Halides of phosphorus preparation and properties, Group 15 P Block Elements

Halides of phosphorus preparation and properties, Group 15 P Block Elements

Halides of Phosphorus :

Phosphorus forms two types of halides :

  • Phosphorus trihalide.
  • Phosphorus pentahalide.

Phosphorus reacts with chlorine and forms two types of chlorides, which are discussed below:

Phosphorus Trichloride (PCl3)

Preparation :

→ It can be prepared when dry chlorine gas is passed over heated white phosphorus. The vapours of PCI, formed which are then distilled over and condensed in a receiver by cold water.

P4 + 6Cl2 → 4PCl3

→ It can also be prepared by the reaction of thionyl chloride with white phosphorus.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 1

Structure :

→ Phosphorus atom in phosphorus trichloride is sp3-hybridised. Its shape is pyramidal. In PCl3, three sp3-hybrid orbitals show overlapping with porbitals of chlorine atom. Thus, three P – Cl sigma bonds are formed with P – Cl bond length 204 pm. The fourth sp3-hybrid orbital contains one lone pair of electrons. Therefore, its shape is pyramidal. In PCl3 the Cl – P – Cl bond angle is 100.4°.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 2

→ Properties : Its physical and chemical properties are as follows:

→ Physical Properties

  • It is colourless oily liquid.
  • Its specific gravity is 1.6.
  • Its boiling point is 347 K while melting point is 161 K.
  • It has a pungent smell.

Chemical Properties : Its chemical properties are as follows:

It reacts with water and fumes in moist air. The fumes are due to the formation of HCl. With HCl it also forms phosphorus acid.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 3

Reaction with oxygen : PCl3 slowly reacts with dry oxygen and phosphorus oxychloride is formed.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 4

Reaction with chlorine : When PCl3 reacts with chlorine, phosphorus pentachloride is formed.

PCl3 + Cl2 → PCl5

Reaction with sulphur : When PCl3 reacts with sulphur, thiophosphorus oxychloride is formed.
PCl3 + S → PSCl3

Halides of phosphorus preparation and properties, Group 15 P Block Elements

Reaction with sulphur mono chloride : When PCl3 reacts with sulphur mono chloride, PCl3 is formed.
PCl3 + S2Cl2 → PCl5 + 2PSCl3

Reaction with sulphur trioxide : When PCl3 reacts with SO3, phosphorus oxychloride is formed.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 5

PCl3 acts as a reducing agent : PCl3 behaves as reducing agent and reduces various compounds.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 6

Reaction with Grignard reagent : PCl3 reacts with Grignard Reagents and form substituted phosphine.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 7

Reaction with organic compounds : It reacts with those organic compounds which has-OH
group as shown below:

With alcohols, it forms alkyl chloride.

3C2H5OH + PCl3 → 3C2H5Cl + H3PO3

With carboxylic acid, it forms acetyl chloride.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 8

With benzenesulphonic acid, it forms benzene sulphonyl chloride.

3C6H5SO2OH + PCl3 → 3C6H5 SO2Cl + H3PO3

Reaction with finely divided metals : On heating with finely divided metals it reacts to form metal chlorides.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 9

Reaction with sulphuric acid : It reacts with sulphuric acid and converts it into chloro sulphonic acid.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 10

Uses :

It is used as reducing agent.
It is used to replace hydroxyl group (-OH) by chlorine atom (-Cl) in organic compound.

Phosphorus Pentachloride (PCl5)

Preparation :

It can be prepared by the reaction of white phosphorus with excess of chlorine.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 11

When PCl3 reacts with chlorine then PCl5 is formed.

PCl3 + Cl2 → PCl5

When phosphorus reacts with SO2Cl2 then phosphorus pentachloride is formed.
P4 + 10SO2Cl2 → 4PCl5 + 10SO2

Halides of phosphorus preparation and properties, Group 15 P Block Elements

Structure Phosphorus atom in PCl5 is sp3 hybridised. Its shape is triangular bipyramidal.

→ In PCl5 there are two types of bond i.c., equatorial P – Cl bonds and axial P – Cl bonds. Axial bonds are longer than equatorial bonds due to the fact that the axial bond pairs suffer more repulsion as compared to equatorial bond pairs. The bond length are as follows:

Halides of phosphorus preparation and properties, Group 15 P Block Elements 12

Properties Its physical and chemical properties are as follows:

Physical Properties :

  • It is a yellowish white powder.
  • It has pungent smell.
  • Its sublimation temperature is 433 K and melting point is 318 K on heating under pressure.
  • It fumes in moist air due to the formation of HCl.
  • It has strong affinity for water.

