. Calcium Tetraoxosulphate (VI), CaSO4
4. Calcium Trioxonitrate (V), Ca(NO3)2
5. Calcium Sulphate or Plaster of Paris, CaSO4.2H2O or \( \scriptsize CaSO_4.\normalsize \frac{1}{2} \scriptsize H_2 O \)

Calcium compounds are of great economic importance, especially in extraction of metals and in the building industry.

Calcium Oxide:

Preparation of Quick Lime:

Calcium oxide, CaO, is commonly called quicklime. Calcium oxide is prepared by the calcination process. Limestone i.e. calcium trioxocarbonate (IV) is heated to a temperature between 900oC and 1300oC in Kilns and it decomposes to quicklime and carbon dioxide. The kilns have steel shells line with refracting bricks. CaO is removed from the bottom of the Kiln as it is formed.

CaCO3(s)\( \scriptsize \overset{900^oC}{\rightarrow}\) CaO(s) + CO2(g)

Properties of Quick Lime:

1. CaO is a white amorphous solid.

2. It has a high melting point of 2600oC.

3. It can withstand very high temperatures.

4. It is highly stable and even fusion cannot decompose it.

5. It is very hygroscopic. It is used to dry ammonia gas.

Chemical Properties:

1. When water is added to CaO, it cracks to form a white powder. This process is accompanied by the liberation of a lot of heat. This is called slaking of lime and the end product is calcium hydroxide, Ca(OH)2, commonly known as slaked lime.

CaO(s) + H2O(l) \( \rightarrow\) Ca(OH)2(s)

2. Calcium oxide is a basic oxide. It can react with acids to give calcium salts.

3. It forms silicates and phosphates with acidic oxides like silicon dioxide and phosphorus pentoxide. This property makes lime useful as a flux in metallurgy to remove impurities.

4. Calcium oxide reacts with ammonium salts to liberate ammonia gas.

5. Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2000 °C.

CaO(s) + 3C(s)→ CaC2(s) + CO(g)

The major industrial use of calcium carbide, CaC2, is in the production of acetylene.

Uses of CaO:

  1. It is used in making mortar and plaster.
  2. It is used for medicinal purposes, insecticides and plant and animal food.
  3. It is used as a laboratory reagent for gas absorption, precipitation, dehydration etc.
  4. It is used in the manufacture of paper, steel and cement. It is also used in the preparation of calcium carbide, basic calcium trioxonitrate (V).
  5. It can be used for softening hard water and in the recovery of ammonia (by-product of Solvay process).
  6. It finds enormous use in the manufacture of soap, rubber, varnish, refractories and lime bricks.

Calcium Tetraoxosulphate (VI), CaSO4

Calcium tetraoxosulphate (VI), CaSO4 is found in nature as anhydrite, CaSO4, and gypsum, CaSO4.2H2O. It may be prepared in the laboratory by the reaction between a soluble calcium salt with sodium tetraoxosulphate (VI) solution. The CaSO4 formed is only slightly soluble in water and it comes out as a white precipitate.

CaCl2(aq) + Na2SO4(aq) \( \rightarrow\) CaSO4(s) + 2NaCl(aq)

Calcium tetraoxosulphate (VI) causes permanent hardness of water. 

Calcium tetraoxosulphate (VI) is used in the making compounds such as tetraoxosulphate (VI) acid and ammonium tetraoxosulphate (VI).

Plaster of Paris:

Calcium tetraoxosulphate (VI) with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of Paris.

Preparation of Plaster of Paris:

Plaster of Paris is prepared by heating gypsum (CaSO4.2H2O) at 120°C in rotary kilns, where it gets partially dehydrated. The temperature should be kept below 140°C otherwise further dehydration will take place and the setting property of the plaster will be partially reduced.

Properties of Plaster of Paris:

It is a white powder. When mixed with water (1/3 of its mass), it evolves heat and quickly sets to a hard porous mass within 5 to 15 minutes. During setting, a slight expansion (about 1%) in volume occurs so that it fills the mould completely and takes a sharp impression. 

Uses of Plaster of Paris

  1. In surgery for setting broken or fractured bones
  2. For making casts for statues, in dentistry, for surgical instruments, and toys, etc.
  3. In making blackboard chalks, and statues
  4. In construction industry

Calcium Trioxonitrate (V), Ca(NO3)2

Calcium trioxonitrate (V), Ca(NO3)2 is prepared in the laboratory by the reaction between CaCO3 or CaO with trioxonitrate (V) acid.

CaCO3(s) + 2HNO3(aq) →  Ca(NO3)2(aq) + CO2(g) + H2O(l)

It can also be prepared from an aqueous solution of ammonium nitrate, and calcium hydroxide:

2NH4NO3 + Ca(OH)2    →   Ca(NO3)2 + 2NH4OH

Calcium trioxonitrate (V) decomposes on heating to release nitrogen (IV) oxide. 

2Ca(NO3)2    →    2CaO + 4NO2 + O2 

Calcium trioxonitrate (V) is used in making fertilizers.

Calcium Chloride, CaCl2:

Calcium chloride is found in seawater and soil water. It is prepared by the action of hydrochloric acid on calcium trioxocarbonate(IV).

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

The crystals of CaCl2 are very deliquescent and white.

Calcium chloride is used as a drying agent for all gases except ammonia.

The anhydrous salt of CaCl2 is used in desiccators.

Calcium Trioxocarbonate(IV), CaCO3

Calcium trioxocarbonate(IV), CaCO3 occurs abundantly naturally as limestone, chalk and marble.

limestone - sedimentary rock
Limestone.

It is also found in coastal caves as stalagmites (deposits of CaCO3 which grow upwards from the floor of the cave to its top). and stalactites (deposits of CaCO3 which grow downwards from the top of the cave to its floor).

stalagmite
Stalagmites.
Stalactite
Stalactite.

It is also an important constituent in the bones of animals, in the external skeleton of marine organisms. It is found in natural ores, such as calcite, dolomite and Iceland spar.

CaCO3 can be produced in the laboratory as a precipitate when trioxocarbonate(IV), Na2CO3 solution is added to a solution of Calcium chloride, CaCl2.

Na2CO3(aq) + CaCl2(aq) → CaCO3(s) + 2NaCl(aq)

Properties of Calcium Trioxocarbonate(IV)

Below are properties shown by calcium trioxocarbonate(IV)

1. It is a white solid which is insoluble in pure distilled water.

2. It dissolves in water that contains dissolved carbon(IV)oxide, CO2 , to form calcium hydrogen tri-oxocarbonate(IV)

CaCO3(s) + H2O(l) + CO2(g)  → Ca(HCO3)2(aq)

The presence of calcium hydrogen trioxocarbonate(IV), Ca(HCO3)2, is the cause of temporary hardness in water.

3. Calcium Trioxocarbonate(IV) decomposes to give calcium oxide and carbon (IV) oxide, when strongly heated.

4. The action of dilute hydrochloric acid on CaCO3 liberates. CO2

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

Uses of Trioxocarbonate(IV)

Trioxocarbonate(IV) is useful in the following ways:

1. Limestone is a major raw material used in making sodium trioxo-carbonate(IV), glass, steel, quicklime and cement.

2. Marble and limestone are used as building materials.

4. Finely ground limestone is used in neutralizing excess acid in acidic soils.

5. In the extraction of iron. Calcium oxide is provided by limestone which is used to remove impurities as slag.

6. As building materials.

7. In the manufacture of pigments, putty and pap.

8. Cement is mixed with sand and gravel to form concrete, which is an important building material because of its hardness and strength.

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