d-block ELEMENTS 1. INTRODUCTION

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1 d-block ELEMENTS 1. INTRODUCTION The element lying between s- and p-block element of the periodic table are collectively known as transition or transitional elements. (T.E'.S.) Their properties are transitional between the highly electropositive s- block element to least electropositive p-block element. In d- block elements, the last differentiating electron is accommodated to the penultimate shell. The general electronic configuration of transition element is (n-1)d 1-10 ns0, 1 or These elements either in their atomic state or in any of their common oxidation state have partly filled (n-1)d orbitals of (n-1) th main shell. (f) The transition elements have an incompletely filled d-level. Since Zn, Cd, Hg elements have d 10 configuration and are not considered as transition elements but they are d-block elements. ELECTRONIC CONFIGUR ATION I st Transation Series Symbol Sc Ti V C r Mn Fe Co Ni C u Z n Atomic No d electrons s electrons 1 1 Ir regular electronic configurat ion Cr, Cu II nd Transation Series Symbol Y Zr N b M o Tc R u R h P d A g Cd Atomic No d electrons s electrons Irregular electronic configuration Nb, Mo, Ru, Rh, Pd, Ag III rd Transation Series Symbol L a Hf Ta W R e Os Ir P t A u Hg Atomic No d electrons s electrons 1 1 Ir regular electronic configurat ion W, Pt, Au The irregularities in the observed configuration of Cr (3d 5 s 1 instead of 3d s ), Cu (3d 10 s 1 ), Mo (d 5 5s 1 ), Pd ([Kr] d 10 5s 0 ), Au ( [Xe] f 1 5d 10 6s 1 ), Ag ([Kr] d 10 5s 1 ) are explained on the basis of the concept that half-filled and completely filled d-orbitals are relatively more stable than other d-orbitals.. GENERAL PROPERTIES OF d- BLOCK ELEMENTS The properties of d-block elements of any given period are not so much different from one another as those of the same period of non transtion elements.

2 It is due to the fact that, in transition series, there is no change in number of electrons of outermost shell and only change occur in (n-1)d electron from member to member in a period. 3. METALLIC CHAR ACTER All the d-block elements are metals as the numbers of electrons in the outer most shell are one or two. They are hard, malleable and ductile (except Hg). IB group elements Cu, Ag and Au are most ductile and soft. These are good conducter of heat and electricity (due to free e ) Elements of IB group are most conductive in nature. Their order of conductivity is Ag > Cu > Au > Al Covalent and metallic bonding both exist in the atom of transition metals. The presence of partially filled d-subshell favour covalent bonding and metallic bonding. These bonding are favourable also due to possession of one or two electron in outermost energy shell.. REDUCING POWER 5. D ENSIT Y Reducing power of d-block elements depends on their electrode potential. Standard oxidation potential (SOP) of Cu is minimum in the 3d series so it is least reducing elements in 3d series. Au is the least reducing element in the d-block because of highest +ve value of Standard reduction potential. The poor reducing capacity of the transition metal is due to high heats of vaporization, high ionization potential and low heat of hydration of their ions, because reduction potential depends upon all these three factors. The atomic volume of the transition elements are low, compared with s-block, so their density is comparatively high (D = M/V) Os (.57 gm cm 3 ) and Ir (.61 gm cm 3 ) have highest density. In all the groups (except IIIB) there is normal increase in density from 3d to d series, and from d to 5d, it increases just double. Due to lanthanide contraction Ex. Ti < Zr << Hf In 3d series Sc Ti V Cr Mn Fe Co Ni Density increases In 3d series highest density Cu lowest density Sc (f) Some important orders of density Cu Zn Density decreases Fe < Ni < Cu Fe < Cu < Au Fe < Hg < Au 6. MELTING AND BOILING POINTS Melting and boiling point of d-block > s-block Reason : Stronger metallic bond and presence of covalent bond formed by unpaired d-electrons.) In Zn, Cd, and Hg there is no unpaired electron present in d-orbital, hence due to absence of covalent bond melting and boiling point are very low in series. (Volatile metals Zn, Cd, Hg) In 3d series Sc to Cr melting and boiling point increases then Mn to Zn melting and boiling point decreases As the number of d-electron increases, the number of covalent bond between the atoms are expected to increase up to Cr-Mo-W family where each of the d-orbital has only unpaired electrons and the opportunity for covalent sharing is greatest. Mn and Tc have comparatively low melting point, due to weak metallic bond because of stable Half filled (d 5 ) configuration

3 (f) Lowest melting point Hg ( 38 C), Highest melting point W ( ~ 300 C) Melting Point t/ C Sc Ti 1900 V Cr 1710 Mn Fe Co Ni 1083 Cu 0 Zn 0 III B IV B V B VI B VII B VIII I B II B Graphic representation m.p. of 3d-series elements Characteristic properties of transition elements : Variable oxidation state Coloured ions Paramagnetic properties Catalytic properties Formation of alloys (f) Formation of interstitial compounds (g) Formation of complexes. 7. VARIA BLE VALENCY OR VARIA BLE OXIDATION STATES They exhibit variable valency due to involvement of (ns) and (n-1)d electrons. Due to less energy difference between these electrons. The oxidation states of all transiition elements of '3d' series are as follows - Element Conf. Outer electronic configuration Oxidation states Sc 3d 1 s + 3 3d s Ti 3d s V 3d 3 s Cr 3d 5 s Mn 3d 5 s Fe 3d 6 s Co 3d 7 s Ni 3d 8 s Cu 3d 10 s Zn 3d 10 s +

