12th Class Chemistry Chapter 4 Group V-A and VI-A Elements Short Question Answers

Nitrogen occurs as N₂ in the atmosphere 80% by volume.Phosphorus occurs in the form of its compounds as phosphates.Arsenic  antimony and bismuth are less abundant.

Nitrogen has two allotropic forms in the solid states i.e. a-nitrogen and B-nitrogen. Phosphorus has six allotropic forms: i) White ii) Red iii) Scarlet iv) a-black iv) B-black vi) violet

Melting points increase from upper to the downward direction except antimony and bismuth.Bismuth has lower melting point than antimony.

Phosphorus has available d-orbitals in its outermost shell.Electrons can be promoted from s-orbital to this d-orbital and five unpaired electrons become avaiable.In this way it can show the valency of five.

P-sub shell has three electrons in the outermost shell of group V-A.This is half-filled.The half-filled orbitals are extra stable.

The oxides having the general formulas M2O3 M2O4and M2O5 are given by the elements of group V-A Anyhow nitrogen can give N2O, and NO as additional oxides which are not given by other elements of this group.

These compounds are:
HNO₃                Nitric acid
H₃PO₄               Phosphoric acid
H₃AsO₄             Aresenic acid
H₃SbO₄             Antimonic acid

Nitrogen is a gas but other members are solids.Nitrogen is diatomic while others are tetratomic.Oxidation states  of nitrogen are +1,+2,+3.+4,+5,-1,-2,-3 while other elements donot show the variety of oxidation states.

Nitrogen give five oxides which are as follows:
N₂O   = Dinitrogen oxide           +1(colourless)
NO    =  Nitrogen oxide              +2(colourless)
N₂O₃ =  Dinitrogen trioxide       +3
N₂O₄ = Nitrogen dioxide            +4(reddish brown)
N₂O₅ = Dinitrogen pentaoxide  +5

N₂O reacts  with carbon sulphur;phosphorus magnesium sodium and copper to give their oxides and nitrogen gas is set free.
C+2N₂O………………………. CO₂ + 2N₂

N₂O has a linear structure and shows resonance.The structure of NO exists in the form of a dimmer.
N=N⁺ – O^–

NO reacts with FeSO₄ to give a black compound.When this black compound is heated,NO gas is released
FeSO₄ + NO………………..FeSO₄.NO
Black ppt.

No oxidizes SO₂ to H₂SO₄.It oxidizes H₂SO₃ and H₂S to S
2NO+So₂+H₂O………….H₂SO₄+N₂O
H₂S + 2NO……………. H₂O + S+N₂O
H₂SO₃+2NO……………… H₂SO₄+N₂O

2Pb(NO₃)₂……………..2PbO+4NO₂+O₂
Cu+4HNO₃………………. Cu(NO₃)₂ + 2NO₂+2H₂O

N₂O₄ is converted to NO through the following sequence of reactions.
N₂O₄…9ᵒC….N₂O₄….22ᵒC.. N₂O₄…140ᵒC…2NO₂…620ᵒc..2NO+O₂
Solid               Liquid              Vapours           Gas                  Gaseous mixture

NO₂ can oxidize H₂S to S,CO to CO₂ FeSO₄ to Fe₂(SO₄)₃ and KI to I₂.
NO₂+H₂S…………………..NO+H₂O+S
NO₂+CO…………………..CO₂+NO
NO₂+2KI…………………. 2KNO₂+I₂.

HNO2 releases atomic oxygen which converts HI to I2,SO2 to H2SO4 SnCI2 to SnCI4 etc.
i) 2HNO2 + 2HI………………I2+2NO+2H2O
ii)2HNO2+SO2……………….H2SO4+2NO
iii)SnCI2+2HCI+2HNO2………………SnCI4+2NO+2H2O

Certain strong oxidizing agents like acidified KmnO₄,acidified K₂Cr₂O₇ and H₂O₂ are reduced by HNO₂.
HNO₂+H₂O₂……………HNO₃+H₂O
HNO₂+Br₂+H₂O…………2HBr+HNO₃
2KmnO₄+3H₂SO₄+5HNO₂…………K₂SO₄+2MnSO₄+5HNO₃+3H₂O

Reactions completes  in four stages:
N₂+O₂…………………. 2NO
2NO+O₂…………………2NO₂
2NO₂+H₂O……………….HNO₂+HNO₃
3HNO₂…………………….HNO₃+2NO+H₂O

With concentrated H₂SO₄ 68% HNO₃ is converted into 98% HNO₃.Water is absorbed by H₂SO₄.To get 100% HNO₃ it is strongly cooled.Pure acid is deposited as colorless crystals at – 42ᵒC.These crystals are melted to get 100% HNO₃.

