D Block Elements (Transition), Class 12, Chemistry Detailed Chapter Notes PDF Download

Transition Elements

Definition: They are often called "transition elements" because their position in the periodic table is between s-block and p-block elements

Typically, the transition elements have an incompletely filled d-level. Since Zn group has d¹⁰ configuration and are not considered as transition elements but they are d-block elements.

General Characteristics:

(i) Metallic character : They are all metal and good conductor of heat & electricity

                                                                    CHROMATE - DICHROMATE

Ques. In laboratory K₂Cr₂O₇ is used mainly not Na₂Cr₂O₇. Why?

Sol. Na₂Cr₂O₇ is deliquescent enough and changes its concentration and can not be taken as primary standard solution whereas K₂Cr₂O₇ has no water of crystallisation and not deliquescent.

Ques. How to standardise Na₂S₂O₃ solution in iodometry?

Sol. K₂Cr₂O₇ is primary standard ⇒ strength is known by weighing the salt in chemical balance and dissolving in measured amount of water.Then in acidic solution, add KI

Cr₂O₇^2-  +14 H⁺  + 6I^- → 2Cr³  + 3I₂ + 7H₂O

This I₂ is liberated can be estimated with S₂O₃^2-.

=============================================================== 

Manganate & permanganate

In presence of KClO₃ & KNO₃ the above reaction is more faster because these two on decomposition provides O₂ easily.

Manganate is also obtained when KMnO₄ is boiled with KOH.

4 KMnO₄  + 4KOH  4K₂MnO₄  + 2H₂O + O₂

Props : The above green solution is quite stable in alkali, but in pure water and in presence of acids, depositing MnO₂ and giving a purple solution of permanganate.

3K₂MnO₄ + 2H₂O  2KMnO₄ + MnO₂¯ +  4KOH

                                      purple     dark brown

Prob : = 2.26 V = - 0.56 V

Prove that MnO₄^2- will disproportionate in acidic medium.

Another Method of Prepration:-

 3K₂MnO₄ + 2H₂SO₄ → 2KMnO₄ + MnO₂¯  + 2K₂SO₄ + 2H₂O

or

 3K₂MnO₄ + 2H₂O + 4CO₂ → 2KMnO₄ + MnO₂ + 4KHCO₃

But in the above method  of Mn is lost as MnO₂ but when oxidised either by Cl₂or by O₃

2K₂MnO₄ + Cl₂ → 2KMnO₄ + 2KCl [Unwanted MnO₂ does not form]

OR

2K₂MnO₄ + O₃ + H₂O → 2KMnO₄ + 2KOH + O₂

Oxidising Prop. of KMnO₄ : (in acidic medium)

(i) MnO₄^-  + Fe ² +  H⁺  → Fe ³ + Mn ² + H₂O

(ii) MnO₄^- + I^- + H⁺  → Mn ² + I₂ + H₂O

(iii) MnO₄^- + H₂O₂ + H⁺  → Mn ² + O₂  +H₂O

(iv) MnO₄^-  +SO₂  Mn ² + H₂SO₄

(v) MnO₄^- + NO₂^- + H⁺  → Mn ² + NO₃^-  +H₂O

(vi) MnO₄^- + H₂C₂O₄ + H⁺  → Mn ² + CO₂ + H₂O

(vii) MnO₄^- + H₂S → Mn²   +S¯+H₂O

(1) It is not a primary standard since it is difficult to get it in a high degree of purity and free from trances of MnO₂.

(2) It is slowly reduced to MnO₂ especially in presence of light or acid

4 MnO₄^- + 4 H⁺  → 4 MnO₂ + 2H₂O +3O₂

Hence it should be kept in dark bottles and standardise just before use.

