Formation of Alloys

As the transition elements have similar atomic sizes hence in the crystal lattice, one metal can be readily replaced by another metal giving solid solution and smooth alloys. The alloys so formed are hard and have often high melting point.

Interstitial Compounds

Transition metals form number of interstitial compounds, in which they take up atoms of small size e.g. H, C and N in the vacant spaces in their lattices. The presence of these atoms result in decrease in malleability and ductility of the metals but increases their tensile strength.

Compounds of Iron

Ferrous sulphate (Green vitriol), FeSO4.7H2O

It occurs in nature as copperas and commonly known as hara Kasis.

(a) Preparation

i) By dissolving scrap Fe in dil. H2SO4

ii) From Kipp’s waste which contains ferrous sulphate with some free H2SO4; the latter is neutralised with scrap iron forming FeSO4 and hydrogen.

iii) By the action of air and water on iron pyrites. The solution is treated with scrap iron to remove H2SO4 and to reduce Fe2(SO4)3 to FeSO4.

(b) Properties
i) Hydrated and anhydrous FeSO4 are green and white in colour respectively. It is isomorphous with epsom salt, MgSO4.7H2O and ZnSO4.7H2O. It effervesces on exposure to air.

ii) Light green crystals of FeSO4 lose water and turn brown on exposure to air, due to oxidation.

iii) On heating at 300°C it gives anhydrous FeSO4 which on further heating gives Fe2O3 and SO2.

iv) Like other ferrous salts, it takes up HNO3 forming brown coloured double compound, Fe(NO)SO4, nitroso ferrous sulphate (Ring test for nitrates).

v) It decolourises acidified potassium permanganate and turns acidified dichromate green (reducing character).

vi) It forms double salts with sulphates of alkali metals with general formula R2SO4.FeSO4.6H2O. With ammonium sulphate, it forms a double salt known as ferrous ammonium sulphate or Mohr’s salt, FeSO4.(NH4)2SO4.6H2O. It does not effervesce. It ionises in solution to gives Fe2+, NH4+ and SO42– ions.

Ferric oxide, Fe2O3

(i) It occurs in nature as haematite.

(ii) Fe2O3 is a red powder, insoluble in H2O and not acted upon by air or H2O

(iii) It is amphoteric in nature and reacts with acids and alkalies.

(iv) It is reduced to iron by H2,C and CO.

(v) It is used as a catalyst in the oxidation of CO to CO2 in the Bosch process.

Ferric chloride, FeCl3

(a) Preparation

(i) Hydrated ferric chloride (FeCl3.6H2O) can be prepared by dissolving iron, Fe(OH)3 or ferric oxide in dil. HCl.

(ii) Reaction of Fe with dry Cl2 gives anhydrous FeCl3,

(b) Properties i) Anhydrous salt is yellow, deliquescent compound and highly soluble in H2O. ii) Its aqueous solution is acidic due to hydrolysis. iii) On heating it gives FeCl2 and Cl2. iv) It oxidizes H2S to S, SO2 to H2SO4, SnCl2 to SnCl4 and Na2S2O3 to Na2S4O6.

Copper & Compounds of Copper

(a) These metals are commonly called as coinage or currency metals.
Their general electronic configuration is (n − 1) d10 ns1 .
These show variable valencies +1 , +2 and +3 .

(b) Gradation in properties

(i) The nobility increases from copper to gold.

(ii) The affinity for oxygen also decreases from Cu to Au.

(iii) Copper forms a large number of salts followed by silver followed by gold.

(iv) The ease with which the salts of these elements are reduced increases from Cu to Au.

Compounds of Copper :

(i) Copper sulphate, cupric sulphate or blue vitriol, CuSO4.5H2O.

Preparation

(i) By treating copper scrap or turnings, cuprous oxide, cupric oxide or malachite with H2SO4.

(ii) By roasting copper pyrites, CuFeS2 in air.