HNO₃ can oxidize FeSO₄ H₂S HI,SO₂ and sugar.
6FeSO₄+3H₂SO₄+2HNO₃…………….. 3Fe₂(SO₄)₃+2NO+4H₂O
3H₂S+2HNO₃……………….2NO+3S+4H₂O
SO₂+2HNO₃……………………H₂SO₄+2NO₂

When conc.HCI and conc.HNO₃ are mixed in the ratio of 3:1 the mixture is called aqua regia.
HNO₃+3HCI…………………2H₂O+NOCI+CI₂
Au+HNO₃+3HCI…………….AuCI₃+NO+2H₂O

Concentrated nitric acid is a colourless volatile liquid and it fumes strongly in the air.Actually it evolves the NO₂ gas.

Ring test is for NO^–₃ ion in aqueous solution.To the solution add freshly prepared solution of FeSO₄.Then add a few drops of conc.H₂SO₄along the side of the test tube.A brown ring is produced.This is due to FeSO₄ NO.

The important ores of phosphorus are:
Ca₃(PO₄)₂.              = Phosphate rock
Ca₃(PO₄)₂.CaCI₂    = Chlorapatite
3Ca₃(PO₄)₂.CaF₂    = Fluorapatite
It also occurs in plants and animal tissues.Phosphorus is found in seeds,yolks of eggs nerves brain and bone marrow.

White phosphorus is yellowish white substance and is a waxy solid.It is volatile in nature soluble in benzene and CS₂.Its molecules are P₄ and tetrahedral in shape.Red phosphorus is poisonous but less  than that of white phosphorus.It is less reactive  than white phosphorus.It exists in the form of tetrahedral P₄ units to give macro molecules Red.P is prepared from white P in the presence of I₂ or S as a catalyst and heating upto 250ᵒC.

In both molecules the central atom is sp³-hybridized and they have lone pair at the fourth corner.They have pyramidal structures.Anyhow bond angles and bond lengths are different.

The phosphorus halides react with alcohols and carboxylic acids to give alkyl halides and acid halides
3ROH+PCI₃……………..3RCI+H₃PO₃
ROH+PCI₅…………….. RCI+POCI₃.+HCI
3ROOH+PCI₃……………..3RCOCI+H₃PO₃
RCOOH+PCI₅………………ROCI+POCI₃+HCI

Phosphorus gives four different types of oxides.
Phosphorus trioxide         = P₂O₃ or P₄O₆
Phosphorus tetraoxide    = P₂O₄
Phosphorus pentaoxide   = P₂O₅
Phosphorus Peroxide       = PO₃Or P₂O₆

P₂O₃ reacts with water in cold state to give H₃PO₃.In hot state it gives H₃PO₄
P₂O₃+3H₂O……..Cold/Hot………2H₃PO₃
2P₂O₃+6H₂O…………….3H₃PO₄+PH₃

P₂O₅.+H₂O……Cold……….2HPO₃
P₂O₅.+2H₂O…….Normal…H₄P₂O₇.
P₂O₅.+3H₂O……Hot………2H₃PO₄.

P₂O₅.takes up water molecule from various compounds to give HPO₃.
2HNO₃+ P₂O₅……………….2HPO₃+N₂O₅
H₂SO₄+ P₂O₅………………..2HPO₃+SO₃
2CH₃COOH+ P₂O₅…………..(CH₃CO)₂O+2HPO₃
C₂H₅OH+P₂O₅………………C₂H₄+2HPO₃

Some typical oxyacids of phosphorus are as follows:
i) Hypophosphorus acid    = H₃PO₂   +1
ii) Phosphorus acid             = H₃PO₃   +3
iii)Hypophosphoric acid     = H₄P₂O₆  +4
iv)Orthophosphoric acid    = H₃PO₄    +5

The structure of H₃PO₃ shows that one of the hydrogens is directly connected with phosphorus which is not ionizable.So it does not release third hydrogen.Only two hydrogens are ionizable.