Chemical Properties : Its chemical properties are as follows:

Stability : PCl5 is less stable. It easily decomposes into PCl3 and Cl2.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 13

Reaction with water PCl5 has great affinity for water. It fumes in moist air due to the formation of HCl. The related reactions are as follows:

Halides of phosphorus preparation and properties, Group 15 P Block Elements 14

Reaction with metals : Phosphorus pentachloride reacts with finely divided metals forming chlorides.

2Ag + PCl5 → 2AgCl + PCl3
Sn + 2PCl5 → SnCl4 + 2PCl3

Reaction with phosphorus pentasulphide : It reacts with phosphorus pentasulphide, and phosphorus thiochloride is formed.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 15

Reduction of PCl5 : PCl5 can be reduced by hydrogen into PCl3.

PCl5 + 2H → PCl3 + 2HCl

Reaction with sulphur dioxide : When phosphorus pentachloride reacts with SO2 then POCl3 and SOCl2 are formed.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 16

Reaction with phosphorus pentoxide : When PCl5 reacts with P2O5, POCl3 is formed.

6PCl5 + P4O10 → 10POCl3

Reaction with chloride ion aceptors : Phosphorus pentachloride forms addition products with chloride ion aceptor such as BCl3, AlCl3 etc.

PCl5 + BCl3 → [PCl4]+ [BCl4]

Halides of phosphorus preparation and properties, Group 15 P Block Elements

Reaction with potassium fluoride : PCl5 reacts with KF then K+[PF6] complex is formed.

Halides of phosphorus preparation and properties, Group 15 P Block Elements 17

Reaction with organic compounds : PCl5 is used to replace -OH group from any organic compound with-Cl.

With carboxylic acid

Halides of phosphorus preparation and properties, Group 15 P Block Elements 18

With ethyl alcohol

Halides of phosphorus preparation and properties, Group 15 P Block Elements 19

Uses It is used as a reagent to replace -OH group from organic compound with -Cl.

Chemistry Notes

Phosphine preparation and properties, Group 15 P Block Elements

Phosphine preparation and properties, Group 15 P Block Elements

Phosphine (PH3) :

It was discovered by Gengembre in 1783. It is analogous to ammonia. It is known as hydrogen phosphide.

Preparation of Phosphine

It can be prepared as follows:

→ From Phosphides : When metallic phosphide reacts with water and mineral acids then phosphine is formed.

Phosphine preparation and properties, Group 15 P Block Elements 1

→ From Phosphorous Acid : When phosphorus acid is heated at 478-483 K temperature then pure phosphine is prepared.

Phosphine preparation and properties, Group 15 P Block Elements 2

The above reaction is disproportionation reaction.

→ Laboratory Preparation : In laboratory phsophine can be prepared by heating white phosphorus with concentrated NaOH solution is an inert atmosphere of carbon dioxide or coal gas.

Phosphine preparation and properties, Group 15 P Block Elements 3

→ In above reaction phosphorus dihydride is also prepared with phosphine which is highly inflammable.

Phosphine preparation and properties, Group 15 P Block Elements 4

→ Thus, as soon as, these gas bubbles when comes in contact with air, catches fire spontaneously forming rings of smoke known as vortex rings.

Phosphine preparation and properties, Group 15 P Block Elements

→ It is interesting to note that pure phosphine itself is non-inflammable. Actually the combustion is due to the presence of highly inflammable P, H, which burns and forms vortex ring.

Phosphine preparation and properties, Group 15 P Block Elements 5
Phosphine preparation and properties, Group 15 P Block Elements 6

→ From Phosphonium lodide : When phosphonium iodide is heated with sodium hydroxide solution, then phosphine is prepared.

Phosphine preparation and properties, Group 15 P Block Elements 7

Structure of Phosphine

→ The structure of phosphine is pyramidal. Phosphorus atom in phosphine is sp hybridised. In PH,,three bonds are formed by the overlaping of sp -hybrid orbitals with 18-orbital of hydrogen, one lone pair of electrons is also present. The H-P-H bond angle is 936 and P-H bond length is 142 pm

Phosphine preparation and properties, Group 15 P Block Elements 8

Properties of Phosphine

Physical and chemical properties of phosphine are as follows:

Physical Properties : Some important physical properties are :

  • It is a colourless gas with rotten fish or garlic smell.
  • It is heavier than air.
  • It is highly poisonous gas.
  • It is slightly soluble in water.
  • Its solution in water is neutral to litmus paper.
  • It liquifies at 185.5 K and solidifies at 139.5 K.