4 Ex. (f) Highest oxidation state of transition elements can be calculated by n + where (n = number of unpaired electrons) It is not applied for Cr and Cu. The transition metal ions having stable configuration like d 0 d 5 or d 10 are more stable. Sc +3, Ti +, V +5, Fe+3, Mn +, Zn + etc. In aqueous medium Cr +3 is stable. Co +3 and Ni + are stable in complexes.. (g) In aqeous medium due to disproportionation Cu +1 is less stable than Cu + while its configuration is 3d 10 (h) Most common oxidation state among the transition elements is +. (i) Highest oxidation state shown by transition elements of 'd' and '5d' series is +8 by Ru () and Os (76). (j) (k) The common oxidation state shown by elements of IIIB i.e., Sc, Y, La and Ac is +3 as their divalent compounds are highly unstable. In lower oxidation state transition elements form ionic compounds and in higher oxidation state their compounds are covalent. (l) They also shows zero oxidation state in their carbonyl compounds like Ni(CO). (m) Ex. Usually transition metal ions in their lower oxidation state act as reducing agents and in higher oxidation state they are oxidising agents. Sc +, Ti +, V +, Fe +, Co + etc are reducing agents Cr +6, Mn +7, Mn +6, Mn +5, Mn + etc are oxidising agents. The relative stability of various oxidation states The relative stabilities of various oxidation states of 3d-series element can be correlated with the extra stability of 3d,3d 5 & 3 d 10 configuration to some extent. Ex. Stability of Ti + (3d 0 ) > Ti 3 + (3d 1 )Mn + (3d 5 ) > Mn 3+ (3d ) The higher oxidation state of d and 5d series element are generally more stable than the elements of 3d series. Ex. (i) vi - Mo O (oxidation state of Mo is +6), stable due to their maximum oxidation state. vi - vi Mo O (d series) & W O, Re vii O (5d series) are more (ii) vi Cr O vii & Mn O (3d-series) are strong oxidizing agents. Strongly reducing states probably do not form fluorides or oxides, but may well form the heavier halides Conversely, strong oxidizing state form oxides & fluoride, but not Bromide and lodide. Ex. (i) V (Vanadium) react with halogens to form VF 5 VCl 5, VBr 3,but doesn' t form VBr 5 or VI 5 because in + 5 oxidation state Vanadium is strong oxidizing agent thus convert Br & I to Br & I respectively, So VBr 3 &VI 3 are formed but not VBr 5 & VI 5. (ii) On the other hand VF 5 is formed because V 5+ ion unable to oxidize highly electronegative & small anion F (iii) Similarly highly electronegative and small O ion formed oxides Ex. VO 3, CrO & MnO etc.

5 Diffrent oxidation state of chloride & oxides compound TiCl TiCl 3 VCl VCl 3 (Ionic, basic) Less ionic (Amphoteric) TiCl VCl VOCl 3 Covalent and Acidic (Strong lewis acid) TiO Ti O 3 TiO VO VO 3 VO 5 CrO3 CrO Cr O 3 MnO Mn O 3 MnO MnO 3 Mn O 7 Ionic, basic Less Ionic (Amphoteric) Acidic, covalent Such compounds are expected to be unstable except in case where vacant d-orbitals are used for accepting lone-pair from -bonding ligand. Ex. [Ni(CO) ], [Ag(CN) ],[Ag)(NH 3 ) ] + 8. COLOUR PROPERTY Most of the transition metal ions exhibit colour property. This is due to d-d transition of unpaired electrons in their t g and e g sets of 'd' orbitals. They require less amount of energy to undergo excitation of electrons. Hence they absorb visible region of light exhibiting colour. Ex. Sc + : [Ar]3d 1, Ti + : [Ar]3d, V + : [Ar]3d 3 Transition metal ions which do not have any unpaired elctrons in their 'd' orbitals like 3d 0 and 3d 10 configurations, do not exhibit any colour property. Ex. (f) Sc +3 : [Ar]3d 0, Cu +1 : [Ar]3d 10, Ti + : [Ar]3d 0 etc are colourless ions. A transition metal ion absorbs a part of visible region of light and emmits rest of the colours, the combination of which, is the colour of emitted light. The colour of metal ion is the colour of the emitted light. In transition metal ion the 'd' orbitals split into lower energy set t g orbitals and higher energy set e g orbitals. The electrons from t g set get excited to higher energy set i.e., e g set. This excitation of electrons is called as 'd-d' transition. Due to this 'd -d' transition the transition metal ions exhibit colour property. Lower energy set = t g Higher energy set = e g Presence of ligands d x - d y z g light d-d Trnsition d-orbitals (degenerate) d xy d yz (t ) g d yz Factors affecting the colour of complex The colour of a transition metal complex depends on- The magnitude of energy difference between the two d-levels ( 0 ),