Properties

(i) It has 5 molecules of water of crystallisation; all of which can be removed on heating, to form colourless CuSO4 (again coloured with H2O).

(ii) At high temperature it forms cupric oxide.


(iii) It forms double salts with alkali sulphates, e.g. K2SO4.CuSO4.6H2O

(iv) When treated with NH4OH, it first forms precipitate of cupric hydroxide

copper (II) sulphate (Schweitzer’s reagent), used for dissolving cellulose in the manufacture of artificial silk.

(v) It reacts with KCN forming a complex compound K3[Cu(CN)4].

(vi) It liberates iodine from soluble iodides.

Used in the preparation of Bordeaux mixture (CuSO4 solution + lime) which is used to kill moulds and fungi on wines.

Silver & Compounds of Silver

Compounds of Silver :

(A) Silver Nitrate (Lunar caustic) AgNO3

a) Preparation

i) By dissolving Ag in warm dil. HNO3.

b) Properties

i) It is very soluble in H2O and when comes in contact with organic substances (e.g. skin, clothes, etc.) it produces burning sensation and is reduced to metallic silver which is white like the moon Luna hence its name Lunar caustic.

ii) On heating above its melting point it decomposes to silver nitrite.

iii) When treated with soluble halides, it forms the corresponding silver halide.

iv) When treated with alkali, it forms silver oxide which in case of NH4OH dissolves to form complex ion.

v) It reacts with iodine and gives AgIO3 and AgI (when AgNO3 is in excess) or HIO3 and AgI (when I2 is in excess).

vi) With a very dilute solution of Na2S2O3, it gives white precipitate which quickly changes to yellow, brown and finally black due to the formation of silver sulphide. With conc. solution of sodium thiosulphate, it does not give any precipitate.

c) Uses – in volumetric analysis, photography and in silvering of mirrors.

d) Silvering of mirrors – The process is based on the reduction of an ammonical solution of silver nitrate by some reducing agent like glucose, formaldehyde, tartarate, etc.

(B)

Silver Bromide, AgBr :

a) Preparation – by adding AgNO3 solution to soluble bromide solution

b) Properties

i) It is insoluble in water and conc. acid but soluble in excess of strong solution of ammonia (cf. AgCl is soluble in dilute solution of NH4OH, AgI is insoluble in NH4OH solution).

ii) Silver halides are also soluble in KCN and hypo solutions

iii) On heating, it melts to red liquid

iv) It is used as the light sensitive material in photographic films. It is the most sensitive AgX to photo-reduction.

Zinc , Cadmium and Mercury

(a) These are the elements of group 12 having electronic configuration (n − 1) d10 ns2 and +2 oxidation state. In these elements the d-subshell is full, hence these are regarded as non-transition elements which is evident from the following characteristics.

(i) They do not show variable valency except mercury

(ii) Many of their compounds are white.

(iii) Their melting and boiling points are very low.

(b) Unique structure of mercurous ion – Unlike Zn and Cd, Hg exhibits +1 as well as +2 oxidation state. Thus mercurous ion exists as Hg22+ and not as Hg+

(c) Structure of mercurous ion – It consists of two atoms linked by a covalent bond (-Hg – Hg -)2+ and explains the diamagnetic character of mercurous ion.

If it were Hg+ (presence of an unpaired electron in 6s orbital) then mercurous salt should have been paramagnetic.

(d) Anomalous behaviour of mercury,
(i) It is liquid at ordinary temperature while Zn and Cd are solids.

(ii) It is less electropositive than hydrogen and therefore does not displace hydrogen from acids while Zn and Cd does.

(iii) It does not form hydroxide or peroxide, while Zn and Cd do so (iv) Mercuric oxide, on heating, gives metallic mercury and oxygen while oxides of Zn and Cd are stable towards heat.

(v) HgCl2 is covalent while zinc and cadmium chlorides are ionic. With NH3, HgCl2 gives a white ppt. of Hg(NH2)Cl, while Zn and Cd salts form complex ions, [M(NH3)4]2+

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