4 . ALKALINE EARTH METALS
1. Why does ionization energy of group IIA
elements decrease from Be to Ra ?
A. The atomic number and size increases from Be to
Ra. The attraction force between the nucleus and
the outermost electrons decreases. Hence it is
easy to remove the electron from outermost shell.
So the ionization energy of group IIA elements
decreases from Be to Ra.
2. Name two ores of Magnesium?
A. The ores of Magnesium: Magnasite (MgCO3) ,
Carnalite (MgCl2.KCl.6H2O)
3. Write the general electronic configuration of
alkaline earth metals?
A. The general electronic configuration of alkaline
earth metals is [ Inert gas ]ns2
4. Why do you add KCl and NaCl to MgCl2 during
Mg extraction?
A. (i) to lower the melting point
(ii) to increase the conductivity of electrolyte,
we add KCl and NaCl to MgCl2 during Mg extraction
5. What are the electrodes used in the magnesium
extraction?
A. The electrodes used in the magnesium extraction:
(i) Iron pot is used as Cathode.
(ii) Graphite rod is used as Anode.
6. Write the electrode reactions during Mg
extraction ?
A. The electrode reactions during Mg extraction:
MgCl2  Mg+2 + 2ClAt Cathode: Mg+2 + 2e-  Mg
At Anode :
2Cl-  Cl2 + 2eMgCl2  Mg + Cl2
7. Write the chemical formula of
(i) Magnasite and (ii) Carnalite?
A. (i) Magnasite (MgCO3),(ii)Carnalite(MgCl2.KCl.6H2O)
8. Which metals are present in Dolomite?
A. Formula of Dolomite is CaCO3.MgCO3
The metals present in Dolomite are calcium (Ca)
and Magnesium (Mg)
9. How many water molecule are present in
Epsomsalt?
A. Formula of Epsomsalt is MgSO4.7H2O
The water molecules present in Epsomsalt are 7.
10. Name the group IIA elements?
A. Beryllium (Be), Magnesium (Mg), Calcium (Ca),
Strontium (Sr), Barium (Ba), Radium (Ra) are the
group IIA elements. They are also called as
alkaline earth metals.
11. Write the reactions of group IIA elements with
(i) Oxygen (ii) Hydrogen (iii) Chlorine and
(iv) Water ?
A. The reactions of group IIA elements:
i)Reaction with Oxygen: All the group IIA
elements burn in oxygen to form oxides of
formula MO.
2M + O2  2MO (here M= Be, Mg, Ca, Sr, Ba)
Beryllium is reactive with oxygen when taken in
bulk and as powder at 6000C.
ii) Reaction with Hydrogen: All the group IIA
elements except Beryllium react with hydrogen to
form hydrides of formula MH2.
M + H2  MH2 (here M= Mg, Ca, Sr, Ba )
BeH2 is prepared by reducing BeCl2 with LiAlH4.
2BeCl2 + LiAlH4  2BeH2 + LiCl + AlCl3
iii)Reaction with Chlorine: All the group IIA
elements react with chlorine to form chlorides of
formula MCl2.
M + Cl2  MCl2 (here M= Be, Mg, Ca, Sr, Ba)
iv)Reaction with Water: All the group IIA
elements reacts with water to form hydroxides of
formula M(OH)2.
M + 2H2O  M(OH)2 + H2 (hereM=Mg,Ca,Sr,Ba)
Beryllium does not react with water. Magnesium
react with hot water and cold water.
12. Describe the method of extraction of
Magnesium from its ore?
A . The electrolytic method of extraction of
magnesium from its ore involves in two steps.
They are (i) Preparation of anhydrous MgCl2.
(ii) Electrolysis of anhydrous MgCl2.
(i) Preparation of anhydrous MgCl2: Magnasite
(MgCO3) is heated in the presence of air to
4500C. It decomposes to magnesium oxide.
MgCO3  MgO + CO2↑
The resultant MgO is mixed with carbon powder
and heated to 10000C in a flow of Chlorine gas.
It gives magnesium chloride and carbon
monoxide.
MgO + Cl2 + C  MgCl2 + CO↑
(ii) Electrolysis of anhydrous MgCl2: In this process
MgCl2 is mixed with Nacl and KCl. It will lower
the melting point and increase the conductivity of
the electrolyte. In this electrolysis process Iron
pot is used as Cathode and Graphite rod is used
as Anode. A Graphite rod enclosed in a
porcelain tube is dipped into the electrolyte. The
iron vessel is maintained at 7000C by external
heating. During electrolysis, the following
reactions take place.
MgCl2  Mg+2 + 2ClAt Cathode: Mg+2 + 2e-  Mg
At Anode :
2Cl-  Cl2 + 2eMgCl2  Mg + Cl2
Chlorine gas is liberated at anode escapes
through the porcelain tube. Magnesium formed at
cathode and floats on the electrolyte as its density
is less. A steam of coal gas is passed over floating
magnesium to prevent oxidation. Floating
magnesium is removed at regular intervals. The
magnesium thus obtained will be 99.9% pure.
13. Draw the chart showing the extraction of
magnesium from its ore?
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