EXTRACTION OF SODIUM AND CALCIUM

 

Week:                   TWO                                      Date:                                                    

Period:                                  Duration: 1 HR 20 MIN.                                                  Average age of learners: 17YEARS

Subject:                                CHEMISTRY                                                                         Class: SS 3

Topic:                                    METALS AND THEIR COMPOUNDS

Sub topic: EXTRACTION OF SODIUM AND CALCIUM

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials: Nail and Aluminium foil

Entry behavior: The students have been familiar with metallic materials.

Behavioural objective: At the end of the lessons the students should be able to:

1.       Mention the main sources of sodium.

2.       Explain the extraction of sodium

3.       Explain the chemical properties of sodium

4.       List some of the general properties of alkaline earth metal

5.       Explain the extraction of calcium

6.       State uses of calcium

CONTENT

SODIUM

Sodium does not occur free in nature because it is too reactive. It occurs mainly as chloride in sea water. Other sources include bromides and iodides. It also occurs in deposit as sodium chloride (rock salt), sodium trioxonitrate(v) and sodium trioxocarbonate(iv).

EXTRACTION OF SODIUM

Sodium is extracted commercially by the electrolysis of molten sodium chloride using the down cell.

Chemistry of the reaction

Fused sodium chloride contain sodium and chloride ions.  NaCl             Na+ + Cl-

At the cathode: The Na+ receive an electron each to become metallic sodium. Hence the Na+ is said to be reduced.  Na+  +  e-              Na (Reduction).

At the anode: The chloride ions give up an electron each to become chlorine atom which then pair up to give gaseous chlorine molecules. Hence, the chloride ion is said to be oxidized.

Cl-          Cl  +  e- (Oxidation)

Cl + Cl               Cl2

PHYSICAL PROPERTIES OF SODIUM

1.       Sodium is a silvery soft solid with a metallic luster.

2.       It has a melting point of 98oC and boiling point of 883oC

3.       It is a good conductor of heat and electricity

4.       It has a density of 0.97gcm-3

CHEMICAL PROPERTIES OF SODIUM

1.REACTION WITH AIR: Na metal tarnishes rapidly when expose to air because it is readily oxidized by atmospheric oxygen to form sodium oxide. 4Na  +  O2              2Na2O.

When heated in plentiful supply of air, sodium burns with a golden yellow flame to form sodium peroxide

2Na + O2             Na2O2

2. REACTION WITH EXCESS COLD WATER: Na reacts vigorously with cold water, releasing a lot of heat.

                2Na(s) + H2O(l)           2NaOH(aq) + H2(g)

3. REACTION WITH ACID: Na react explosively with dilute acids to form hydrogen and a salt.

                2Na + 2HCl            2NaCl(aq) + H2(g)

4. REACTION WITH AMMONIA: Na reacts with ammonia to form sodamide and hydrogen.

                2Na + 2NH3                2NaNH2 + H2

5. REACTION WITH NON-METALS: On heating, sodium combines directly with most non-metals except boron, carbon and nitrogen. 2Na + H2         2NaH;  3Na + P          Na3P [trisodium phosphide (iii)].

Test for sodium ions

Flame test- Na compounds give a golden yellow colour to a non-luminous flame. If a golden yellow cannot be seen through a blue glass, the presence of Na+ in the unknown compound is confirmed.

USES OF SODIUM

1.       It is used in the manufacturing compounds such as NaNH2.

2.       It is used as reducing agent in the extraction of titanium.

3.       Used in sodium vapour lamp.

4.       In the production of lead(iv) tetraethyl which serve as an anti-knock agent in petrol.

5.       It is used as a coolant in nuclear reactor.

THE ALKALINE EARTH METAL

The alkaline earth metals form the second column of the S-block in the periodic table. They are more electronegative but less basic than the alkali metals. The alkaline metals are too reactive to occur free in nature. All the element occurs as trioxocarbonate(iv) and tetraoxosulphate(vi). The familiar elements in this group are magnesium and calcium. Other elements are beryllium, strontium, barium and radium.

PHYSICAL PROPERTIES OF ALKALINE EARTH METAL

1.       They form stable bivalent positive ion by the loose of two valence electrons in the outermost shell.

2.       They are better conductor of heat and electricity that group I elements.

3.       They have high melting points.

4.       They are less soluble compared to group I element.

GENERAL CHEMICAL PROPERTIES OF ALKALINE EARTH METALS

1.       REACTION WITH AIR OR OXYGEN: All metals tarnish in air forming a film of oxide, the speed of the reaction increases from beryllium to barium. In the case of Be and Ba the film of oxide is protective, preventing further reaction from taking place. With other alkaline earth metal, the film of oxide is non-protective so that the reaction proceeds to the completion.

