Chemistry Notes for NEET Chapter 21 PDF

60 Chapter E3 21 Chemical Analysis Analytical chemistry deals with qualitative and quantitative analysis of substances. (vi) Tests for NH : It is a colourless gas with a characteristic ammonical smell. It gives white fumes of NH 4 Cl with HCl , Qualitative analysis : A salt consists of two parts kno...

60 Chapter E3 21 Chemical Analysis Analytical chemistry deals with qualitative and quantitative analysis of substances. (vi) Tests for NH : It is a colourless gas with a characteristic ammonical smell. It gives white fumes of NH 4 Cl with HCl , Qualitative analysis : A salt consists of two parts known as radicals. The positively charged part of a salt (cation) which has been derived from a base is termed as basic radical and the negatively charged part of salt (anion) which has been derived from an acid is termed as acidic radical. In qualitative inorganic analysis, the given compound is analysed for the basic and acid radicals (i.e., the cations and the anions), that it contains. For NH 3  HCl NH 4 Cl. With Nessler’s reagents, it gives brown ppt. ID 3 White fumes    NH 3 U 2 K 2 HgI4 Nessler ' s reagent D YG example zinc blende is analysed for the Zn 2  and S 2  ions that it contains. Test for Different Gases (1) Colourless gases (i) Tests for CO : It is colourless and odourless gas. It gives white ppt. with lime water which dissolves on passing excess of CO 2. 2 Ca(OH ) 2  CO 2 CaCO 3   H 2 O White ppt. U Lime water CaCO 3  CO 2  H 2 O Ca(HCO 3 ) 2 White ppt. Excess It  KOH NH 2 HgOHgI  7 KI  2 H 2 O Iodine of Millon' s base ( Brown ppt) gives deep blue colour with Cu SO 4 solution, CuSO 4  4 NH 3 Cu (NH 3 )4 SO 4. NH 3 dissolves in water to Deep blue give NH 4 OH , which being NH 3  H 2 O NH 4 OH ⇌ basic, NH 4 turns red litmus blue,   OH. (vii) Tests for HCl gas : It is colourless gas with a pungent irritating smell. It turns moist blue litmus paper red i.e., it is acidic in nature. It gives white ppt. with AgNO 3 solution. This white ppt. is soluble in NH 4 OH. HCl  AgNO 3 AgCl  HNO 3 ; White ppt. AgCl  2 NH 4 OH Ag(NH 3 ) 2   2 H 2 O. Soluble (viii) Test for CH 3 COOH vapours : These vapours are colourless with a vinegar like smell. So lub le ST (ii) Test for CO : It is colourless and odourless gas. It burns with a blue flame. 2CO  O 2 2CO 2 (2) Coloured gases (i) Tests for Cl : It is a greenish yellow gas with a pungent smell. In small quantity it appears almost colourless. It bleaches a moist litmus paper, Cl 2  H 2 O 2 HCl  O ; Colour  O Colourless. Blue litmus 2 (iii) Test for O : It is colourless and odourless gas. It rekindles a glowing splinter. 2 (iv) Tests for H S : It is a colourless gas with a smell of rotten eggs. It turns moist lead acetate paper black. 2 (CH 3 COO) 2 Pb  H 2 S 2CH 3 COOH  PbS Black (v) Tests for SO : It is a colourless gas with a suffocating odour of burning sulphur. It turns acidified K 2 Cr2 O7 solution green. paper first turns red and then becomes colourless. (ii) Tests for Br : Brown vapours with a pungent smell. It turns moist starch paper yellow. 2 (iii) Tests for I : Violet vapours with a pungent smell. It turns moist starch paper blue. 2 2 3 SO 2  K 2 Cr2 O7  H 2 SO 4 K 2 SO 4  Cr2 (SO 4 )3  H 2 O Green (iv) Tests for NO : Brown coloured pungent smelling gas. It turns moist starch KI paper blue 2 2 KI  2 NO 2 2 KNO 2  I 2 ; I 2  Starch Blue colour. It turns ferrous sulphate solution black, Observation 3 FeSO 4  NO 2  H 2 SO 4 Fe 2 (SO 4 )3  FeSO 4. NO  H 2 O Result (a) A gas or vapour is evolved. Blackbrown Vapour, evolved, test with litmus paper. Systematic Procedure for Qualitative Analysis of Inorganic Salts It involves the following steps : (1) Preliminary tests (2) Wet tests for acid radicals and (3) Wet tests for basic radicals. (1) Preliminary tests Table : 21.1 Colour Dark-brown or reddish fumes (oxides of nitrogen), acidic in reaction. Salt Oxides : MnO2 , FeO, CuO, Co 3 O4 , Ni2 O3 Sulphides : Dinitrogen oxide CO 2 is Ag2 S , CuS , Cu 2 S , FeS, CoS , NiS , PbS, HgS , Bi2 S 3 (blackish brown) Hydrated CuSO 4 , anhydrous CoSO 4 Orange KO 2 , evolved, dichromate NH 3 is evolved which turns red SO 2 is evolved, salts, (K 2 Cr2 O7 ), Sb 2 S 3 , ferrous salts, potassium permanganate (KMnO4 ) , some copper (II) salts Dark brown K 2 Cr2 O7 turns hydrogen Ammonium salts. PbO2 , Ag2 O, CdO, Fe2 O3 , CuCrO4 , FeCl3 Sulphates and thiosulphates. green, is evolved, turns lead acetate paper black, or cadmium acetate yellow. Cl 2 is evolved, yellowish green SnS D YG Brownish yellow or decolourises fuschin colour. H 2S hydrated which U Nickel Carbonates carbonates. litmus blue. ferricyanides Green water becomes turbid. acidified some lime ID Blue E3 Colour 60 Oxygen is evolved (i) Physical examination : It