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7/22/2019 reasoning questions of P-Block
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REASONING QUESTIONS IN P BLOCK ELEMENTS
1. Though nitrogen exhibits +5 oxidation state, it does not form pentahalide.
Give reason.
Ans: Nitrogen valence electronic configuration nsnp!due to absence empt"d# orbitals, it can not extend its valence to 5
. $%!has lo&er boiling point than N%!. 'h"(
Ans: )nli*e N%!, $%!molecules are not associated through h"drogen bonding in
liuid state. That is &h" the boiling point of $%!is lo&er than N%!.
!. 'h" are pentahalides more covalent than trihalides (
Ans: %igher the positive oxidation state of central atom, more &ill be its
$olariing po&er &hich, in turn, increases the covalent character of bond
formed bet&een the central atom and the other atom.
-. 'h" is i%!the strongest reducing agent amongst all the h"drides of
Group 15 elements (
Ans: Among hidres of group 15 from N%!to i%!as sie of central atom
/ncreases 0% bond strength decreases. %ence it act as strong reducing
agent.
5. 'rite the reaction of thermal decomposition of sodium aide.
Ans: NaN! Na + ! N2g3
4. 'h" is Nless reactive at room temperature(
Ans: ue to its high NN bond dissociation energ"
6. 'h" does N%!act as a 7e&is base(
Ans: ue to presence of one lone pair of electron present on Nitrogen
8. 0ention the conditions reuired to maximie the "ield of ammonia.
Ans: 9ptimum $ressure 9ptimum Temperature ;emoval of ammonia b"cooling.
=u2N%!3-?+and this is deep blue in color.
1@. 'h" does N9dimerise (
Ans: ue to presence one odd electron on Nitrogen of N911. 'hat is the covalence of nitrogen in N95(
Ans: =ovalenc" is - because N is bonded &ith - bonds
1. /n &hat &a" can it be proved that $%!is basic in nature(
Ans: $hosphine is &ea*l" basic and li*e ammonia, gives phosphonium
compounds &ith acids e.g.,$%!+ %r $%-r
ue to lone pair on phosphorus atom, $%! is acting as a 7e&is base in
the above reaction.
1!. ond angle in $%-+is higher than that in $%!. 'h"(
Ans: oth are sp! h"bridied. /n $%-+all the four orbital are bonded &hereas
in $%!there is a lone pair of electrons on $, &hich is responsible for lone
$air#bond pair repulsion in $%!reducing the bond angle to less than 1@
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15. 'h" does $=l!fume in moisture(
Ans: $=l!react &ith moisture and gives %=l vapours.
$=l!+ ! %9
%!$9!+ ! %=l 14. Are all the five bonds in $=l5molecule euivalent( Custif" "our ans&er.
Ans: $=l5has a trigonal bip"ramidal structure and the three euatorial
$#=l bonds are euivalent, &hile the t&o axial bonds are different and
longer than euatorial bonds.
16. 'hat happens &hen $=l5is heated(
Ans: $=l!h"drol"ses in the presence of moisture giving fumes of %=l.
$=l!+ ! %9 %!$9!+!%=l
18. 'rite a balanced euation for the h"drol"tic reaction of $=l5in heav" &ater.
Ans: $=l5+ 9 $9=l!+ =l
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29. 'h" does 9!act as a po&erful oxidiing agent(
Ans: ue to the ease &ith &hich it liberates atoms of nascent ox"gen 29! 9 + 93,it acts as a po&erful oxidising agent.
30. %o& is 9!estimated uantitativel"(
Ans: 'hen oone reacts &ith an excess of potassium iodide solution buffered
&ith a borate buffer 2p%
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electron to acuire noble gas electronic configuration.
!
43. Bea is the greatest source of some halogens. =omment.
Ans: Larious minerals of halogens from soil are soluble in river &ater hence sea
gets large amount of halogens in the dissolved form.