(viii) 2 KMnO₄ + 16 HCl → 2KCl +5 Cl₂ + 8H₂O + 2MnCl₂

Oxidising Prop. of KMnO₄ in alk. medium :

2 MnO₄^-  +2OH^- → 2MnO₄^2- + H₂O +O. 

Then ,

2MnO₄^2- + 2H₂O → 2MnO₂ + 4OH^- + 2O

(i) 2KMnO₄ + H₂O+ KI → 2MnO₂ + 2KOH+ KIO₃

(ii) 2KMnO₄  +3HCO₂K → 2MnO₂  +KHCO₃  +2K₂CO₃ + H₂O

(iii) 2KMnO₄  +3H₂O₂ → 2MnO₂  + 2KOH +2H₂O + 3O₂

Oxidising Prop. in neutral or weakly acidic solution:

(i) 2KMnO₄  +3 MnSO₄  +2H₂O  5 MnO₂ + K₂SO₄ + 2H₂SO₄

or MnO₄^- + Mn ² + 2H₂O → 5MnO₂ + 4H⁺ 

In absence of Zn ² ions, some of the Mn ²⁺ ions may escape, oxidation through the formation of insoluble Mn^II[Mn^IVO₃] manganous permanganite.

(ii) 8 KMnO₄ + 3Na₂S₂O₃  +H₂O → 8 MnO₂ + 3 Na₂SO₄ + 3 S +2 KOH

 Conversion of Mn ² to MnO₄^-

(i) PbO₂ 

(ii) Pb₃O₄ + HNO₃ 

(iii) Pb₂O₃ 

(iv) NaBiO₃/H⁺ 

(v) (NH₄)₂S₂O₈ /H⁺ 

(vi) KIO₄/H⁺ 

Heating effect : 2KMnO₄  K₂MnO₄ + MnO₂ + O₂

^{green Black}

2K₂MNO₄  2K₂MnO₃  +O₂

Silver and its compound

(I)

Preparation : Already done.

Properties :

(i) It is called as lunar caustic because in contact with skin it produces burning sensation like that of caustic soda with the formation of finely divided silver (black colour)

(ii) Thermal decomposition:

(iii) Props. of AgNO₃ : [Already done in basic radical]

6 AgNO₃ + 3I₂ + 3H₂O → 5 AgI +AgIO₃ + 6HNO₃

                                           (excess)

(iv) Ag₂SO₄  2Ag +SO₂  +O₂

(v) A(AgNO₃)  white ppt appears quickly

     B(Na₂S₂O₃)  It takes time to give white ppt.

(vi) Ag₂S₂O₃  +H₂O  Ag₂S +H₂SO₄

AgCl, AgBr, AgI (but not Ag₂S) are soluble in Na₂S₂O₃ forming

[Ag(S₂O₃)₂]^-3 complexes

(vii) AgBr + AgNO₃ →AgBr¯ +KNO₃

^{Pale yellow}

ppt.

Heating effect :

2 AgNO₃  2AgNO₂  O₂

2 AgNO₃  2Ag 2NO O₂

Ag₂O +H₂O₂ → 2Ag +H₂O +O₂

K₂S₂O₈ + 2AgNO₃ + 2H₂O → 2AgO +2KHSO₄ + 2HNO₃

 AgO supposed to be paramagnetic due to d⁹ configuration. But actually it is diamagnetic and exists as

Ag^I[Ag^IIIO₂]

 Reaction involved in developer:

K₂Fe^II(C₂O₄ )₂ + AgBr → KFe^III(C₂O₄)₂ + Ag¯ +KBr

ZinC Compounds

ZnO : It is called as phillospher's wool due to its wooly flock type appearance

Preparation : 1 ] 2Zn O₂ → 2ZnO

2 ] ZnCO₃  ZnO+ CO₂

3 ] 2Zn(NO₃)₂ 2ZnO +4NO₂ + O₂

4 ] Zn(OH)₂  ZnO +H₂O

Purest ZnO : 4ZnSO₄  +4Na₂CO₃₊  3H₂O → ZnCO_{3  +} 3Zn(OH)₂¯ +4Na₂SO₄ + 3CO₂

                                                                         white basic zinc

                                                                          carbonate

Properties : 1 ] ZnO(cold)  ZnO(hot)

white yellow

2 ] It is insoluble in water

3 ] It sublimes at 400ºC

4 ] It is amphoteric oxide

ZnO + 2HCl → ZnCl₂ + H₂O

ZnO +H₂SO₄ → ZnSO₄ + H₂O

ZnO +2NaOH → Na₂ZnO₂ + H₂O

5 ] ZnO → Zn by H₂ & C

ZnO+ H₂  Zn + H₂O

ZnO+ C  Zn +CO

6 ] It forms Rinmann's green with Co(NO₃)₂

2Co(NO₃)₂ → 2CoO 4NO₂  O₂

CoO+ ZnO → CoZnO₂ or CoO - ZnO

Rinmann's green

Uses : (1) As white pigment. It is superior than white lead because it does not turn into black