6 An increase in the magnitude of 0 decreases the wave length ( ) of the light absorbed by the complexes. Thus with a decrease in the 0 (Wavelength of light absorb) 1 the colour of complex changes from Red to Violet. Ex. Complex ions [Co(H O) 6 ] 3+ [Co(NH 3 ) 6 ] 3+ [Co(CN) 6 ] 3 Ligand field strength H O < NH 3 < CN Magnitude of 0 0 (H O) < 0 (NH 3 ) < 0 (CN ) Magnitude of (H O) < (NH 3 ) < (CN ) Colour of the transmitted orange Green-blue violet Colour of absorbed light Green-blue Orange Yellow-green Light (I.e. colour of the complex KMnO (dark pink), K Cr O 7 (orange) having d configuration but they are coloured due to charge trans fer spectrum and charge is transfered from anion to cation. Example of Some coloured metal ions : Ti +3 Purple Cr + 3 Green Mn + Light pink Fe + Green Fe + 3 Yellow Co +3 Pink Ni + Green Cu + Blue Sc 3+ Colourless Ti + Colourless Ti 3+ Purple V + Blue V 3 + Green V + Violet Cr + Blue Cr 3+ Green Mn 3+ Violet Mn + Pink Fe + Green(light) Fe 3+ Yellow Co + Pink Ni + Blue Zn + Colourless 9. MAGNETIC PROPERTIES (f) Generally transition elements exhibits the magnetic property. A paramagnetic substance is one which is attracted into a magnetic field. Paramagnetism is mainly due to the presence of unpaired electrons in atoms or ions or molecules. It varies inversely with temperatures. Diamagnetic substance is one which is slightly repelled by a magnetic field. It's independent of temperature. As is evident most of the transition metal ions have unpaired electrons in their 'd' orbitals. Hence most of the transition metal ions are paramagnetic in nature. Ex.Ti + [Ar]3d, Ti +3 [Ar]3d 1. V + [Ar]3d 3, Cr +3 [Ar]3d 3 Transition metal ions having 3d 0 and 3d 10 configuration exhibit diamagnetic nature. The total magnetic moment of a substance is the resultant of the magnetic moments of all the individual electrons. The magnetic moment () created due to spinning of unpaired electrons can be calculated by using n(n ) Where - 'n' is the number of unpaired electrons in the metal ion. = Magnetic moment in Bohr Magnetons (B.M.) (g) (h) The magnetic moment of diamagnetic substances will be zero. Transition metal ions having d 5 configuration will have maximum number of unpaired electrons therefore they will be maximum paramagnetic in nature.

7 1 0. CATALYTIC PROPERTY Transition elements and their compounds exhibit catalytic properties. This is due to their variable valency as well as due to the free valencies on their surface. When transition elements and their compounds are in powdered state, their catalytic properties exhibited will be to a greater extent. This is due to greater surface area available in the powdered state. Transition metals and their compounds exhibiting catalytic properties in various processes are- C a t a l y s t U s e d TiCl 3 Used as the Ziegler-Natta catalyst in the production of polythene. V O 5 Convert SO to SO 3 in the contact process for making H SO MnO Used as a catalyst to decompose KClO 3 to give O Fe Promoted iron is used in the Haber-Bosch process for making NH 3 FeCl 3 Used in the production of CCl from CS and Cl FeSO and H O PdCl Used as Fenton's reagent for oxidizing alcohols to aldehydes. Wacker process for converting C H + H O + PdCl to CH 3 CHO + HCl + Pd. Pd Pt/PtO Used for hydrogenation (e.g. phenol to cyclohexanone). Adams catalyst, used for reductions. Pt Formerly used for SO SO 3 in in the contace process for making H SO Pt/Rh Cu Cu/V CuCl Ni Formerly used in the ostwald process for making HNO 3 to oxidize NH 3 to NO Is used in the direct process for manufacture of (CH 3 ) SiCl used to make silicones. Oxidation of cyclohexanol/cyclohexanone mixture to adipic acid which is used to make nylone-66 Decon process of making Cl from HCl Raney nickel, numerous reduction processes (e.g. manufacture of hexamethylenediamine, productiomn of H from NH 3, reducing anthraquinone to anthraquinol in the production of H O 1 1. FORM ATION OF ALLOY Transition elements have maximum tendency to form alloys. The reactivity of transition elements is very less and their sizes are almost similar. Due to this a transition metal atom in the lattice can be easily replaced by other transition metal atom and hence they have maximum tendency to form alloys. In the alloys, ratio of component metals is fixed. These are extremly hard and have high melting point.