involves the study of colour, smell, density etc. Black The vapour is alkaline. The vapour is acidic. Compounds with water of crystallisation Ammonium salts, acid salts, and hydroxides. (usually accompanied by change of colour) Ammonium salts. Readily decomposable salts of strong acids. Nitrates,chlorates and certain oxides. Ammonium nitrate or nitrate mixed with an ammonium salt. Nitrates and nitrites of heavy metals. gas, bleaches litmus paper, turns KI – starch blue, poisonous. Br2 is evolved (reddish brown, (but yellow in aq. solution) turns fluorescent paper red). Hydrates, sulphides or sulphides in the presence of water. Unstable chlorides e.g., copper chlorides in the presence of oxidising agents. Bromides in the presence of oxidising agents. MnCO 3 I2 Light pink Hydrated manganese salts Ammonium and mercury salts. Reddish pink Hydrated cobalt (II) salts condensing to black crystals (b) A sublimate is formed White sublimate Red HgI2 , Pb3 O4 Grey sublimate Hg Steel grey, garlic odour As Yellow sublimate S , As2 S 3 HgI2 (Re d ) Yellow U Pale brown CdS , PbI2 , AgBr, AgI , chromates ST (ii) Dry heating : Substance is heated in a dry test tube. (Re d ) 2 Hg  O2 (Silvery deposit )  CuCO 3  CuO  CO 2 As2 O3 , Sb 2 O3 Table : 21.3  2 Pb3 O 4  6 PbO O 2 (Re d ) (Yellow )  ZnO 3  ZnO  CO 2 (White) (Green ) Free iodine and certain iodides Action of heat on different compounds : Many inorganic salts decomposes on heating, liberating characteristic gases. A few such reactions are tabulated as follows, Table : 21.2  2 HgO  is evolved, violet vapours Yellow (hot )  2 PbO2  2 PbO O 2 ( Brown )  CuSO 4.5 H 2 O  CuSO 4  5 H 2 O ( Blue) (White) White (cold )  CuSO 4  CuO  SO 3  2 FeSO 4  Fe2 O 3  SO 2  SO 3 2 Ag 2 O 4 Ag  O 2  2 Zn( NO 3 )2  2 ZnO  4 NO 2  O 2 450 C 2 AgNO3    2 Ag  2 NO 2  O 2 2Cu(NO 3 )2 2CuO  4 NO 2  O 2 (White) ( Brown ) 2 Ag 2 CO 3 4 Ag  2CO 2  O2 2 Pb(NO 3 )2 2 PbO  4 NO 2  O2 (NH 4 )2 Cr2 O7 N 2  Cr2 O 3  4 H 2 O 2 NaHCO 3 Na 2 CO 3  CO 2  H 2 O NH 4 HCO 3 NH 3  CO 2  H 2 O CaCO 3 CaO  CO 2 2 NaNO 3 2 NaNO 2  O2 MgCO3 MgO  CO 2 Red hot 2 NH 3    N 2  3 H 2 2 Mg(NO 3 )2 2 MgO  4 NO 2  O 2 2Ca(NO 3 )2 2CaO  4 NO 2  O2 Red hot Al2 (SO 4 )3   Al2 O 3  3 SO 3 2CaSO 4.2 H 2 O 2CaSO 4.H 2 O  2 H 2 O 2 AlCl3.6 H 2 O Al2 O 3  6 HCl  9 H 2 O  2 BeSO 4  2 BeO  2SO 2  O 2 350 C   2 AgNO2  O 2 2 AgNO3   2 MgSO4  2 MgO  2SO 2  O 2  2 ZnSO 4  2 ZnO  2SO 2  O 2  (COO)2 Sn  SnO  CO 2  CO CaC 2 O4 CaCO 3  CO NH 4 NO 2 N 2  2 H 2 O NH 4 NO 3 N 2 O  2 H 2 O 2 KClO3 2 KCl  3O2 2 FeCl3 2 FeCl 2  Cl 2 Li2 CO 3 Li2 O  CO 2 (COO)2 Fe FeO  CO  CO 2 2 KMnO4 K 2 MnO4  MnO2  O 2 MgCl2. 6 H 2 O HgCl2  Hg NH 4 Cl NH 3  HCl (Orange) Hg(NO 3 )2 Hg  2 NO 2  O2 E3 o 60 (Plaster of Paris) (Green) 1 2 LiNO 3 Li 2 O  2 NO 2  O 2  2Co (NO 3 )2  2CoO  4 NO 2  O 2 ID  2CuCl 2  Cu 2 Cl 2  Cl 2 2 4 K 2 Cr2 O7 4 K 2 CrO4 + 2Cr2 O3  3O2  2 Mg(NH 4 )PO4  Mg2 P2 O7  H 2 O  2 NH 3  2 Zn(NH 4 )PO4  Zn 2 P2 O7  H 2 O  2 NH 3  2(ZnCl 2.H 2 O)  Zn 2 OCl 2  2 HCl  H 2 O U  ZnCl 2. 2 H 2 O  Zn(OH )Cl  HCl  H 2 O  K 4 Fe(CN )6  4 KCN  Fe  2C  N 2  2[FeCl3.6 H 2 O]  Fe2 O3  9 H 2 O  6 HCl o 800 C   2 ZnO  2SO 2  O 2 2 ZnSO 4  D YG   Na 2 B4 O7.10 H 2 O  Na 2 B4 O7  2 NaBO2  B2 O3 (Glassy bead) o o Red hot 100 C 160 C   HBO2    H 2 B4 O7  H 3 BO3    B 2 O 3 o o o 450 C 70 C 100 C ZnSO 4.7 H 2 O   ZnSO 4.6 H 2 O    ZnSO 4.H 2 O    ZnSO 4  H 2O (iii) Flame test 5 H 2 O ST U Characteristic flame colour : Certain metals and their salts impart specific colours to Bunsen burner flame. (a) Pb imparts pale greenish colour to the flame. (b) Cu and Cu salts impart blue or green colour to the flame. (c) Borates also impart green colour to the flame. (d) Ba and its salts impart apple green colour to the flame. (e) Sr imparts crimson red colour to the flame. (f) Ca imparts brick red colour to the flame. (g) Na imparts yellow colour to the flame. (h) K imparts pink-violet (Lilac) colour to the flame. (i) Li imparts crimson-red, Rb imparts violet and Cs imparts violet colours to the flame. (j) Livid- blue flame is given by As, Sb and Bi. (iv) Borax bead test : The transparent glassy bead (NaBO2  B2 O3 ) when heated with inorganic salt and the colour produced gives some idea of cation present in it. Table : 21.4 Colour of bead in oxidising flame Greenish when hot, blue in cold. Dark green in hot and cold Deep – blue Yellow when hot Violet in hot and cold Brown in cold Colour of bead in reducing flame Red and opaque Basic radical present Cu Same Cr Deep blue Green Colourless Grey or black or opaque Co Fe Mn Ni Microcosmic salt bead test : Microcosmic salt, Na(NH 4 )HPO4.4 H 2 O is also used to identify certain cations just like borax. When microcosmic salt is heated in a loop of platinum wire, a colourless transparent bead of sodium