(2) Rinmann's green is used as green pigment

(3) It is used as zinc ointment in medicine

ZnCl₂

Preparation : ZnO+ 2HCl → ZnCl₂  +H₂O

ZnCO₃  +2HCl → ZnCl₂ + H₂O+ CO₂

Zn(OH)₂  +2HCl → ZnCl₂  +2H₂O

Anh. ZnCl₂ cannot be made by heating ZnCl₂.2H₂O because

ZnCl₂.2H₂O  Zn(OH)Cl +HCl+ H₂O

Zn(OH)Cl  ZnO +HCl

To get anh. ZnCl₂ : Zn Cl₂ → ZnCl₂

Zn 2HCl(dry) → ZnCl₂₊  H₂

or Zn HgCl₂ → ZnCl₂  +Hg

Properties : (i) It is deliquescent white solid (when anhydrous)

(ii) ZnCl₂ + H₂S → ZnS

NaOH → Zn(OH)₂  Na₂[Zn(OH)₄]

NH₄OH → Zn(OH)₂  [Zn(NH₃)₄]² 

Uses : 1] Used for impregnating timber to prevent destruction by insects

2] As dehydrating agent when anhydrous

3] ZnO. ZnCl₂ used in dental filling

ZnSO₄ : -

Preparation : →

Zn +dil. H₂SO₄ → ZnSO₄₊  H₂

ZnO +dil H₂SO₄ → ZnSO₄ + H₂O

ZnCO₃  +dil H₂SO₄ → ZnSO₄ + H₂O CO₂

ZnS +2O₂ → ZnSO₄

ZnS +O₂ → ZnO +SO₂

ZnS +4O₃ → ZnSO₄ + 4O₂

Props. 1] ZnSO₄ . 7H₂O  ZnSO₄ . 6H₂O  ZnSO₄.H₂O ZnSO₄

O₂  +SO₂ + ZnO

Uses : 1] In eye lotion

2] Lithophone making (ZnS BaSO₄) as white pigment.

COPPER compounds

CuO :

Preparation : -

(i) CuCO₃. Cu(OH)₂  2CuO+ H₂O +CO₂ (commercial process)

Malachite Green

(native Cu-carbonate)

(ii) 2Cu+ O₂ → 2CuO    &    Cu₂O +O₂ → 2CuO

(iii) Cu(OH)₂  CuO + H₂O

(iv) 2Cu(NO₃)₂  2CuO +4NO₂ + O₂

Properties :

(i) CuO is insoluble in water

(ii) Readily dissolves in dil. acids

CuO+ H₂SO₄ → CuSO₄ + H₂O

HCl → CuCl₂

HNO₃ → Cu(NO₃)₂

(iii) It decomposes when, heated above 1100ºC

4CuO → 2Cu₂O +O₂

(iv) CuO is reduced to Cu by H₂ or C under hot condition

CuO+ C → Cu +CO­

CuO +H₂ → Cu +H₂O­

CuCl₂ :

Preparation : - CuO+ 2HCl (conc.) → CuCl₂ + H₂O

Cu(OH)₂.CuCO₃  +4HCl → 2CuCl₂  +3H₂O +CO₂

Preparation : -

(i) It is crystallised as CuCl₂. 2H₂O of Emerald green colour

(ii) Dil. solution in water is blue in colour due to formation of

[Cu(H₂O)₄]²  complex.

(iii) Conc. HCl or KCl added to dil. solution of CuCl₂ the colour changes into yellow, owing to the formation of [CuCl₄]^2- .