8 SOME IMPORTANT ALLOY Bronze Cu (75-90 %) +Sn ( 10-5 %) Brass Cu ( %) +Zn (0-0 %) Gun metal (Cu + Zn + Sn) (87 : 3 : 10) German Silver Cu + Zn + Ni ( : 1 : 1) Bell metal Cu (80 %) + Sn (0 %) (f) Nichrome (Ni + Cr + Fe) (g) Alnico (Al, Ni, Co) (h) Type Metal Pb + Sn + Sb (i) Alloys of steel Vanadium steel V ( %) Chromium steel Cr ( - %) Nickel steel Ni (3-5 %) Manganese steel Mn (10-18 %) Stainless steel Cr (1-1 %) & Ni ( - %) Tunguston steel W (10-0 %) Invar Ni (36 %) (j) 1 Carat Gold 5 % Au + Ag (1 to 30 %) + Cu (1-8 %) (k) Carat Gold 100 % Au (l) Solder Pb + Sn (m) Magnellium Mg (10%) + Al (90%) (n) Duralumin (Al + Mn + Cu) (o) Artificial Gold Cu (90 %) + Al (10%) (p) Constantan Cu(60%) + Ni (0%) % of Carbon in different type of Iron N a m e % of C Wrought Iron 0.1 to 0.5 Steel 0.5 to.0 Cast Iron.6 to.3 Pig Iron.3 to.6 1. FORM ATION OF INTERSTITIAL COMPOUNDS Transition elements form interstitial compounds with smaller sized non metal elements like hydrogen, carbon, boron, nitrogen etc. The smaller sized atoms get entrapped in between the interstitial spaces of the metal lattices. These interstitial compounds are nonstoichiometric in nature and hence cannot be given any definite formula. The smaller sized elements are held in interstitial spaces of transition elements by weak Vander Waals forces of attractions. The interstitial compounds have essentially the same chemical properties as the parent metals but they differ in physical properties such as density and hardness. The process of adsorption of excess of H atom by the transition metals like Pd, Pt etc is called occlusion.

9 1 3. NONSTOICHIOMETRY The transition elements sometimes form nonstoichiometric compounds due to variable valency. These are the compounds of indefinite structure & proportion. For example, lron (II) Oxide FeO should be written as a bar over the formula FeO to indicate the ratio of Fe & O atom is not exactly 1:1 (Fe 0. 9 O & Fe 0.8 O), VSe (VSe 0.98 VSe 1. ), Non stoichiometry is shown particularly among transition metal compounds of the group 16 elements (O,S,Se,Te). Some times nonstoichiometry is caused by defect in the solid structure. 1. POTASSIUM DICHROMATE (K Cr O 7 ) Prepar ation It is prepared from Chromite ore or Ferrochrome or Chrome iron. (FeO.Cr O 3 or FeCr O ). The various steps involved are. Preparation of sodium chromate (Na CrO ) : The powdered chromite ore in fused with sodium hydroxide or sodium carbonate in the presence of air in a reverberatory furnace. FeCr O + 16NaOH + 7O 8Na CrO + Fe O 3 + 8H O or FeCr O + 8Na CO 3 + 7O 8Na CrO + Fe O 3 + 8CO After the reaction the roasted mass is extracted with water. So sodium chromate is completely dissolved while ferric oxide is left behind. Formation of sodium dichromate (Na Cr O 7 ) from sodium chromate (Na CrO ) : The solution of sodium chromate is filtered and acidified with dil./con. H SO acid giving its dichromate. Na CrO + H SO Na Cr O 7 + Na SO + H O On cooling, sodium sulphate being less soluble crystallizes out as Na SO.10H O and is removed. The resulting solution contains sodium dichromate (Na Cr O 7 ). Formation of potassium dichromate from sodium dichromate : Properties The hot concentrate solution of sodium dichromate is heated with calculated amount of KCl. Na Cr O 7 + KCl K Cr O 7 + NaCl Sodium chloride, being the least soluble precipitates out from the hot solution and is removed by filtration. Orange red crystals of potassium dichromate separate out from mother liquid on cooling. Colour and Melting Point :- Orange red crystals. 670 K Solubility :- Moderately soluble is cold water but readily soluble in hot water. Action of Heat :- It decompose on heating to give potassium chromate, chromic oxide and oxygen. K Cr O 7 Heat K CrO + Cr O 3 + 3O Potassium Chromic chromate oxide

10 Action of Alkalies :- On heating with alkalies the orange colour of dichromate solution changes to yellow due to the formation of chromate ions. K Cr O 7 + KOH K CrO + H O 7 or Cr O OH CrO H O This chromate on acidifying reconverts into dichromate. K CrO + H SO K Cr O 7 + K SO + H O 7 or CrO H Cr O H O The interconversion is explained by the fact that dichromate ion and chromate ion exist in equilibrium at a ph of about. 7 Cr O H O CrO H When alkali added, H + consumed so forward direction. When acid added, H + increases so backward direction. Chromyl chloride Test :- When potassium dichromate is heated with conc. H SO acid and a soluble metal chloride (ex. NaCl) orange red vapours of chromyl chloride (CrO Cl ) are formed. K Cr O 7 + NaCl + 6H SO KHSO + NaHSO + CrO Cl + 3H O (f) Reaction with H O :- Acidified solution of dichromate ions give deep blue colour solution with H O due to the formation of [CrO(O ) ] or CrO 5. The blue colour fades away gradually due to the decomposition of CrO 5 into Cr +3 ions and oxygen. O O O Cr O H O H CrO H O Cr (Butterfly stucture) O O (g) Action with HCl :- Potassium dichromate reacts with hydrochloric acid and evolves chlorine. K Cr O 7 + 1HCl KCl + CrCl 3 + 7H O + 3Cl (h) Action of con. H SO (i) In cold, red crystals of chromic anhydride are formed. (ii) K Cr O 7 + H SO CrO 3 + KHSO + H O On heating the mixture oxygen is evolved. (i) K Cr O 7 + 8H SO K SO + Cr (SO ) 3 + 8H O + 3O Oxidising properties The dichromates act as powerful oxidising agent in acidic medium. In presence of dil H SO, K Cr O 7 liberates Nascent oxygen and therefore acts as an oxidising agent. K Cr O 7 + H SO K SO + Cr (SO ) 3 + H O + 3[O] In terms of electronic concept the Cr O 7 ion takes up electrons in the acidic medium and hence acts as an oxidising agent. 3 7 Cr O 1H 6e Cr 7H O (i) It oxidises iodides to iodine :- Cr O 7 + 1H + + 6e Cr H O [I I + e ] 3 Cr O 7 + 1H + + 6I Cr I + 7H O or K Cr O 7 + 7H SO + 6KI K SO + Cr (SO ) 3 + 7H O + 3I