metaphosphate is formed. Na (NH 4 )HPO4.4 H 2 O Na(NH 4 )HPO4  4 H 2 O Na(NH 4 )HPO4 NaPO3  NH 3  H 2 O Now NaPO3 orthophosphates. reacts with metallic oxides to give coloured NaPO3  CuO NaCuPO4 (Blue); NaPO3  CoO NaCoPO4 (Blue); NaPO3  Cr2O3 NaPO3.Cr2O3 (Green) Sustance Decrepitates (v) Charcoal cavity test Salts,NaCl, KCl ; Table : 21.5 Substance deflagrate s (a) Compound fused in cavity directly Nature and colour of bead Cation Yellow, brittle bead Bi3  Yellow, soft bead which marks on paper Pb 2  Oxidisingagents like NO 3 , NO 2 chlorates Substance infusible, perform test (a) (vi) Cobalt Nitrate test Table : 21.6 Composition Colour White, brittle Sb White yellow when hot ZnO White garlic odour As 2 O3 Brown CdO Grey metallic particles attracted by magnet Fe, Ni, CO Maleable beads Ag and Sn (White), Cu (Red Result 60 3 Blue residue Green residue Al CoO. ZnO ZnO CoO. MgO MgO E3 Pink dirty residue CoO. Al2 O3 Blue residue PO43  in absence of NaCoPO4 Al. (2) Wet tests for acid radicals : Salt or mixture is treated with dil. H 2 SO 4 and also with conc. H 2 SO 4 separately and by observing the types of gases evolved. Confirmatory tests of anions are performed. ID flakes) (b) Compound mixed with Na 2 CO 3 Crystalline Table : 21.7 Observations with Dilute H 2 SO 4 Brisk effervescence with evolution of colourless and odourless gas. Acid Radical CO 32  (carbonate) Confirmatory test U Observations Gas turns lime water milky but milkyness disappears on passing gas inexcess, Na 2 CO 3  H 2 SO 4  Na 2 SO 4  H 2 O  CO 2 D YG Ca(OH )2  CO 2  CaCO 3  H 2 O lime water milky CaCO 3  H 2 O  CO 2  Ca(HCO 3 )2 Brown fumes NO 2 (Nitrite) soluble Add KI and starch solution blue colour 2 NaNO 3  H 2 SO 4  Na 2 SO 4  2 HNO 2 ; 2 NO  O 2 (air)  2 NO 2 (brown) HNO 2  NO (colourless); 2 KI  H 2 SO 4  2 NHO 2  K 2 SO 4  2 H 2 O  2 NO  I 2 U  blue colour I 2  starch  Smell of rotten eggs (H 2 S smell) on ST heating S 2  (sulphide) Colourless gas with pungent smell of burning sulphur Gas turn lead acetate paper black Sodium carbonate extract (SE )* + sodium nitroprusside – purple colour, Na 2 S  H 2 SO 4   H 2 S  Na 2 SO 4 H 2 S  (CH 3 COO )2 Pb  PbS  2CH 3 COOH (black) Na 2 S  Na 2 [Fe(CN )5 NO ]  Na 4 [Fe(CN )5 NOS ] sodium nitroprusside SO 32  (sulphite) (purple) Gas turns acidified K 2 Cr2 O7 solution green [different from CO 32  ] since gas also turns lime water milky  Na 2 SO 3  H 2 SO 4  Na 2 SO 4  H 2 O  SO 2 Cr2 O72   3 SO 2  2 H   2Cr 3   3 SO 42  H 2 O (green ) Ca(OH )2  SO 2  CaSO 3 (milky) Solution gives smell of vinegar CH 3 COO  (acetate) Aq. Solution + FeCl 3 blood neutral red colour 3 CH 3 COONa  FeCl 3  Fe(CH 3 COO )3  3 NaCl neutral White or yellowish white turbidity on warming S 2 O 32  (thiosulphate) Aq. Solution + (red) AgNO 3 white ppt. changing to black (viii) on warming , Na 2 S 2 O 3  2 AgNO 3   Ag 2 S 2 O 3  2 NaNO 3 white ppt. black ppt. Table : 21.8 Observation with concentrated H 2 SO 4 Acid Radical Colourless pungent gas giving white fumes with aq. NH 4 OH Cl  (chloride) Confiramatory Test E3 Observation 60 Ag 2 S 2 O 3  H 2 O  Ag 2 S  H 2 SO 4 Add MnO 2 in the same test tube and heat–pale green Cl 2 gas (i) S.E.+ HNO 3  AgNO3 solution –white ppt. soluble in aq. NH 3 (ii) Reddish brown fumes ID Chromyl chloride test (iii) Br  (bromide) Add Mn 2 O and heat –yellowish brown Br2 gas (iv) S.E.+ HNO 3  AgNO3 solution –pale yellow ppt. partially soluble aq. NH 3 (v) Violet pungent vapours turning starch paper blue. I  (iodide) U Layer test (vi) S.E.+ HNO 3  AgNO3 yellow ppt. insoluble in aq. NH 3 (vii) D YG Layer test (vi) Brown pungent fumes intensified by the addition of Cu- turnigs. NO 3 (nitrate) Ring test (viii) Colourless gases turning lime water milky and burning with blue flame. C 2 O 42  (oxalate) Acidified KMnO 4 solution is decolorised (ix) Reactions S. E.  CH 3 COOH  CaCl 2 white ppt. decolorising acidified KMnO 4 solution (x) Chloride : (i) KCl  conc.H 2 SO 4  KHSO 4  HCl U HCl  NH 3  NH 4 Cl (white fumes)  4 HCl  MnO2  MnCl2  Cl2  2 H 2O ST (ii) KCl  AgNO3  AgCl   KNO 3 white ppt. soluble heat K2Cr2O7 (solid)  conc. H 2 SO 4   reddish brown vapours of chromyl-chloride (CrO2Cl 2 ). Pass these vapours into NaOH , when yellow CH 3 COOH Na 2CrO4 solution is formed. On adding and (CH 3 COO )2 Pb, yellow ppt. of lead chromate (PbCrO4 ) is formed. conc. CrO3  2 HCl  CrO2Cl2  2 H 2O CrO2Cl 2  4 NaOH  Na 2CrO4  2 NaCl  2 H 2O Na 2CrO4  (CH 3 COO )2 Pb  PbCrO4  2CH 3 COONa Bromide : (iv)  KBr  conc. H 2 SO 4  KHSO 4  H ;  4 HBr  MnO2  Br2  2 H 2 O  MnBr2 (iii) Chromyl- chloride test : +  K2Cr2O7  2 H 2 SO 4  2 KHSO 4  2CrO3  H 2O yellow ppt. AgCl  aq. 2 NH 3  [ Ag(NH 3 )2 ] Cl Chloride  KCl  conc.H 2 SO 4  KHSO 4  HCl ; (v) NaBr  AgNO 3  AgBr   NaNO 3 pale yellow ppt. AgBr  aq. 2 NH 3 [ Ag( NH 3 )2 ]Br partiallysoluble (vi) Layer Test : S. E.  