(iv) The conc. aq. solution is green in colour having the two complex ions in equilibrium 2[Cu(H₂O)₄]Cl₂  [Cu(H₂O)₄]²   +[CuCl₄]^2- + 4H₂O

(v) CuCl₂ → CuCl by no. of reagents

(a) CuCl₂  +Cu-turnings  2CuCl

(b) 2CuCl₂  +H₂SO₃ + H₂O → 2CuCl + 2HCl + 2H₂SO₄

(c) 2CuCl₂ + Zn/HCl → 2CuCl +ZnCl₂

(d) CuCl₂ + SnCl₂ → CuCl +SnCl₄

** CuF₂.2H₂O → light bule

     CuCl₂.2H₂O → green

     CuBr₂ → almost black

     CuI₂ does not exist CuCl₂.2H₂O  CuCl₂  +2H₂O

CuSO₄ :

Preparation : -

CuO + H₂SO₄(dil) → CuSO₄₊  H₂O

Cu(OH)₂  H₂SO₄(dil) → CuSO₄ + 2H₂O

Cu(OH)₂.CuCO₃ + H₂SO₄(dil) → CuSO₄+ 3H₂O +CO₂

 Cu H₂SO₄  +O₂ → CuSO₄ + H₂O [Commercial scale]

^(Scrap)

Cu dil. H₂SO₄ → no reaction {Cu is below H in electrochemical series}

Preparation : -

(i) It is crystallised as CuSO₄.5H₂O

(ii) CuSO₄. 5H₂O  CuSO₄.3H₂O  CuSO₄.H₂O

Blue take places Pale blue Bluish white

CuSO₄(anh.)

white

(iii) Revision with all others reagent

Iron compounds

FeSO₄.7H₂O

Preparation : -

(i) Scrap Fe H₂SO₄ → FeSO₄  +H₂­

(dil.)

(ii) From Kipp's waste

FeS + H₂SO₄ (dil.) → FeSO₄ + H₂S­

(iii) FeS₂ + 2H₂O+  O₂ → FeSO₄ + H₂SO₄

Properties : -

(i) It undergoes aerial oxidation forming basic ferric sulphate

4FeSO₄ + H₂O +O₂ → 4Fe(OH)SO₄

(ii) FeSO₄.7H₂O  FeSO₄  Fe₂O₃  +SO₂ + SO₃

^anh.white

(iii) Aq. solution is acidic due to hydrolysis

FeSO₄ + 2H₂O  Fe(OH)₂  +H₂SO₄

^{weak base}

(iv) It is a reducing agent

(a) Fe²  + MnO₄^-  +H⁺  → Fe³   Mn²   H₂O

(b) Fe²   +Cr₂O₇^2-  +H⁺  → Fe³  Cr³   H₂O

(c) Au³   +Fe²  → Au Fe³ 

(d) Fe²   +HgCl₂ → Hg₂Cl₂¯+ Fe³⁺ 

white ppt.

(v) It forms double salt. Example (NH₄)₂SO₄. FeSO₄.6H₂O

FeO(Black) :

Prepⁿ : FeC₂O₄  FeO +CO +CO₂

Props : - It is stable at high temperature and on cooling slowly disproportionates into

Fe₃O₄ and iron.

4FeO → Fe₃O₄ + Fe

FeCl₂ :

Preparation : - Fe 2HCl  FeCl₂  H₂

OR

2FeCl₃  +H₂  2 FeCl₂  +2HCl

Properties: -

(i) It is deliquescent in air like FeCl₃

(ii) It is soluble in water, alcohol and ether also because it is sufficiently covalent in nature.

(iii) It volatilizes at about 1000ºC and vapour density indicates the presence of Fe₂Cl₄. Above 1300ºC density becomes normal

(iv) It oxidises on heating in air

12FeCl₂  +3O₂ → 2Fe₂O₃ + 8FeCl₃

(v) H₂ evolves on heating in steam

3FeCl₂  +4H₂O → Fe₃O₄  +6HCl +H₂

(vi) It can exist as different hydrated form

FeCl₂.2H₂O → Colourless

FeCl₂.4H₂O → pale green

FeCl₂.6H₂O → green