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grp 13 ....continued

* m.p and b.p of B > Al .why ?

due to small size and efficient packing of boron in crystal lattice

* order of reducing power : Al > Ga > In > Tl . why ?

becoz down the grp , electrode potential increases and reducing power decreases .

* why boric acid (H3BO3) is a monobasic acid even when it contains 3 hydroxl groups ??

boron atom is small in size and has only 6 electrons in its valence shell in boric acid . so it accepts a l.p. of electrons from the oxygen atom of H2O to form a hydrated species .
so the positively charged oxygen atom pulls sigma electrons of O-H bomd towards itself , releasing a proton .

* conc HNO3 can be stored in aluminium containers . why ??

becoz Al on reacting with the acid forms a protective layer of Al2O3 which prevents further reaction between metal and acid .

*AlF3 is more ionic than AlCl3 .why ?

Fluoride ion is smaller than chloride ion and is less polarised by Al3+ to show ionic character .
it is becoz of the same reason that AlF3 has greater m.p than AlCl3

* why all bonds Al -Cl bonds in Al2Cl6 are not equivalent ?

in Al2Cl6 each Al atom forms 3 covalent bonds with three chlorine atoms and one co -ordinate bond with the chlorine atom of another AlCl3 molecule.

* why alumina cannot be reduced by carbon ?

at high temp. alumina reacts with carbon to form aluminium carbide.....

2 Al₂O₃ + 6C ---à Al₄C₃ + 3CO₂

* Sodium carbonate (washing soda should not be kept in Al containers . why ?

Sodium carbonate reacts with water to form sodium hyroxide which in turn will react with the container and hydrogen gas will be evolved .

Na₂CO₃+2H₂O --à 2NaOH + H₂CO₃

Al + 2NaOH + 6H₂O -----à 2Na[ Al (OH ) ₄ ] + 3H₂

_{* why anhydrous AlCl3 cannot be prepared by heating AlCl3.6H2O ?}

_{bcoz hydrated aluminium chloride on heating undergoe hydrolysis to produce Al2O3.}

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