Chemical Properties : Some important chemical properties of phosphine are as follows :

→ Decomposition : In presence of sunlight or on heating upto 713 K, it decomposes into red phosphorus and hydrogen.

Phosphine preparation and properties, Group 15 P Block Elements 9

→ Basic Nature : Phosphine is neutral to litmus but it behaves as weak base. It is weaker base than ammonia. It reacts with halogen acids and form phosphonium salts.

Phosphine preparation and properties, Group 15 P Block Elements 10

→ Combustibility : Phosphine when heated to 423 K in air or oxygen phosphorus pentaoxide is formed.

2PH3 + 4O2 → P2O5 + 3H2O

→ Phosphorus pentaoxide when reacts with water forms meta phosphoric acid.

P2O5 + H2O → 2HPO3

Phosphine preparation and properties, Group 15 P Block Elements

→ Reaction with Metallic Salts : Phosphine when reacts with metallic salts of copper, silver and mercury etc., then it forms phosphide.

Phosphine preparation and properties, Group 15 P Block Elements 11

→ Formation of addition compounds : Phosphine forms addition compounds with anhydrous AlCl3 and SnCl4.

AlCl3 + 2PH3 → AlCl3 . 2PH3
SnCl4 + 2PH3 → SnCl4 . 2PH3

→ It also forms addition compounds with cuprous chloride solution in HCl.

Phosphine preparation and properties, Group 15 P Block Elements 12

→ Reaction with N3O : The mixture of PH, and N O or PH, and NO explodes in presence of electric spark.

Phosphine preparation and properties, Group 15 P Block Elements 13

→ Reaction with Nitric Acid : Phosphine when comes in contact with nitric acid then it begins to burn.

Phosphine preparation and properties, Group 15 P Block Elements 14

→ Reaction with Chlorine : Phosphine reacts with chlorine and it forms phosphorus pentachloride.

Phosphine preparation and properties, Group 15 P Block Elements 15

Uses of Phosphine

  • The spontaneous combustion of phosphine is technically used in Holme’s signals.
  • To produce these signals the containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea.
  • When the gases evolved, they burn and serve as a signal. It is also used in smoke screens.
  • It is used for making metallic phosphide.

Chemistry Notes

Phosphorus preparation and properties, Group 15 P Block Elements

Phosphorus preparation and properties, Group 15 P Block Elements

Phosphorus :

→ Phosphorus was first discovered by Brand in 1669. Scheele isolate it from bone ash. In 1777 Lavoisier proved that it is an element. It glow in dark (greekword, phos-light and phero-carry) so it is named as phosphorus.

Phosphorus preparation and properties, Group 15 P Block Elements

→ Phosphorus is the second element of nitrogen family. Its atomic number is 15. Its electronic configuration is 12 2s2 2p6 3s2 3p3. It is a very reactive non-metal hence it does not exist in free state. Some important minerals of phosphorus are as follows :

Phosphorus preparation and properties, Group 15 P Block Elements 1

→ Phosphorus is found in our teeth, bones, muscles, brain and nerve tissues. It is also present in milk, fish, beans, eggs etc.

Preparation :

→ When phosphorite ie, Ca3(PO4)2 is heated with coke and silica in an electric furnace upto 1770 K, then phosphorus is isolated.

Phosphorus preparation and properties, Group 15 P Block Elements 2

→ The vapours obtained from above process are condensed then white phosphorus is isolated.

Allotropic form of Phosphorus :

Phosphorus show the property of allotropy. The main allotropes of phosphorus are as follows:

→ White or Yellow Phosphorus : It is the common allotrope of phosphorus. It is obtained by heating phosphorite rock with coke and sand in an electric are at 1770 K temperature.

Phosphorus preparation and properties, Group 15 P Block Elements 3

→ On exposure to air, it becomes yellow, therefore it is called yellow phosphorus. It exist as P, molecules. In P molecule, each phosphorus atom is linked to three other P-atoms by covalent bonds. Each phosphorus atom in PA molecule have one lone pair of electrons. The P-P-P bond angle in P, molecule is 60°.