Cl 2 shake water + CHCl 3  yellowish orange colour in CHCl 3 layer (CS 2 or CCl 4 can be taken decolourises acidified KMnO4. Specific test in solution 2 NaBr  Cl 2  2 NaCl  (i) Sulphate : S.E. add dil. (to decompose CO 32  until reaction Br2 orange yellow (soluble in CHCl 3 ) case of I , violet colour of I2 ceases). Add BaCl2 solution. White ppt. insoluble in conc. HNO 3 , in CHCl 3 layer, BaCl2  NaSO 4  BaSO 4  2 NaCl white ppt. 2 NaI  Cl 2   2 NaCl  I 2 (violet)  KI  conc. H 2 SO 4  KHSO 4  HI ; 2 HI  H 2 SO 4   I2 + 2 H 2 O  SO 2 (ii) Borate : lgnite the mixture containing borate, conc. H 2 SO 4. And ethanol in a china-dish with a burning splinter –green edged flame of ethyl borate. 2 Na 3 BO3  3 H 2 SO 4 2 H 3 BO3  3 Na 2 SO 4 ; NaNO 3  H 2 SO 4  NaHSO 4  HNO 3 Nitrate : (conc.)  H 3 BO 3  3 C 2 H 5 OH  (C 2 H 5 O)3 B  3 H 2 O 4 HNO 3  4 NO 2  O 2 2 H 2 O ; brown fumes ethanol Cu  4 HNO 3   Cu (NO 3 )2  2 NO 2  2 H 2 O (viii) Ring test : To water extract (all NO 3 are water soluble) add Cu freshly prepared FeSO 4 solution and then conc. H 2 SO 4 carefully by the the interface between the two liquids is formed.  Na3 PO4  12(NH 4 )2 MoO4  24 HNO3  U SO 42  H 2O D YG [Fe (H 2 O)6 ] SO 4  NO [Fe(H 2 O)5 NO ] crystalline ppt. confirms yellow ppt. 3 Fe2 (SO 4 )3  2 NO  4 H 2O 2 Oxalate : Na 2 C2 O4  H 2 SO 4   Na 2 SO 4  H 2O  CO  CO 2 Arsenic also gives this test. Hence presence of phosphate should also be checked after group II. (iv) Fluoride : Sand +salt (F  ) +conc. H 2 SO 4 ; heat and bring a water wetted rod in contact with vapours at the mouth of the test tube. A white deposit on the rod shows the presence to F  CO burns with blue flame and CO 2 turns lime water milky. (ix)  2 MnO4  16 H  (violet) In presence of Cu 2  , perform this test in a test tube since salts are not volatile. (iii) S. E.  HNO 3  ammonium molybdate solution. Heat, yellow (NH 4 )3 PO4. 12 MoO3  21 NH 4 NO 3  3 NaNO 3  12 H 2 O 2 NaNO 3  H 2 SO 4  2 NaHSO 4  2 HNO 3 ; 2 HNO3  6 Fe SO 4  3 H 2 SO 4  2 burns with green flame (volatile) ID side of the test- tube. A dark brown ring of [Fe (H 2 O)5 NO ]2 SO 42 at 5 C 2 O 42  60 (vii) E3 Iodide : CaC 2 O 2 white ppt. instead of CHCl 3 ); In CaCl 2  NaC2 O4   CaC2O4  2 NaCl (x) 10 CO 2  2 Mn 2  8H 2O colourless  NaF  H 2 SO 4  NaHSO 4  HF  SiO2  4 HF  SiF4  2 H 2 O 3 SiF4 4 H 2 O   2 H 2 SiF6  H 4 SiO4 white (3) Wet tests for basic radicals : Analysis of Basic Radicals Table : 21.9 Ag  , Hg 22  (I), Pb 2  ST I Basic radicals U Group II Group reagent dil HCl Ppt. as Chloride Explanation ( AgCl, Hg 2 Cl 2 , PbCl2 ) precipitated. Others have higher values hence not precipitated. values of chlorides are low, hence K SP Cu 2  , Cd 2  , Pb 2  , H 2 S gas in presence Sulphides ( CuS , As 2 S 3 K SP Hg 2  (II), Bi 3  , As 3  , of dil. HCl etc.) precipitated by low [S 2 ] ion. HCl (with Al 3  , Cr 3  , Fe 3  values of sulphides are low hence common H  ion) decreases ionization of Sb 3  , Sn 2  III K SP H2S which gives low [S 2 ]. Hence II group is precipitated. Others with higher K SP values not precipitated. NH 4 OH in presence of NH 4 Cl Hydroxide, Al(OH )3 etc. K SP values of Al(OH )3 etc. are low. NH 4 Cl (with common NH 4 ion) decreases ionization of NH 4 OH giving low [OH  ]. Hence group III is precipitated. IV Zn 2  , Ni 2  , Mn 2  , Co 2  H2S in Sulphides ( ZnS etc.) ammonical medium K SP values of sulphides of group IV are high hence precipitation takes place in higher [S 2 ]. Basic medium increases ionization of H 2 S increasing [S 2 ] hence precipitation of group IV. (NH 4 )2 CO 3  NH 4 Cl Carbonates Ca 2  , Ba 2  , Sr 2  ( CaCO 3 etc.) K SP values of carbonate are less than that of group VI (Mg 2 ) hence precipitation 60 V before Mg 2 . Mg 2  , (Na  , K  included) 0 (Zero) also NH 4 OH  Na 2 HPO4 (only for Mg 2 ) – NH 4 – White ppt. (MgHPO4 ) – Chemical reactions involved in the tests of basic radicals Group I : When dil. HCl is added to original solution, insoluble chlorides of lead, silver mercurous mercury are precipitated. Pb(NH 3 )2  2 HCl  PbCl2  2 HNO 3 ; Tested independently from original solution. E3 VI (iii) On adding KI to the complex solution, yellow precipitate is obtained. Ag(NH 3 )2 Cl  KI  AgI  KCl  2 NH 3 Hg 22  (mercurous) ID AgNO3  HCl  AgCl  HNO 3 Hg(NO 3 )2  2 HCl  HgCl2  2 HNO 3 Pb (lead) (i) PbCl 2 is soluble in hot water and on cooling white crystals are again formed. (ii) The solution of PbCl 2 gives a yellow precipitate with potassium chromate solution which is insoluble in acetic acid but soluble in sodium hydroxide. (i) Hg 2 Cl 2 turns black with NH 4 OH , Hg2 Cl 2  2 NH 4 OH Hg  Hg( NH 2 )Cl  NH 4 Cl  2 H 2 O    Black D YG U 2+ PbCl2  K 2 CrO4  PbCrO4  2 KCl ; yellow