11 (ii) Acidified ferrous sulphate to ferric sulphate Cr O 7 + 1H + + 6e Cr H O Fe + Fe 3+ + e ] 6 Cr O 7 + 1H + + 6Fe + Cr Fe H O or K Cr O 7 + 6FeSO + 7H SO Cr (SO ) 3 + 3Fe (SO ) 3 + 7H O + K SO (iii) Oxidises H S to sulphur Cr O 7 + 1H + + 6e Cr H O H S S + H + + e ] 3 Cr O 7 + 3H S + 8H + Cr S + 7H O or K Cr O 7 + 3H S + H SO Cr (SO ) 3 + 3S + 7H O + K SO U s e s Similarly, it oxidises sulphites to sulphates, chlorides to chlorine, nitrites to nitrates, thiosulphates to sulphates and sulphur and stannous (Sn + ) salts to stannic (Sn + ) salts SO Cr O 8H 3SO Cr H O NO Cr O 8H 3NO Cr H O S O Cr O 8H 3SO 3S Cr H O 3 7 6Cl Cr O 1H 3Cl Cr 7H O 3 7 3Sn Cr O 1H 3Sn Cr 7H O It oxidises SO to sulphuric acid. K Cr O 7 + H SO K SO + Cr (SO ) 3 + H O + 3O SO + O + H O H SO For volumetric estimation of ferrous salts, iodides and sulphites. For preparation of other chromium compounds such as chrome alum (K SO, Cr (SO ) 3.H O), chrome yellow (PbCrO ) and chrome red (PbCrO.PbO). Used in photography for hardening of gelatin film. It is used in leather industry (chrome tanning) Chromic acid mixture is used for cleaning glassware, consist of K Cr O 7 and Con. H SO. (f) (g) S tr uc t ur e In organic chemistry, it is used as an oxidising agent. In dyeing and calico printing. The chromate ion has tetrahedral structure in which four atoms around chromium atom are oriented in a tetrahedral arrangement.

12 The structure of dichromate ion consist of two tetrahedra sharing an oxygen atom at the common corner POTASSIUM PERMANGANATE (KMnO ) Prepar ation Potassium permanganate is prepared from mineral pyrolusite (MnO ). The preparation involves the following steps. Conversion of pyrolusite ore to potassium manganate The pyrolusite MnO is fused with caustic potash (KOH) or potassium carbonate in the presence of air or oxidising agents, such as KNO 3 or KClO 3 to give a green mass due to the formation of potassium manganate (K MnO ). MnO + KOH + O K MnO + H O MnO + K CO 3 + O K MnO + CO Oxidation of potassium manganate to potassium permanganate The green mass is extracted with water resulting is green solution of potassium manganate. The solution is then treated with a current of Cl or ozone or CO to oxidise K MnO to KMnO. The solution is concentrated and dark purple crystals of KMnO seperate out. K MnO + Cl KCl + KMnO K MnO + O 3 + H O KMnO + KOH + O 3K MnO + CO K CO 3 + MnO + KMnO Alternatively, alkaline potassium manganate is electrolytically oxidised. Electrolytic method :- The potassium manganate solution is taken in an electrolytic cell which contains iron cathode and nickel anode. When current is passed the manganate ion in oxidised to permanganate ion at anode and hydrogen is liberated at cathode. K MnO K + + MnO At anode : MnO MnO + e Green Purple At cathode : H + + e H H H

13 Properties Colour and M.P. :- Dark violet crystalline solid, M.P. 53 K Solubility :- Moderately soluble is room temperature, but fairly soluble in hot water giving purple solution. Heating :- When heated strongly it decomposes at 76 K to give K MnO and O. KMnO 76 K K MnO + MnO + O Solid KMnO gives KOH, MnO and water vapours, when heated in current of hydrogen. KMnO + 5H KOH + MnO + H O Action of alkali :- On heating with alkali, potassium permanganate changes into potassium manganate and oxygen gas is evolved. KMnO + KOH K MnO + H O + O Action of con. H SO :- With cold H SO, it gives Mn O 7 which on heating decomposes into MnO. KMnO + H SO Mn O 7 + KHSO + H O Mn O 7 MnO + 3O (f) Oxidising character :- KMnO acts as powerful oxidising agent in neutral, alkaline or acidic solution because it liberates nascent oxygen as :- Acidic solution :- Mn + ions are formed KMnO + 3H SO K SO + MnSO + 3H O + 5[O] or MnO + 8H + + 5e Mn + + H O equal wt. Neutral solution :- MnO is formed M 5 KMnO + H O KOH + MnO + 3[O] or MnO + H O + 3e MnO + OH M equal wt. 3 During the reaction the alkali produced generates the alkaline medium even if we start from neutral medium. Alkaline medium :- Manganate ions are formed. KMnO + KOH K MnO + H O + [O] Reactions in Acidic Medium : In acidic medium KMnO oxidizes Ferrous salts to feric salts MnO + 8H + + 5e Mn + + H O Fe + Fe +3 + e ] 5 MnO + 5Fe + + 8H + Mn + + 5Fe +3 + H O Oxalates to CO : MnO + 8H + + 5e Mn + + H O] C O CO + e ] 5 MnO + 5C O + 16H + Mn CO + 8H O