Phosphorus preparation and properties, Group 15 P Block Elements 4

Some important characteristics of white phosphorus are as follows:

  • It is transparent, white and soft waxy solid.
  • It can be cut easily with knife.
  • It has a garlic odour.
  • It is insoluble in water but soluble in organic solvents like CS, alcohol, benzene etc.
  • It’s vapours are highly poisonous. The persons working in phosphorus industry, develop a disease known as Phossy jaw. In this diesase jaw bones of persons decay slowly.
  • Ita melting point is 317 K while its boiling point is 553 K because of presence of very weak Vander Waal’s force of attraction.
    In contact with air, it undergoes slow combustion and glow in dark. This phenomenon is known as phosphorescence. Hence phosphorus shows phosphorescence.
  • In pure state it is white in colour but on standing it converts slowly into yellow colour.
  • Its ignition temperature is very low so it readily catches fire or show combustion with air and produce dense white fumes.
    P4 + 5O2 → P4O10
  • Due to above reason white phosphorus is stored under water.
  • Upon heating with aqueous NaOH in inert atmosphere it evolves phosphine gas.

Phosphorus preparation and properties, Group 15 P Block Elements 5

→ Red Phosphorus : Red phosphorus can be obtained by heating white or yellow phosphorus in an inert atmosphere of CO, at 573 K for several days.

Phosphorus preparation and properties, Group 15 P Block Elements 6

→ Red phosphorus has polymeric structure in which P, tetrahedral units are linked together as shown in Fig. 7.11

Phosphorus preparation and properties, Group 15 P Block Elements 7
Some important characteristic of red phosphorus are as follows:

  • It is dark red coloured solid.
  • It is brittle and odourless.
  • It is non-poisonous in nature.
  • It is insoluble in water as well as in carbon disulphide.
  • It is denser than white phosphorus. Its specific gravity is 2.1.
  • It does not show phosphorescence.
  • It is quite stable and have quite high (543 K) ignition temperature. Thus, it does not catch fire easily.
  • It is not chemically active hence it burns on heating above 533 K temperature.
    Phosphorus preparation and properties, Group 15 P Block Elements 6
  • It does not react with caustic soda so with the help of this property it can easily be separated with white phosphorus.

→ Black Phosphorus : Black phosphorus can be prepared by heating white phosphorus at 473 K temperature under very high pressure in an inert atmosphere.

Phosphorus preparation and properties, Group 15 P Block Elements 9

→ It has double layered structure having crystalline lattice. In black phosphorus each atom is forming three strong bonds with its neighbours. Here the bond angle is 99. It is highly polymeric. Its structure is shown in Fig. 7.12

Phosphorus preparation and properties, Group 15 P Block Elements 10

→ Some important characteristics of black phosphorus are as follows:

  • It is found in two allotropic form:
    • α-Black phosphorus
    • β-Black phosphorus
  • It has black metallic lustre.
  • Its melting point is 860 K.
  • Its specific gravity is 2.69.
  • It is chemically inert and it does not oxidise in air.
  • It does not ignite in air upto 673 K temperature.
  • It is a moderate conductor of heat and electricity.

→ Thus, we can say that in three allotropic forms of phosphorus, white phosphorus is very reactive while black phosphorus is the least reactive. All the properties of three allotropic forms of phosphorus has been summarised in table 7.8. Table

Phosphorus preparation and properties, Group 15 P Block Elements

7.8 : Differences between white, red and black phosphorus

Properties White Red phosphorus Black phosphorus
Physical state phosphorus Soft waxy solid Brittle powder Crystalline
Colour White but turns yellow on exposure to air Dark red Black
Odour Garlic smell Odourless
Specific gravity 1.8 2.1 2.69
Ignition temperature 307 K 543 K 673 K
Melting point 317 K Sublimes in absence of air at 543. 860 K
Stability Less stable More stable Most stable
Chemical Very Less Least
reactivity reactive reactive reactive
Reaction with NaOH Evolve phosphine No reaction
Physiological action Poisonous Non-poisonous

Phosphorus preparation and properties, Group 15 P Block Elements

Uses of Phosphorus :

  • Red phosphorus is generally used in match box industry.
  • White phosphorus is used in making rat poison.
  • It is used in making smoke screen.
  • Phosphorus is used in making Bronze alloy, Bronze is an alloy of Cu, Sn and P.
  • It is also used in making fire works.
  • Radioactive P-32 is used in the treatment of lukemia (blood cancer) and other blood related diseases.