ppt. PbCrO4  4 NaOH  Na 2 PbO2  Na 2 CrO4  2 H 2 O (iii) The solution of potassium iodide solution. PbCl 2 forms a yellow precipitate with PbCl2  2 KI  PbI2  2 KCl Yellow ppt. U (iv) White precipitate of lead sulphate is formed with dilute H 2 SO 4. The precipitate is soluble in ammonium acetate, ST PbCl2  H 2 SO 4  PbSO 4  2 HCl ; PbSO 4  2CH 3 COONH 4  Pb(CH 3 COO)2  (NH 4 )2 SO 4 Ag (silver) + (i) AgCl dissolves in ammonium hydroxide, AgCl  2 NH 4 OH  Ag( NH 3 ) 2 Cl  2 H 2 O Diammine silver (I) chloride (ii) On adding dilute HNO 3 to the above solution, white precipitate is again obtained Ag( NH 3 ) 2 Cl  2 HNO 3  AgCl  2 NH 4 NO 3 Whiteppt. (ii) The black residue dissolves in aqua-regia forming mercuric chloride. 3 HCl  HNO 3  NOCl  2 H 2 O  2Cl 2 Hg(NH 2 )Cl  6 Cl  2 HgCl2  4 HCl  N 2 Hg  2Cl  HgCl2 (iii) The solution of HgCl2 precipitate with stannous chloride. forms white or slate-coloured 2 HgCl2  SnCl 2  Hg 2 Cl 2  SnCl 4 white ppt. Hg 2 Cl 2  SnCl 2  2 Hg  SnCl 4 Grey ppt. (iv) The solution of HgCl 2 with copper turning forms a grey deposit. HgCl2  Cu  Hg  CuCl 2 Grey ppt. Group II : When hydrogen sulphide is passed in acidified solution, the radicals of second group are precipitated as sulphides. The precipitate is treated with yellow ammonium sulphide. The sulphides of IIB are first oxidised to higher sulphides which then dissolve to form thio-compounds. Ag 2 S 3  2(NH 4 )2 S 2  2(NH 4 )2 S  As 2 S 5 Sb 2 S 3  2(NH 4 )2 S 2  2(NH 4 )2 S  Sb 2 S 5 SnS  (NH 4 )2 S 2 (NH 4 )2 S  SnS 2 As2 S 5  3( NH 4 )S  2( NH 4 )3 AsS4 Ammonium thioarsena te Sb 2 S 5  3( NH 4 )2 S  2( NH 4 )2 SbS 4 Part II : The solution of BiCl 3 is treated with sodium stannite when a black precipitate of metallic bismuth is formed, 2 BiCl3  3 Na 2 SnO 2  6 NaOH   Ammonium thioantimonate SnS 2  ( NH 4 )2 S  ( NH 4 )2 SnS 3 Sod. stannite 3 Na 2 SnO 3  2 Bi  6 NaCl  3 H 2 O Ammonium thiostanna te All the three are soluble. In case, the precipitate does not dissolve in yellow ammonium sulphide, it may be either HgS or PbS or Bi2 S 3 or CuS or CdS. The precipitate is heated with dilute HNO 3. Except HgS , all other Sod. stannate Cu (copper) : Blue coloured solution is acidified with acetic acid. 2+ When potassium ferrocyanide is added a chocolate coloured precipitate is formed, Cu(NH 3 )4 (NO 3 )2  4 CH 3 COOH   sulphides of IIA are soluble. 60 Cu(NO 3 )2  4 CH 4 COONH 4 3 PbS  8 HNO3 3 Pb(NO 3 )2  2 NO  3 S  4 H 2O 2Cu ( NO 3 )2  K 4 [Fe(CN )6 ]  Cu 2 [Fe(CN )6  4 KNO 3 Bi2 S 3  8 HNO3 2 Bi(NO 3 )3  2 NO  3 S  4 H 2 O Chocolate ppt. 3CuS  8 HNO3 3Cu(NO 3 )2  2 NO  3 S  4 H 2O Cd (cadmium) : H 2 S is passed through colourless solution. The 2+ 3CdS  8 HNO3 3Cd (NO 3 )2  2 NO  3 S  4 H 2 O 2+ E3 appearance of yellow precipitate confirms the presence of cadmium, Hg (mercuric) Cd ( NH 3 )4 ( NO 3 )2  H 2 S  CdS  2 NH 4 NO 3  NH 3 HgS is dissolved in aqua-regia, Yellow ppt. 3 HgS  2 HNO3  6 HCl 3 HgCl2  3 S  2 NO  4 H 2 O The solution is divided into two parts: ID Part I : Stannous chloride solution reduces HgCl2 first into white Hg2 Cl 2 and then to grey metallic mercury. 3+ Part II : Copper displaces Hg from HgCl2 which gets coated on copper turnings as a shining deposit. Pb (lead) As2 S 5  10 HNO 3  2 H 3 AsO4  10 NO 2  2 H 2 O  5 S U 2+ Group IIB : In case the precipitate dissolves in yellow ammonium sulphide, the tests of the radicals arsenic, antimony and tin are performed. The sulphide is treated with concentrated hydrochloric acid. Antimony and tin sulphide dissolve while arsenic sulphide remains insoluble. As (arsenic) : The insoluble sulphide is treated with concentrated nitric acid which is then heated with ammonium molybdate. Yellow precipitate of ammonium arsenomolybdate is formed. Arsenic acid In case the sulphide dissolves in dilute HNO 3 , a small part of the D YG solution is taken. Dilute H 2 SO 4 is added. If lead is present, a white precipitate of lead sulphate appears, Pb(NO 3 )2  H 2 SO 4 PbSO4  2 HNO 3 (White ppt.) In absence of lead, the remaining solution is made alkaline by the addition of excess of NH 4 OH. Bismuth forms a white precipitat of Bi(OH )3 , copper forms a deep blue coloured solution while cadmium forms a colourless soluble complex, Bi( NO 3 )3  3 NH 4 OH   Bi(OH )3  3 NH 4 NO 3 Whiteppt. U Cu ( NO 3 )2  4 NH 4 OH [Cu ( NH 3 )4 ] ( NO 3 )2  4 H 2 O; H 3 AsO4  12(NH 4 )2 MoO4  21HNO 3   Yellow ppt. Sn or Sn (tin) : Solution of sulphide in concentrated HCl is reduced 2+ SnS 2  4 HCl   SnCl 4 2 H 2 S White ppt. SnCl 4  Fe   SnCl 2  FeCl4 Grey HgCl2 solution is added to above solution which gives first a white precipitate that turns to grey. 2 HgCl2  SnCl 2  HgCl2  SnCl 4 White ppt. ST Cd ( NO 3 )2  4 NH 4 OH  [Cd ( NH 3 )4 ]( NO 3 )2  4 H 2 O 3+ (bismuth) : Hg 2 Cl 2  SnCl 2  2 Hg  SnCl 4 Tetrammin e cadmium nitrate (colourless solution) The precipitate dissolves 4+ with iron fillings or granulated zinc. Tetrammin e cupric nitrate (deep blue solution) Bi (NH 4 )3 AsO4. 