14 Iodides to Iodine MnO + 8H + + 5e Mn + + H O] I I + e ] 5 10I + MnO + 16H + Mn + + 5I + 8H O Sulphites to sulphates MnO + 8H + + 5e Mn + + H O] SO 3 + H O SO + H + + e ] 5 5SO 3 + MnO + 6H + Mn + + 5SO + 3H O It oxidizes H S to S MnO + 8H + + 5e Mn + + H O] S S + e ] 5 MnO + 16H + + 5S Mn + + 5S + 8H O (f) It oxidizes SO to sulphuric acid KMnO + 3H SO K SO + MnSO + 3H O + 5[O] SO + H O + [O] H SO ] 5 KMnO + 5SO + H O K SO + MnSO + H SO (g) It oxidizes Nitrites to nitrates KMnO + 3H SO K SO + MnSO + 3H O + 5[O] KNO + O KNO 3 ] 5 KMnO + 5KNO + 3H SO K SO + MnSO + 5KNO 3 + 3H O Reactions in Neutral Medium : It oxidizes H S to sulphur : KMnO + H O KOH + MnO + 3 [O] H S + O H O + S] 3 KMnO + 3H S KOH + MnO + H O + 3S It oxidizes Manganese sulphate (MnSO to MnO ) manganese dioxide : KMnO + H O KOH + MnO + 3 [O] MnSO + H O + O MnO + H SO ] 3 KOH + H SO K SO + H O KMnO + 3MnSO + H O 5MnO + K SO + H SO

15 It oxidizes Sodium thiosulphate to sulphate and sulphur : KMnO + H O KOH + MnO + 3 [O] Na S O 3 + O Na SO + S] 3 KMnO + 3Na S O 3 + H O MnO + 3Na SO + KOH + 3S Reactions in alkaline Medium It oxidizes Iodides to Iodates in alkaline medium : KMnO + H O KOH + MnO + 3 [O] KI +3O KIO 3 KMnO + KI + H O MnO + KOH + KIO 3 Alkaline KMnO (Baeyers reagent) oxidizes ethylene to ethylene glycol. CH CH + H O + [O] CH OH CH OH S tr uc t ur e MnO U s e s Used in volumetric analysis for estimation of ferrous salts, oxalates, and other reducing. agents. It is not used as primary standard because it is difficult to obtain it in the pure state. It is used as strong oxidising agent in the laboratory as well as industry. As disinfectant and germicide. In dry cells. A very dilute solution of KMnO is used for washing wounds COMPOUNDS OF IRON FERROUS SULPHATE (GREEN VITRIOL), FeSO 7H O : This is the best known ferrous salt. It occurs in nature as copper and is formed by the oxidation of pyrites under the action of water and atmospheric air. FeS + 7O + H O FeSO + H SO It is commonly known as harakasis.

16 Prepar ation It is obtained by dissolving scrap iron in dilute sulphuric acid. Fe + H SO FeSO + H The solution is crystallised by the addition of alcohol as ferrous sulphate is sparingly soluble in it. Properties Action of heat : At 300 C, it becomes anhydrous. The anhydrous ferrous sulphate is colourless. The anhydrous salt when strongly heated, breaks up to form ferric oxide with the evolution of SO and SO 3. FeSO 7H O Green 300 C FeSO 7HO White High temperature Fe O 3 + SO + SO 3 The aqueous solution of ferrous sulphate is slightly acidic due to its hydrolysis. FeSO + H O Fe(OH) + H SO Weak base It reduces gold chloride to gold. Strong acid AuCl 3 + 3FeSO Au + Fe (SO ) 3 + FeCl 3 It reduces mercuric chloride to mercurous chloride. [HgCl Hg Cl + Cl] 3 [3FeSO + 3Cl Fe (SO ) 3 + FeCl 3 ] 6HgCl + 6FeSO 3Hg Cl + Fe(SO ) 3 + FeCl 3 A cold solution of ferrous sulphate absorbs nitric oxide forming dark brown addition compound, nitroso ferrous sulphate. FeSO + NO FeSO NO Nitroso ferrous sulphate (Brown) The NO gas is evolved when the solution is heated. U s e s Ferrous sulphate is used for making blue black ink. It is used as a mordant in dyeing. It is also used as an insecticide in agriculture. It is employed as a laboratory reagent and in the preparation of Mohr's salt. Ferrous- oxide FeO ( Black) Preparation : FeC O In absence of air FeO + CO + CO Properties : It is stable at high temperature and on cooling slowly disproportionates into Fe 3 O and iron Ferrous chloride (FeCl ) heated in Preparation : Fe + HCl a current of HCl FeCl + H Properties : FeCl 3 + H FeCl + HCl It is deliquescent in air like FeCl 3 It is soluble in water, alcohol and ether also because it is sufficiently covalent in nature