Chemistry Notes

Nitric acid preparation and properties, Group 15 P Block Elements

Nitric acid preparation and properties, Group 15 P Block Elements

Nitric Acid :

→ Nitrogen forms three main oxoacids. These are

  • Hyponitrous acid – H2N2O2
  • Nitrous acid – HNO2
  • Nitric acid – HNO3

→ Among all oxoacids of nitrogen, nitric acid, (HNO3) is the most important acid of nitrogen. Nitric acid, (HNO3) is stable and a strong acid. It acts as a strong oxidising agent. Alchemists named it aqua fortis (meaning strong water), Glauber prepared it first time by the action of sulphuric acid and nitre.

Nitric acid preparation and properties, Group 15 P Block Elements

Preparation :

Nitric acid can be prepared by various methods, some of them are as follows:

→ Laboratory Method: In the laboratory, nitric acid is prepared by heating sodium or potassium nitrate (KNO3 or NaNO3) with concentrated sulphuric acid in a glass retort to about 423-475 K.

Nitric acid preparation and properties, Group 15 P Block Elements 1

→ Commercial production of nitric acid by Ostwald’s Process : On commerical scale, nitric acid is prepared by the catalytic oxidation of ammonia. This process is known as Ostwald’s Process. The catalytic oxidation of ammonia is done by atmospheric oxygen at about 500 K and 9 × 105 Pa (9 bar). In presence of Pt or Rh gauge as catalyst.

Nitric acid preparation and properties, Group 15 P Block Elements 2

→ The nitric oxide thus formed is recycled and the aqueous HNO3 is concentrated by distillation to give 68% HNO3 by mass. Further concentration of 98% can be achieved by dehydrating it by concentrated H2SO4.

→ Nitric acid prepared from Oswald’s method is very dilute. It can be concentrated to about 69% by distilling it under reduced pressure. It can be further concentrated by dehydration. It is dehydrated by concentrated H2SO4 upto 98%.

→ The acid obtained by dehydration process contains dissolved NO2. So it is brown in colour. This NO2 gas is thus removed by passing bubbling air through it.

Structure of nitric acid

In gaesous state, HNO3 exist as a planar molecule. Its structure is as follows

Nitric acid preparation and properties, Group 15 P Block Elements 3

Resonating structure of nitric acid is as follows

Nitric acid preparation and properties, Group 15 P Block Elements 4

Nitrate ion formed after the removal of Hion from nitric acid also show the resonating structure as follows

Nitric acid preparation and properties, Group 15 P Block Elements 5

Physical Properties of Nitric Acid

  • Anhydrous nitric acid is a colourless liquid which has pungent smell.
  • Impure nitric acid is yellow in colour due to the presence of dissolved oxides of nitrogen.
  • It boils at 355.6 and freezes at 231.4 K.
  • It is soluble in water in all proportions but 68% nitric acid by mass forms an azeotropic or constant boling mixture with water.
  • Its specific gravity is 1.504
  • It show corrosive action on the skin and causes painful sores.

Nitric acid preparation and properties, Group 15 P Block Elements

Chemical Properties of Nitric Acid

The chemical properties of nitric acid are as follows:

Acidic nature : It is a strong monobasic acid which forms only one type of salt. It ionises completely in water.

HNO3(aq) + H2O(l) → H3O+ (aq) + NO3(aq)

It forms salts with bases like metallic oxides, metallic hydroxides, metallic carbonates and bicarbonates etc.

Nitric acid preparation and properties, Group 15 P Block Elements 6

Decomposition : On heating, nitric acid decomposes into nitrogen dioxide, oxygen and water.

Nitric acid preparation and properties, Group 15 P Block Elements 7

Oxidising Nature : Nitric acid acts as a strong oxidising agent because it readily gives nascent oxygen.

Nitric acid preparation and properties, Group 15 P Block Elements 8

Some important oxidising reactions of nitric acid are as follows:

Oxidation of non-metals : The nascent oxygen coming from nitric acid oxidises various non-metals as follows

Nitric acid preparation and properties, Group 15 P Block Elements 9

Oxidation of metalloids : Semi-metals or metalloids such as arsenic and antimony are also oxidised by conc. HNO3. Involved reactions are as follows

Nitric acid preparation and properties, Group 15 P Block Elements 10

Oxidation of compounds : Both concentrated and dilute nitric acid can oxidise the various compounds.

