P block

Question 1

why does Al form 3+ ions in its aq solution and B3+ not?

Answer 1

B3= hight ionisation enthalpy to be compensated by lattice and hydration enthalpy while Al forms Al3+ in aq solution due to hydration enthalpy and forms an octahedral complex .

Question 2

What is the hybridisation of anhy AlCl3

Answer 2

sp3 hybridisation and exist as chlorobridged dimer Al2Cl6 ,coord no =4
Al3+ ions form octahedral complex Al[H2O]6 ,coord no =6,hybridisation – sp3d2

Question 3

oxidation state of B in Mg3B2

Answer 3

3-

Question 4

What is the character exhibited by +1 oxi state of grp 13 elements ?

Answer 4

+1 state shows ionic character while +3 oxin state shows covalent character [Fajan’s rule : higher the oxidation number ,more covalent character]

Question 5

How does the order of electronegativity vary down the group?

Answer 5

Ga and In shows higher e negativity than Al and In respectively[due to poor shielding effect of 10 elecrons and 14 f es ]

Question 6

The trend of reducing power down the group of group 13 elements

Answer 6

Reducing power decreases down the group as the standard red potential increases down the group
[Note: Reducing power is inversely proportional to the reduction potential . Oxidising power is directly proportional to the standard red potential ]

Question 7

Define reducing and oxidising power

Answer 7

Reducing power is the ability to act as a reducing agent .i.e., to donate electrons .
Oxidising power– oxidising agent ,helps to gain the electrons .

Question 8

Explain the existence of TlCl3 ,TlBr3 ,TlF3

Answer 8

TlF3 exists while TlCl 3 and TlBr3 decomposes to form their +1 oxidation sates which is more stable due to inert pair effect .

Question 9

Why is BF3 the weakest Lewis acid

Answer 9

e- deficiency is compensated by the shifting of lone pair of F- to B atom by p pi -p pi back bonding , which is possible due to its small size and high e-negativity .

Question 10

Order of Lewis acid strength

Answer 10

BI3 ,BBr3 ,BCl3 ,Bf3 [in the decreasing order ]

Question 11

Bond order calculation without MOT

Answer 11

B.O = total no.of bonds / total no.of resonating structures
B.O of Bf3 = 4/3 =1.33

Question 12

The hybridisation of diborane

Answer 12

sp3

Question 13

the type of bonds seen in diborane and its hybridisation

Answer 13

3 centered 2 electron bond – MOT–2 in no. [even though e- deficient is equally shared ]
2 centered 2 e- bond –4 in no .[based on VSEPR theory }

Question 14

Properties of diborane

Answer 14

Non planar molecule and Lewis acid [e- deficent ]

Question 15

Orthoboric acid and its solubility in water

Answer 15

H3BO3 or B[OH ]3 .sparingly soluble in water but highly soluble in hot water .

Question 16

Preparation of orthoboric acid

Answer 16

Acidyfying aquoeus solution of borax .
[Note ‘ do not use nitric acid as it is a strong oxidising agent ]
Hydrolysis of B compounds

Question 17

Is orthoboric acid a protonic acid ?

Answer 17

Not a protonic acid ,but acts as alewis acid by accepting an electron pair from hydroxyl ion .

Question 18

Ethyl borate test

Answer 18

orthoboric acid heated with ethanol give triethyl borate and water which in produces a green edged flame .

Question 19

Explain the hybridisation and the geometry of orthoboric acisd

Answer 19

hybridisation –sp2 ,triagonal planar in shape .The compound is polymeric due to h bonding and form 2 D sheets with almost hexagonal geometry .

Question 20

Prep methods of diborane

Answer 20

Heating BF3 with LiAlH4
NaBH4 + I2 in presence of diglyme
Commercial prep –BF3 with NaH

Question 21

Properties of borane

Answer 21

Highly toxic gas and colourless
readily burns in air
Hydrolysis in water gives orthoboric acid .
undergo cleavage reaction with Lewis bases to form borane adducts .

Question 22

Inorganic benzene and its synonymns and its method of prep and its properties

Answer 22

Borazole ,borazine .
diborane at high temperatures reacted with ammonia .
3 pi bonds and 12 sigma bonds
Inorganic benzene is more reactive than benzene becoz B3N3H6 is polar while benzene is non polar in nature

Question 23

The compounds that help in symmetric and non symmetric cleavage of borane

Answer 23

Symmetric cleavage of borane –pyrridine ,Carbon monoxide and tert amine .
Asymmetric cleavage by ammonia ,primary amine , sec amine ,Tetra hydrofuran and

Question 24

Reaction of B and Al with air and N

Answer 24

with air –metal oxides of the form E2O3
with N –metal nitrides of the form EN .

Question 25

Borax or tincal or sodium tetraborate decahydrate

Answer 25

water of crystallisation –8
has 4 units–tetranuclear unit .
2 units sp3 hybridised and other 2 units sp2 hybridised

Question 26

Prep of borax

Answer 26

From colemnite and Na2CO3
orthoboric acid + Na2CO3

Question 27

Properties of borax

Answer 27

Removal of hardness of water
Borax bead test to identify the transitional metal oxide
Co–blue
Cu– blue
Cr– green
Mn –pink
Ni –brown

Question 28

test for borax and boric acid

Answer 28

borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]

Question 28

test for borax and boric acid

Answer 28

borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]

Question 28

test for borax and boric acid

Answer 28

borax +sulphuric acid = boric acid
boric acid + ethanol =tri ethyl borate [green edged flame ]

Question 29

Uses of Al

Answer 29

Bright silvery white metal with tensile strength ,thermal and electrical conductivity
Al is a reducing agent
Al doesnot react with conc HNO3 ,but react with HCl and H2SO4 .
Al –twice the conductivity to that of Cu .
Al forms both ionic and covalent bonds .

Question 30

Uses of B

Answer 30

B fibres are used to prepares bu;;et proof vests .
Light composite material for aircrafts
B has 10 isotopes
B has the ability to absorb neutrons and thus used in nuclear reactors as control rods .