--. 'rite the balanced chemical euation for the reaction of =l &ith hot and
=oncentrated Na9%. /s this reaction a disproportionate reaction( Custif".
Ans: !=l+ 4Na9% 5Na=l + Na=l9!+ !%9
Mes, chlorine from ero oxidation state is changed to D1 and +5
oxidation states.
-5. 'hen %=l reacts &ith finel" po&dered iron, it forms ferrous chloride and
not ferric chloride. 'h"(
Ans: /ts reaction &ith iron produces %.
Ie + %=l Ie=l+ %
7iberation of h"drogen prevents the formation of ferric chloride.
-4. educe the molecular shape of rI!on the basis of LBE$; theor".
lp and ! bp as LB$E; theor" it has trigonal bip"ram"dal shape.
-6. 'h" is /=l more reactive than /(
Ans: /n general, interhalogen compounds are more reactive than halogens due
to &ea*er D1bonding than D bond. Thus, /=l is more reactive than /.
-8. 'h" are the elements of Group 18 *no&n as noble gases (
Ans: The elements present in Group 18 have their valence shell orbital
completel" filled and, therefore, react &ith a fe& elements onl" undercertain conditions. Therefore, the" are no& *no&n as noble gases.
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-
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2or phosphoric acid3 and phosphine.
45. =an $=l5act as an oxidiing as &ell as a reducing agent( Custif".
Ans: /n $=l5oxidation state of $ is +5, it can not increase its oxidation
state more than it hence it can not act as reducing agent. ut it can
change its oxidation state to +! and act as oxidiing agent.44. 'h" is diox"gen a gas but sulphur a solid(
Ans: ue to small sie 9x"gen can form multiple bonds &here as B canQt hence
B bond &ith B8molecule and exist in solid.
46. Kno&ing the electron gain enthalp" values for 9 9D and 9 9Das D1-1
And 6@ *C molD1 respectivel", ho& can "ou account for the formation of a
7arge number of oxides having 9#species and not 9D(
Ans: %igher second electron gain enthalp" is compensated b" high h"dration
energ" and more lattice energ".
48. 'h" are halogens strong oxidiing agents(
Ans: Bince halogens are having high electron gain enthalp" the" act as strong
oxidiing agents.
4
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et&een lone pairs of t&o I atoms of Imolecule.
2ii3 %IR%rR%=lR%/ as atomic sie increases from I to / bond strength
decreases and acidit" increases.
2iii3 i%!RBb%!RAs%!R$%!RN%!as sie increases from N to i electron
densit" decreases and basesit" decreases.
65. Give the formula and describe the structure of a noble gas species &hich is isostructural &ith:
2i3 /=l-#2ii3 /r
# 2iii3 r9!
#
Ans: 2i3 e=l- 2 lp + - bp O4, sp!doccupied &ith lone pairs over all
geometr" is suare planar3
2ii3 er 2bp+-lpO4, sp!doccupied &ith lone pairs over all
geometr" is linear3
2iii3 e9! 2!bp+ 1lpO-, sp!occupied b" one lone pair, p"ramidal shape.
64. 'h" do noble gases have comparativel" large atomic sies(
Ans: Noble gases exist as mono atomic gases, there is no overlapping of atomic
orbitals li*e in other compounds. %ere atomic radius is considered as
vandr&aalQs radii. %ence atomic radii are comparativel" large.66. 'h" does the reactivit" of nitrogen differ from phosphorus(
Ans: ue to small sie, multiple bond formation, absence of empt" d# orbitals.
68. The increase in the atomic sie from As to i is small as compare from
N to $, Sustif" "our ans&er.
Ans: There is a considerable increase in covalent radius
from N to $. %o&ever, from As to i onl" a small increase in covalent
radius is observed. This is due to the presence of completel" filled d andor
f orbitals in heavier members.
68. 'h" N differs in its properties as compare &ith rest of elements of goup
15.