17 It volatilises at about 1000 C and vapour density indicates the presence of Fe Cl. Above 1300 C density becomes normal It oxidises on heating in air 1FeCl + 3O Fe O 3 + 8FeCl 3 H evolves on heating in steam 3FeCl + H O Fe 3 O + 6HCl + H (f) It can exist as different hydrated form FeCl H O colourless FeCl H O pale green FeCl 6H O green 1 7. COMPOUND OF ZINC Zinc oxide ( ZnO) zinc white Prepar ation ZnO is formed when ZnS is oxidised ZnS + 3O ZnO + SO Zn(OH) on strongly heating gives ZnO Zn(OH) ZnO + H O Zinc on burning in air gives ZnO (commercial method) Zn + O ZnO Properties ZnO is white when it is cold, a property that has given it a use as a pigment in paints. However, it changes colour, when hot, to a pale yellow. This is due to change in the structure of lattice. ZnO is soluble both in acid and alkali and is thus amphoteric in nature. ZnO + H + Zn + + H O ZnO + OH + H O [Zn(OH) ] or zincate ion ZnO + HCl ZnCl + H O ZnO + NaOH Na ZnO + H O sodium zincate ZnO ZnO + C >1000 C Zn + CO ZnO + CO Zn + CO It is preferred to white lead as it is not blackened by H S. It is also used in medicine and in the perparation of Rinman's green (ZnCo O ) Zinc Sulphate (ZnSO ) Prepar ation ZnSO 7H O (also called white vitriol) is formed by decomposing ZnCO 3 with dil. H SO ZnCO 3 + H SO ZnSO + H O + CO

18 By heating ZnS (zinc blende) in air at lower temperature and dissolving the product in dil. H SO ZnS + 3.5O ZnO + ZnSO + SO Properties ZnO + H SO ZnSO + H O Highly soluble in water and solution is acidic in nature due to hydrolysis ZnSO + H O Zn(OH) + H SO ZnSO 7H O 100 C ZnSO 6H O 80 C ZnSO T > 760 C ZnO + SO 3 It slowly effloresces when exposed to air. It is isomorphous with Epsom salt and used in the manufacture of lithophone (which is a mixture of BaS + ZnSO and is used as white pigment). Zinc chloride (ZnCl ) Prepar ation ZnO + HCl ZnCl + H O ZnCO 3 + HCl ZnCl + H O + CO It crystallises as ZnCl HO Zn(OH) + HCl ZnCl + H O Anhydrous ZnCl cannot be made by heating ZnCl H O because ZnCl H O Zn(OH)Cl + HCl + H O Zn(OH)Cl ZnO + HCl To get anhydrous ZnCl Zn + Cl ZnCl Properties Zn + HCl(dry) ZnCl + H Zn + HgCl ZnCl + Hg It is deliquescent white solid (when anhydrous) ZnCl + H S ZnS ZnCl + NaOH Zn(OH) ZnCl + NH OH Zn(OH) excess excess Na [Zn(OH) ] [Zn(NH 3 ) ] + U s e s Used for impregnating timber to prevent destruction by insects As dehydrating agent when anhydrous ZnO ZnCl used in dental filling

19 1 8. COMPOUND OF SILVER Silver Nitrate (Lunar Caustic) AgNO 3 Prepar ation When Ag is heated with dil HNO 3, AgNO 3 is formed. Crystals separate out on cooling the concentrated solution of AgNO 3 3Ag + HNO 3 3 AgNO 3 + NO + H O Colourless crystalline compound soluble in H O and alcohol ; m.p. 1 C When exposed to light, it decomposes hence, stored in a brown coloured bottle: Ag + NO + O Properties, red hot, T > AgNO 1 C 3 AgNO + O It is reduced to metallic Ag by more electropositive metals like Cu, Zn, Mg and also by PH 3. AgNO 3 + Cu Cu(NO 3 ) + Ag 6AgNO 3 + PH 3 + 3H O 6Ag + 6HNO 3 + H 3 PO 3 It dissolves in excess of KCN: AgNO KCN 3 AgCN KCN K[Ag(CN) ] white ppt soluble potassium argentocyanide AgNO 3 gives white precipitate with Na S O 3 ; white precipitate changes to black. AgNO 3 + Na S O 3 Ag S O 3 + NaNO 3 white ppt Ag S O 3 + H O Ag S + H SO black Ammoniacal AgNO 3 is called Tollen's reagent and is used to identify reducing sugars (including aldehydes): RCHO + Ag + + 3OH RCOO + Ag + H O It is called 'silver mirror test' of aldehydes and reducing sugar (like glucose, fructose). Some important reaction of AgNO 3 Ag HNO 3 O + Ag + NO Ag S O 3 Ag S black white H O Na S O 3 RCHO,OH AgNO 3 KCN Ag K[Ag(CN) ],T>1 C PH 3 Cu Ag + Cu + Ag Ag + H PO + HNO 3 3 3