Oxidation of sulphur dioxide into sulphuric acid

Nitric acid preparation and properties, Group 15 P Block Elements 11

Oxidation of hydrogen sulphide into sulphur

Nitric acid preparation and properties, Group 15 P Block Elements 12

Oxidation of ferrous sulphate Into fernc sulphate in acidic medium

Nitric acid preparation and properties, Group 15 P Block Elements 13

Oxidation of hydrogen iodide into iodine

Nitric acid preparation and properties, Group 15 P Block Elements 14

Similarly HBr also oxidises into Br2

Oxidation of Klinto l2 Both dilute and conc. acid can oxidise.

Nitric acid preparation and properties, Group 15 P Block Elements 15

Oxidation of stannous chloride into stannic chloride in presence of HCI

7SnCl2 + 14HCl + 3HNO3 → 7SnSl4 + NH2OH + NH4NO3 + 5H2O

→ Oxidation of metals: With an exception of gold and platinum (known as noble metals), nitric acid can attack all the metals forming a variety of products. The action of nitric acid on metals can be explained as follows.

Nitric acid preparation and properties, Group 15 P Block Elements

→ Action on metals that are more electropositive than hydrogen : Metals like Mg, Al, Mn, Zn, Fe, Pb etc. are lying above hydrogen in electrochemical series. These metals are highly electropositive in nature. When these metals react with nitric acid having different concentration then a variety of compounds are formed. Some reactions are given below

Reaction with zinc (Zn): Zinc forms different products with very dilute, dilute and concentrated acids as follows:

Nitric acid preparation and properties, Group 15 P Block Elements 16

Reaction with Iron : Similar to zinc, iron also reacts with varying concentration of nitric acid and different products are formed.

Nitric acid preparation and properties, Group 15 P Block Elements 17

Nitric acid preparation and properties, Group 15 P Block Elements 18

→ Action on metals that are less electropositive than hydrogen : Metals like Cu, Ag, Hg etc. are lying below in electrochemical series. They form different products with varying concentration of nitric acid. Some of them are as follows:

Reaction with copper

Nitric acid preparation and properties, Group 15 P Block Elements 19

Reaction with silver : Silver (Ag) reacts similarly as copper.

Nitric acid preparation and properties, Group 15 P Block Elements 20

Reaction with Mercury

Nitric acid preparation and properties, Group 15 P Block Elements 21

→ Action on Noble metals Nitric acid as such have no effect on noble metals like gold, platinum, irridium etc. But these metals can dissolve in aqua-regia (3 parts conc. HCl and one part conc. HNO3). Actually aqua-regia release nascent chlorine which reacts with noble metals as follows.

Nitric acid preparation and properties, Group 15 P Block Elements 22

→ Action on metals which become passive : Some metals like Fe, CO, Ni, Cr, Al become passive towards concentrate nitric acid. It is due to the formation of a thin layer of metal oxide over the surface of metal. This layer of oxide protects the surface of metal.

→ It prevents further action of nitric acid on the surface. Thus, we can say that the inertness exhibited by the metals due to the formation of metal oxide layer is known as passivity.

→ Xanthoproteic Test : Nitric acid attacks on protein and forms a yellow coloured nitro compound. This yellow coloured nitro compound is known as xanthoprotein. This, test is knwon as xanthoprotic test and it is used to detect protein.

Nitric acid preparation and properties, Group 15 P Block Elements

→ Brown Ring Test : Brown ring test is used to detect NO3 ion in a mixture. In this test first of all an aqueous solution of salt is taken in test-tube. To this aqueous solution now freshly prepared ferrous sulphate solution is added.

→ Now concentrated sulphuric acid is added to this solution drop by drop along the side walls of test tube without disturbing the solution, a dark brown colour ring is obtained at the interface of two layers i.e. oily layer of sulphuric acid and aqueous layer.

The reactions are as follow

Nitric acid preparation and properties, Group 15 P Block Elements 23

Nitric acid Uses

The main uses of nitric acid are as follows

  • In manutacturing of various explosive like T.N.T., Picric acid, Dynamite etc.
  • In preparation of various nitro compound like ammonium nitrate, basic calcium nitrate etc.
  • In manufacturing of artificials silk, dyes, drugs, perfumes etc.
  • As a laboratory reagent
  • In the puritication of gold and platinum as aqua regia and for pickling (cleaning) of stainless steel
  • In manufacturing of some important compounds used in perfumes, dyes and medicines.
  • As a solvent for metals, for etching designs on brass and bronze wares.
  • In manufacturing of silver nitrate, sodium nitrate and potassium nitrate etc.
  • As oxidiser in rocket fuels.

Chemistry Notes