Ans: Nitrogen differs from the rest of the members of this group due to
its smaller sie, high electronegativit", high ionisation enthalp" and
non#availabilit" of d orbitals.
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8-. 'h" ox"gen sho&s anomalous behavior as compare &ith its congeners (
Ans: /t is due to its small sie, %igh Electro negativit", 0ore /oniation
Enthalp" and absence of empt" d# orbitals.
85. The stabilit" of + 4 oxidation state decreases do&n the group and stabilit" of + - oxidation state increase in group 14, Explain.
Ans: /t is due to inert pair effect.85. Al9!is amphoteric explain &ith chemical reactions.
Ans:
84. uring dilution of sulphuric acid it must be added to &ater but &ater
should not be added to acid. Explain(
Ans: /t dissolves in &ater &ith the evolution of a large uantit" of heat. %ence,
care must be ta*en &hile preparing sulphuric acid solution from
concentrated sulphuric acid. The concentrated acid must be added slo&l"
into &ater &ith constant stirring.
86. 9xidising abilit" of halogens is I=lr/give reason.
Ans: The decreasing oxidising abilit" of the halogens in aueous solutiono&n the group is evident from their standard electrode potentials
&hich are dependent on the parameters indicated belo&:
88. /onic character of metal halides decreases from 0I to 0/. Give reason.
Ans: The ionic character of the halides decreases in the order
0I 0=l 0r 0/ &here 0 is a monovalent metal.
As electronegetivit"Electron gain enthalp" decreases /onic characterincreases.
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Ler" pure nitrogen can be obtained b" the thermal decomposition of sodium
or barium aide.
At higher temperatures, it directl" combines &ith some metals to form
predominantl" ionic nitrides and &ith non#metals, covalent nitrides. A fe&
t"pical reactions are:
/t combines &ith h"drogen at about 66! K in the presence of a catal"st
2%aberQs $rocess3 to form ammonia:
initrogen combines &ith diox"gen onl" at ver" high temperature 2at about
@@@ K3 to form nitric oxide, N9.
Ammonia is present in small uantities in air and soil &here it is formed b"the deca" of nitrogenous organic matter e.g., urea.
9n a small scale ammonia is obtained from ammonium salts &hich
decompose &hen treated &ith caustic soda or lime.
9n a large scale, ammonia is manufactured b" %aberQs process.
/t forms ammonium salts &ith acids, e.g., N%-=l, 2N%-3B9-, etc. As a &ea*
base, it precipitates the h"droxides of man" metals from their salt solutions.Ior example,
Ammonia donate lone pair to the metal ions and form different complex
compounds, b" this metals ions can be detected.
Nitrogen 2/3 9xide >Nitrous 9xide? N%-N9! %eat N9 + %9
Nitrogen 2//3 9xide >Nitric 9xide?
NaN9 + IeB9-+ !%B9- Ie2B9-3!+ Na%B9-+ % 9 + N9 Nitrogen 2///3 9xide >di Nitrogen Tri 9xideU N9 + N9- 5@K N9!
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Nitrogen di 9xide >Nitrogen 2/L3 9xide?
$b 2N9!3 46!K -N9 + $b9
Nitrogen 2/L3 9xide >di Nitrogen tetroxide?
Nitrogen 2L3 9xide >di Nitrogen pentoxide? -%N9!+ $-91@
-%!$9!+N95
/n the laborator", nitric acid is prepared b" heating KN9!or NaN9!and
concentrated %B9-in a glass retort.
9n a large scale it is prepared mainl" b" 9st&aldQs process. This method is
based upon catal"tic oxidation of N%!b" atmospheric ox"gen.
Nitric oxide thus formed combines &ith ox"gen giving N9.
Nitrogen dioxide so formed, dissolves in &ater to give %N9!.
=oncentrated nitric acid is a strong oxidiing agent and attac*s most metals
except noble metals such as gold and platinum.
Hinc reacts &ith dilute nitric acid to give N9 and &ith concentrated acid to
give N9.