2.       REACTION WITH WATER: Beryllium does not react with water in any form because of the insolubility of its hydroxide. Magnesium react slowly with steam Mg(s) + H2O(g)            MgO(s) + H2(g). generally, the reaction with water increases from beryllium to barium.

3.       AS A REDUCING AGENTS: Alkaline earth metals are all powerful reducing agents. Calcium and magnesium reduce any oxides to their metal. Calcium is more effective as a reducing agent at high temperatures.

4.       REACTION WITH ALKALI: beryllium reacts with NaOH to liberate hydrogen, forming sodium beryllate (ii) in solution. Be(s) + 2NaOH + H2O             Na2Be(OH)4  + H2. Other alkaline earth metals do not react readily. Be(OH)2 is an amphoteric.

CALCIUM (Ca)

Calcium occurs abundantly as trioxocarbonate(iv), CaCO3, in limestone, marble, chalk, calcite and aragonite, it occur as CaSO4 in gypsum and anhydrite and as a double CaCO3, MgCO3 in dolomite. Calcium occurs as CaF2 in fluorspar. Bones and teeth contains CaPO4.

Calcium and magnesium compounds formed by the weathering of rocks are found in soil and in most freshwater as HCO3-, SO42-, and Cl-, causing hardness of water.

EXTRACTION OF CALCIUM

Calcium is extracted by the electrolysis of fused anhydrous CaCl2. In the electrolytic cell, CaF2 is added to lower the melting point from 850oC to 650oC. The mixture is placed in a large crucible, lined on the inside with graphite which serves as the anode of the cells. The cathode is an iron rod which just dips below the surface of the calcium chloride. The CaCl2 is melted and the electrolysis begun. As the electrolysis proceeds metallic calcium is deposited on the cathode. Cl2 is liberated at the anode.

Chemistry of the reaction

CaCl2         Ca2+  + 2Cl-

At the cathode: calcium ion received two electrons each to become reduced to metallic calcium.

Ca2+  + 2e-            Ca

The metallic calcium form deposit on the cathode.

At the anode: the Cl- gives up an electron each to become chlorine atom. Two of the chlorine atoms then combine to form chlorine molecule, which is then liberated.

Cl-              Cl + e- ; Cl + Cl                  Cl2

PHYSICAL PROPERTIES OF CALCIUM

1.       It is a soft silvery-grey metal

2.       It has melting point of 851oC and a boiling point of 1487oC.

3.       Has a density of 1.55gcm-3

4.       It is a good conductor of heat and electricity.

5.       It is malleable and ductile

 

 

CHEMICAL PROPERTIES CALCIUM

I.                    REACTION WITH WATER: Calcium react with cold water and rapidly with warm water to form Ca(OH)2 and H2.  Ca   +  2H2O           Ca(OH)2 + H2

II.                  REACTION WITH ACIDS: Ca + 2HCl               CaCl2  +   H2

III.                REACTION WITH AMMONIA:  3Ca + 2NH3             Ca2N2 + 3H2

USES OF CALCIUM

i.                     Calcium is used in the extraction of uranium.

ii.                   Used as deoxidant in steel casting and copper alloys.

iii.                  Used in the manufacture of CaF2 and CaH2.

iv.                 Used to remove impurities from petroleum.

v.                   Used as dehydrating agent in the preparation of pure ethanol.

PRESENTATION

I.                    The teacher explains the extraction of sodium.

II.                  The teacher states physical and chemical properties of sodium

III.                The students chorus the physical properties of sodium

IV.                The teacher states the general properties of alkaline earth metals

V.                  The teacher explains the extraction of calcium

VI.                The teacher states the uses of calcium

EVALUATION

 The teacher evaluates the lessons by asking the following questions:-

1.       Mention the main sources of sodium.

2.       Explain the extraction of sodium

3.       Explain the chemical properties of sodium

4.       List some of the general properties of alkaline earth metal

5.       Explain the extraction of calcium

6.       State uses of calcium

 ASSIGNMENT

 Considered the following compound: CaO,CaCO3,CaC(OH)2,NaOH.

 (a)         Which of them is used in the manufacture of cement

(b)          Used to detect the presence of carbon (iv) oxide

 (c)          Used to liberate carbon (iv) oxide when dilute acid is added

 (d)         Hygroscopic

(e)          As a dessicant

 (f)          In the production of plaster of paris (POP)

 (g)         To neutralize acid soil

 

 

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