reasoning questions of P-Block

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.

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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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reasoning questions of P-Block