=oncentrated nitric acid also oxidises nonDmetals and their compounds. /odine
is oxidised to iodic acid, carbon to carbon dioxide, sulphur to %B9-, and
phosphorus to phosphoric acid.
Brown Ring Test: The familiar bro&n ring test for nitrates depends on the
abilit" of Ie+ to reduce nitrates to nitric oxide, &hich reacts &ith Ie +to form
a bro&n coloured complex.
/t dissolves in boiling Na9% solution in an inert atmosphere giving $%!.
/t readil" catches fire in air to give dense &hite fumes of $-91@.
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$hosphine is prepared b" the reaction of calcium phosphide &ith &ater or
dilute %=l.
/n the laborator", it is prepared b" heating &hite phosphorus &ith concentratedNa9% solution in an inert atmosphere of =9.
it is absorbed in %/ to form phosphonium iodide 2$%-/3 &hich on treating
&ith K9% gives off phosphine.
'hen absorbed in copper sulphate or mercuric chloride solution, the
corresponding phosphides are obtained.
$hosphine is &ea*l" basic and li*e ammonia, gives phosphonium compounds
&ith acids e.g.,
/t is obtained b" passing dr" chlorine over heated &hite phosphorus.
/t is also obtained b" the action of thion"l chloride &ith &hite phosphorus.
/t is a colourless oil" liuid and h"drol"ses in the presence of moisture .
/t reacts &ith organic compounds containing D9% group such as =%!=99%,
=%59%.
$hosphorus pentachloride is prepared b" the reaction of &hite phosphorus
&ith excess of dr" chlorine.
$=l5is a "ello&ish &hite po&der and in moist air, it h"drol"ses to $9=l!andfinall" gets converted to phosphoric acid.
'hen heated, it sublimes but decomposes on stronger heating.
/t reacts &ith organic compounds containing D9% group converting them to
chloro derivatives.
Iinel" divided metals on heating &ith $=l5 give corresponding chlorides.
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phosphorous acid on heating disproportionates to give orthophosphoric acid
2or phosphoric acid3 and phosphine.
The acids &hich contain $D% bond have strong reducing properties. Thus,
h"pophosphorous acid is a good reducing agent as it contains t&o $D% bonds
and reduces, for example, AgN9! to metallic silver.
These dimeric halides undergo disproportionation as given belo&:
iox"gen can be obtained in the laborator" b" the follo&ing &a"s:
2i3 " heating ox"gen containing salts such as chlorates, nitrates and
permanganates.
B9combines &ith &ater to give %B9!, an acid.
Al9!reacts &ith acids as &ell as al*alies.
'hen a slo& dr" stream of ox"gen is passed through a silent
electricaldischarge, conversion of ox"gen to oone 21@V3 occurs. The product
is *no&n as oonised ox"gen.
it oxidies lead sulphide to lead sulphate and iodide ions to iodine.
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Nitrogen oxides emitted from the exhaust s"stems of supersonic Set aeroplanes
might be slo&l" depleting the concentration of the oone la"er in the upper
atmosphere.
'hen moist, sulphur dioxide behaves as a reducing agent. Ior example, it
converts iron2///3 ions to iron2//3 ions and decolories acidified potassium
permanganate2L//3 solution
The *e" step in the manufacture of %B9-is the catal"tic oxidation of B9
&ith 9to give B9!in the presence of L95 2catal"st3.
Bulphuric acid, because of its lo& volatilit" can be used to manufacture more
volatile acids from their corresponding salts.
Bulphuric acid removes &ater from organic compoundsF it is evident b" its
charring action on carboh"drates.
metals and non#metals are oxidied b" concentrated sulphuric acid, &hich is
reduced to B9.
/n general, a halogen oxidies halide ions of higher atomic number.
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/Dcan be oxidised b" ox"gen in acidic mediumF Sust the reverse of the reaction
observed &ith fluorine.
$reparation of =hlorine:
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