20 1 9. COMPOUND OF COPPER Cupric oxide ( CuO) It is called black oxide of copper and is found in nature as tenorite. Prepar ation By heating Cu O in air or by heating copper for a long time in air (the temperature should not exceed above 1100 C) Cu O + 1 O CuO Cu + O CuO By heating cupric hydroxide, Cu(OH) CuO + H O By heating copper nitrate, Cu(NO 3 ) CuO + NO + O On a commercial scale, it is obtained by heating molachite which is found in nature. CuCO 3 Cu(OH) CuO + CO + H O Properties It is black powder and stable to moderate heating. The oxide is insoluble in water but dissolves in acids forming corresponding salts. CuO + HCl CuCl + H O CuO + H SO CuSO + H O CuO + HNO 3 Cu(NO 3 ) + H O When heated to C, it is converted into cuprous oxide with evolution of oxygen. CuO Cu O + O It is reduced to metallic copper by reducing agents like hydrogen, carbon and carbon monoxide. CuO + H Cu + H O CuO + C Cu + CO CuO + CO Cu + CO U s e s It is used to impart green to blue colour to glazes and glass. Cupric Chloride, (CuCl H O) Prepar ation Cu + HCl + O CuCl + H O CuO + HCl CuCl + H O Cu(OH) CuCO 3 + HCl CuCl + 3H O + CO Cu + Cl CuCl CuCl H O 150 C HCl gas CuCl + H O

21 Properties The aqueous solution is acidic due to its hydrolysis. CuCl + H O Cu(OH) + HCl The anhydrous salt on heating forms Cu Cl and Cl CuCl Cu Cl + Cl It is readily reduced to Cu Cl by copper turnings or SO gas, or hydrogen (Nascent obtained by the action of HCl on Zn) or SnCl. CuCl + Cu Cu Cl CuCl + SO + H O Cu Cl + HCl + H SO CuCl + H Cu Cl + HCl CuCl + SnCl Cu Cl + SnCl A pale blue precipitate of basic cupric chloride, CuCl 3Cu(OH) is obtained when NaOH is added. CuCl + NaOH Cu(OH) + NaCl CuCl + 3Cu(OH) CuCl 3Cu(OH) It dissolves in ammonium hydroxide forming a deep blue solution. On evaporating of this solution deep blue crystals of tetrammine cupric chloride are obtained. CuCl + NH OH Cu(NH 3 ) Cl H O + 3H O U s e s It is used as a catalyst in Deacon's proces. It is also used in medicines and as an oxygen carrier in the preparation of organic dyestuffs. Copper Sulphate (Blue Vitriol), CuSO 5H O Copper sulphate is the most common compound of copper. It is called as blue vitriol or nila thotha. Prepar ation CuO + H SO CuSO + H O Cu(OH) + H SO CuSO + H O Cu(OH) CuCO 3 + H SO CuSO + 3H O + CO On commercial scale : it is prepared from scrap copper. The scrap copper is placed in a perforated lead bucket which the dipped into hot dilute sulphuric acid. Air is blown through the acid. Copper sulphate is crystallised from the solution. Cu + H SO + 1 O (air) CuSO + H O Properties It is a blue crystalline compound and is fairly soluble in water. Heating effect CuSO 5H O Exposure CuSO 3H O 100 C CuSO H O 30 C CuSO Blue Pale blue Bluish white White CuSO 70 C CuO + SO3 SO + 1 O

22 Action of NH OH : With ammonia solution, it forms the soluble blue complex. First it forms a precipitate of Cu(OH) which dissolves in excess of ammonia solution CuSO + NH OH Cu(OH) + (NH )SO Cu(OH) + NH OH + (NH ) SO Cu(NH 3 ) SO + H O Tetrammine cupric sulphate The complex is known as Schwitzer's reagent which is used for dissolving cellulose in the manufacture of artificial silk. Action of alkalies : Alkalies form a pale bule precipitate of copper hydroxide. CuSO + NaOH Cu(OH) + Na SO Action of potassium iodide : First cupric iodide is formed which decomposes to give white cuprous iodide and iodine. [CuSO + KI CuI + K SO ] CuI Cu I + I CuSO + KI Cu I + K SO + I (f) Action of H S : When H S is pased through copper sulphate solution, a black precipitate of copper sulphide is formed. CuSO + H S CuS + H SO The black precipitate dissolves in conc. HNO 3 3CuS + 8HNO 3 3Cu(NO 3 ) + NO + 3S + H O (g) Action of potassium sulphocyanide : Cupric sulphocyanide is formed. CuSO + KCNS Cu(CNS) + K SO If SO is passed through the solution, a white precipitate of cuprous sulphocyanide is formed. CuSO + KCNS + SO + H O Cu (CNS) + K SO + H SO [This is the general method for obtaining curprous compounds.] (h) Action of sodium thiosulphate etc. CuSO + Na S O 3 CuS O 3 + Na SO CuS O 3 + Na S O 3 Cu S O 3 + Na S O 6 3Cu S O 3 + Na S O 3 Na [Cu 6 (S O 3 ) 5 ] Sodium cuprothiosulphate U s e s Copper sulphate is used for the preparation of other copper compounds. It is used in agriculture as a fungicide and germicide. It is extensively used in electric batteries.