H₃PO₃ reduces CuSO₄ .to copper metal AgNO₃+NH₄OH to silver metal.
CuSO₄ . H₃PO₃+H₂O…………….. H₃PO₄ H₂SO₄+Cu
H₃PO₃+ 2AgNO₃+NH₄OH………… H₃PO₄2NH₄NO₃+H₂O+2Ag

When H₃PO₄ is heated at 240ᵒC it given perphosphoric acid and on further heating it finally gives P₂O₅
2 H₃PO₄ ……. 240ᵒC…… H₄PO₇+H₂O

H₄P₂O₇…………316ᵒC……2HPO₃+H₂O
2HPO₃…..600-700ᵒC……P₂O₅+H₂O
Yes one mole of H₃PO₄ consumes three moles of NaOH.

Oxygen is a gas while other family members are solids.Anyhow their melting and boiling points increase down the group.P₆ is a soft substance as compared to Te.

Electronic distribution of sulphur shows that d-orbital is available for the promotion of electrons.So four and six upaired electrons can develop.In this way it increases its oxidation number as +4 and +6.

Oxygen has two non-metallic forms as O₂ and O₃ .Sulphur exists as rhombic monoclinic and plastic sulphur.Se has red and grey both are non-metallic.Te has two forms metallic and non metallic.Po has two metallic forms i.e.a and B.

Oxygen has very small size and high electronegativity.d-orbitals are not available for the promotion of electrons.So oxidation number does not increase.Oxygen is highly electronegative as compared to sulphur.O₂ is a gas at room temperature but sulphur is solid.

It is a 44.6% of earth’s curst.25% of atmosphere by weight is free oxygen.Water contains 89% oxygen by weight.Chalk contains 48% oxygen while SiO₂ has 53% of oxygen by weight.

Sulphur occurs in the form of compounds like galena zinc blend cinabar copper pyrite and iron pyrites.The organic compounds and vegetables products like garlic mustard hair eggs and proteins sulphur in them.

V₂O₅ or Fe₂ O₅  with the little amount of CuO can be used as catalyst.Anyhow Pt.metal supported on MgSO₄ can also be used as a catalyst.

The temperature of 400-500ᵒC is maintained at a pressure of 1 atm.A suitable catalyst like V₂O₅ is used to increase the rate of reaction.

Contact process is superior to lead chamber process for the manufacture  of H₂SO₄ due to following reasons:
i) A purified form of H₂SO₄  is prepared.
ii) Solid catlyst is used like V₂O₅  and Pt.while in the lead chamber process  NO₂ gas is used as a catalyst

SO₃ is dissolved in H₂SO₄ .If SO₃ is dissolved directly in water then a large amount of heat is evolved.This heat gives a dense form of minute particles of H₂SO₄ .These particles do not easily condense down.

H₂SO₄ has a strong affninity for water.It dehydrates oxalic acid  formic acid ethyl alcohol glucose sucrose and starch.

When concetrated H₂SO₄ in the cold state then no reaction takes place with copper.Anyhow when hot concentrated H₂SO₄ is reacted with Cu metal then SO₂ gas evolves along with the formation of CuSO₄ and H₂O.

The reactions are as follows in which atomic oxygen is evolved:
2KMnO₄+3 H₂SO₄ ……………. K₂SO₄ + 2MnSO₄ + 3H₂O+5[O]
K₂Cr₂O₇+H₂SO₄…………………… K₂SO₄ +Cr₂(SO₄)₃+4H₂O +3[O]

H₂SO₄ is used in almost all the industries.Industrial development of a country can be best estimated from annual consumption of H₂SO₄.It is a barometer of industries.It is employed in:
i) Textile industry          ii) Manufacture of fertilizers
iii)Medicine and chemicals   iv) Process of electroplating.