12 MoO3  21 NH 4 NO 3  12 H 2 O Grey Sb (antimony) : Filtrate of sulphide in concentrated HCl is divided into two parts. Part I : On dilution with excess of water, a white precipitate of antimony oxychloride is obtained. 2+ in dilute HCl, Bi(OH )3  3 HCl  BiCl3  3 H 2 O Part I : Addition of excess of water to BiCl3 solution gives a white precipitate due to hydrolysis. BiCl3  H 2 O  BiOCl  2 HCl Bismuth Oxychloride (Whiteppt.) SbCl 3  H 2 O   SbOCl  2HCl White ppt. Part II : H 2 S is circulated. Orange precipitate is formed, 2 SbCl 3  3 H 2 S  Sb 2 S 3  6 HCl Orange ppt. Group III : Hydroxides are precipitated on addition of excess of ammonium hydroxide in presence of ammonium chloride. AlCl3  3 NH 4 OH  Al(OH )3  3 NH 4 Cl ZnCl 2  2 NaOH   Zn(OH )2  2 NaCl White ppt. Zn(OH )2  2 NaOH  Na 2 ZnO2  2 H 2 O Gelatinous ppt. (Soluble) On passing H 2 S , white precipitate of zinc sulphide is formed CrCl3  3 NH 4 OH   Cr(OH )3  3 NH 4 Cl Green ppt. Na 2 ZnO2  H 2 S  ZnS  2 NaOH White ppt. FeCl3  3 NH 4 OH   Fe(OH )3  3 NH 4 Cl Mn Fe (iron) : The brownish red precipitate dissolves in dilute HCl. The solution is divided into two parts. 3+ Part I : K 4 [Fe(CN )6 ] solution is added which forms deep blue solution or precipitate. Manganese sulphide dissolves in HCl MnS  2 HCl  MnCl2  H 2 S On heating the solution with NaOH and Br2 -water, manganese dissolve gets precipitated. 60 Brownish red ppt. (manganese) : 2+ MnCl2  2 NaOH   Mn(OH )2  2 NaCl Fe(OH )3  3 HCl  FeCl3  3 H 2 O 4 FeCl3  3 K 4 [Fe(CN )6 ]  Fe4 [Fe(CN )6 ]3  12 KCl E3 Mn(OH )2  O   MnO2 H 2 O The precipitate is treated with excess of nitric acid and PbO2 or Prussian blue Part II : Addition of potassium thiocyanate solution gives a blood red colouration. Pb3 O4 (red lead). The contents are heated. The formation of permanganic acid imparts pink colour to the supernatant liquid. 2 MnO2  4 HNO 3  2 Mn(NO 3 )2 2 H 2O  O2 FeCl3  3 KCNS  Fe(CNS )3  3 KCl 2 Mn(NO 3 )2  5 Pb3 O4  26 HNO 3   ID Blood red colour Cr (chromium) : The green precipitate is fused with fusion mixture (Na 2 CO 3  KNO 3 ). The fused product is extracted with water or the 3+ precipitate is heated with NaOH and bromine water. Permangani c acid (pink) The above test fails in presence of HCl. Ni (nickel) and Co (cobalt) The black precipitate is dissolved in aqua- regia. 2+ 2+ U 2Cr(OH )3  3 KNO  2 Na 2 CO 3   2 HMnO4  15 Pb (NO3 )2  12 H 2 O 2 Na 2 CrO4  3 KNO 2  2CO 2  3 H 2 O D YG or 2 NaOH  Br2  NaBrO4  NaBr  H 2 O 3 NiS  6 HCl  2 HNO3   2 NiCl2  2 NO  3 S  2 H 2O 3CoS  6 HCl  2 HNO 3   3CoCl 2  2 NO  3 S  4 H 2 O NaBrO  NaBr  [O] The solution is evaporated to dryness and residue extracted with dilute HCl. It is divided into three parts. 2Cr(OH )3  4 NaOH  3[O]  2 NaCrO4  5 H 2 O Part I : Add NH 4 OH (excess) and dimethyl glyoxime. A rosy red precipitate appears, if nickel is present, The solution thus obtained contains sodium chromate. The solution is acidified with acetic acid and treated with lead acetate solution. A yellow precipitate appears. Na 2 CrO4  Pb(CH 3 COO )2  PbCrO4  2CH 3 COONa CH 3  C  NOH  2 NH 4 OH  NiCl2  2 | CH 3  C  NOH Yellow ppt. U Al (aluminium) : The gelatinous precipitate dissolves in NaOH , 3+ Al(OH )3  NaOH  NaAlO2  2 H 2 O Soluble ST The solution is boiled with ammonium chloride when Al(OH )3 is again formed. NaAlO2  NH 4 Cl  H 2 O   Al(OH )3  NaCl  NH 3 Group IV : On passing H 2 S through the filtrate of the third group, sulphides of fourth group are precipitated. NiS and CoS are black and insoluble in concentrated HCl while MnS (buff coloured), ZnS (colourless) are soluble in conc. HCl. Zn 2+ (zinc) : The sulphide dissolves in HCl. ZnS  2 HCl  ZnCl 2  H 2 S When the solution is treated with NaOH , first a white precipitate appears which dissolves in excess of NaOH OH | CH 3  C  N | CH 3  C  N  O Ni O  N  C  CH 3 |  2 NH 4 Cl  2 H 2 O N  C  CH 3 | OH Part II : Add CH 3 COOH in excess and KNO 2. The appearance of yellow precipite confirms the presence of cobalt. KNO 2  CH 3 COOH  CH 3 COOK  HNO 2 CoCl 2  2 KNO 2  Co (NO 2 )2  2 KCl Co (NO 2 )2  2 HNO 2  Co (NO 2 )3  NO  H 2 O Co (NO 2 )3  3 KNO 2  K3 [Co (NO 2 )6 ] Part III : Solution containing either nickel or cobalt is treated with NaHCO 3 and bromine water. Appearance of apple green colour is observed, the solution is heated when black precipited is formed, which shows the presence of nickel, 2 K 2 HgI4  NH 4 Cl  4 KOH  NH 2 Hg CoCl 2  2 NaHCO 3   Co (HCO 3 )2  2 NaCl Co (HCO 3 )2  4 NaHCO3  Na 4 Co (CO 3 )3  3 H 2 O  3CO 2 I Iodide of Millon's base (Brown ppt.) Br2  H 2 O  2 HBr  O 2 Na 4 Co (CO 3 )3  H 2 O  O  2 Na 3 Co (CO 3 )3  2 NaOH 2 NiCO 3  [O]  Ni2 O 3  2CO 2 (Black) Group V : Ammonium carbonate precipitates V group radicals in the form of carbonates are soluble in acetic acid. BaCO3  2CH 3 COOH (CH 3 COO)2 Ba  CO 2  H 2 O ID SrCO 3  2CH 3 COOH (CH 3 COO)2 Sr  CO 2  H 2 O CaCO 3  2CH 3 COOH (CH 3 COO)2 Ca  CO 2  H 2 O Ba (barium) : Barium chromate is insoluble and precipitated by the 2+ potassium chromate solution, sulphate Sr (Strontium) : Strontium sulphate is insoluble and precipitated by addition of ammonium sulphate solution, D YG the Sr (CH 3 COO )2  ( NH 4 )2 SO 4  SrSO 4  2CH 3 COONH 4 White ppt. Ca (calcium) : Calcium oxalate is insoluble and precipitated by the addition of ammonium oxalate. 2+ Ca(CH 3 COO )2  (NH 4 )2 C2 O4  CaC2 O4  2CH 3 COONH 4 White ppt. U Group VI : In the filtrate of V group, some quantity of ammonium oxalate is added as to remove Ba, Ca and Sr completely from the solution. The clear solution is concentrated and made alkaline with NH 4 OH. Disodium hydrogen phosphate is now added, a white precipitate is formed. ST MgCl2  Na 2 HPO4  NH 4 OH   Mg( NH 4 )PO4  2 NaCl  H 2 O Megnesium ammonium phosphate (White ppt.) Zero group NH 4 (ammonium) : The substance (salt or mixture) when heated with NaOH solution evolves ammonia. NH 4 Cl  NaOH   NaCl  NH 3  H 2 O white ( AgNO3 ) , copper sulphate U Ba(CH 3 COO)2  K 2 CrO4   BaCrO4  2CH 3 COOK 2+ Volumetric analysis is a quantitative analysis. It involves the measurement of the volume of a known solution required to bring about the completion of the reaction with a measured volume of the unknown solution. Titration : The process of addition of the known solution from the burette to the measured volume of solution of the substance to be estimated until the reaction between the two is just complete, is termed as titration. Thus, a titration involves two solutions; (i) Unknown solution : The solution consisting the substance to be estimated is termed unknown solution. The substance is termed titrate. (ii) Standard solution : The solution in which an accurately known amount of the reagent (titrant) has been dissolved in a known volume of the solution is termed standard solution. There are two types of reagents (titrants) : (a) Primary standards : These can be accurately weighed and their solutions are not to be standardised before use. Oxalic acid (H 2 C 2 O4.2 H 2 O) , potassium dichromate (K 2 Cr2 O7 ) , silver nitrate E3 NiCl2  2 NaHCO 3   NiCO3  2 NaCl  H 2 O  CO 2 of Volumetric analysis 60 sod. cobalti carbonate (Green colouration) addition  7 KI  KCl  3 H 2 O O Hg When a rod dipped in HCl is brought on the mouth of the test tube, fumes of ammonium chloride are formed, NH 3  HCl  NH 4 Cl White fumes To the aqueous solution of ammonium salt when Nessler’s reagents is added, brown coloured precipitate is formed. (CuSO 4.5 H 2 O) , ferrous ammonium [FeSO 4 (NH 4 )2 SO 4.6 H 2 O] , sodium thiosulphate (Na 2 S 2 O3.5 H 2 O) , etc., are the examples of primary standards. (b) Secondary standards : The solutions of these reagents are to be standardised before use as these cannot be weighed accurately. The examples are sodium hydroxide (NaOH ) , potassium hydroxide (KOH ) , hydrochloric acid (HCl) , sulphuric acid (H 2 SO 4 ) , potassium permanganate (KMnO4 ) , iodine, etc. Law of equivalence : It is applied in all volumetric estimations. According to it, the chemical substances react in the ratio of their chemical equivalent masses. Mass of substance A Chemical equivalent mass of A  Mass of substance B Chemical equivalent mass of B or Mass of substance A Chemical equivalent mass of A  Mass of substance B Chemical equivalent mass of B or gram equivalent of A  gram equivalent of B or milli-gram equivalent of A  milli-gram equivalent of B The point at which the amounts of the two reactants are just equivalent is known as equivalence point or end point. An auxiliary substance which helps in the usual detection of the completion of the titration or equivalence point or end point is termed as indicator, i.e., substances which undergo some easily detectable changes at the equivalence point are used as indicators. Methods of expressing concentrations of solutions The concentration of a solution can be expressed in various ways. (1) Percent by mass (2) Molarity (3) molality (4) Mole fraction (5) Normality Types of titrations : Titrations can be classified as : (1) Acid base titrations or acidimetry and alkalimetry (2) Oxidation reduction titrations or redox titrations (3) Precipitation titrations (4) Complexometric titrations. (1) Acid-base titrations : When the strength of an acid is determined with the help of a standard solution of base, it is known as acidimetry. Similarly, when the strength of a base (alkali) is determined with the help of a standard solution of an acid, it is known as alkalimetry. Both these titrations involve neutralisation of an acid with an alkali. In these titrations (iii) Iodimetric and iodometric titrations : The reduction of free iodine to iodide ions and oxidation of iodide ions to free iodine occurs in these titrations. H  ions of the acid combine with OH  ions of the alkali to form unionised molecules of water. This solution is first standardised before use. With the standard solution of I 2. Substances such as sulphite, thiosulphate, arsenite, etc., are estimated. (b) Iodometric titrations : In iodometric titrations, an oxidising agent is allowed to react in neutral medium or in acidic medium, with excess of potassium iodide to liberate free iodine. Alkali   Salt  Water  or H  A  B  OH  B   A   H 2 O or H   OH   H 2 O KI  I2  KI3 Potassium tri- iodide 60 Acid 2 I   I 2  2e  (oxidation) These are divided into two types : (a) Iodimetric titrations : These are the titrations in which free iodine is used. As it is difficult to prepare the solution of iodine (volatile and less soluble in water), it is dissolved in potassium iodide solution. E3 HA BOH  BA H 2 O I 2  2e   2 I  (reduction) KI  oxidising agent  I2 Free iodine is titrated against a standard reducing agent usually with sodium thiosulphate. Halogens, oxyhalogens, dichromates, cupric ion, peroxides, etc., can be estimated by this method. I2  Na 2 S 2 O3  2 NaI  Na 2 S 4 O6 ID The end point in these titrations is determined by the use of organic dyes which are either weak acids or weak bases. These change their colours within a limited range of hydrogen ion concentrations, i.e., pH of the solution. Phenolphthalein is a suitable indicator in the titrations of strong alkalies (free from carbonate) against strong acids or weak acids. Methyl orange is used as an indicator in the titrations of strong acids against strong and weak alkalies. As no indicator gives correct results in the titrations of weak acids against weak bases, such titrations are performed by some other methods (physical methods). (2) Oxidation reduction titrations : The titrations based on oxidation-reduction reactions are called redox titrations. The chemical reactions proceed with transfer of electrons (simultaneous loss or gain of electrons) among the reacting ions in aqueous solutions. Sometimes these titrations are named after the reagent used, as: (i) Permanganate titrations : These are titrations in which potassium permanganate is used as an oxidising agent in acidic medium. The medium is maintained by the use of dilute sulphuric acid. Potassium permanganate acts as a self-indicator. The potential equation, when potassium permanganate acts as an oxidising agent, is : 2CuSO 4  4 KI  Cu 2 I2  2 K 2 SO 4  I2 D YG U K 2 Cr2 O7  6 KI  7 H 2 SO 4  2 KMnO4  3 H 2 SO 4  K 2 SO 4  2 MnSO 4  3 H 2 O  5[O] or MnO4  8 H   5 e  Mn 2   4 H 2 O Before the end point, the solution remains colourless (when KMnO4 solution is taken in burette) but after the equivalence point only ST U one extra drop of KMnO4 solution imparts pink colour, i.e., appearance of pink colour indicates the end point. Potassium permanganate is used for the estimation of ferrous salts, oxalic acid, oxalates, hydrogen peroxide, etc. The solution of potassium permanganate is always first standardised before its use. (ii) Dichromate titrations : These are titrations in which, potassium dichromate is used as an oxidising agent in acidic medium. The medium is maintained acidic by the use of dilute sulphuric acid. The potential equation is K 2 Cr2 O7  4 H 2 SO 4  K 2 SO 4  Cr2 (SO 4 )3  4 H 2 O  3[O] or Cr2 O72   14 H   6 e   2Cr 3   7 H 2 O The solution of potassium dichromate can be directly used for titrations. It is mainly used for the estimation of ferrous salts and iodides. In the titration of K 2 Cr2 O7 versus ferrous salt either an external indicator (potassium ferricyanide) or an internal indicator (diphenyl amine) can be used. Cr2 (SO 4 )3  4 K 2 SO 4  7 H 2 O  3 I2 In iodimetric and iodometric titrations, starch solution is used as an indicator. Starch solution gives blue or violet colour with free iodine. At the end point the blue or violet colour disappears when iodine is completely changed to iodide. (3) Precipitation titrations : The titrations which are based on the formation of insoluble precipitates, when the solutions of two reacting substances are brought in contact with each other, are called precipitation titrations. For example, when a solution of silver nitrate is added to a solution of sodium chloride or a solution of ammonium thiocyanate, a white precipitate of silver chloride or silver thiocyanate is formed. AgNO3  NaCl  AgCl  NaNO 3 AgNO3  NH 4 CNS  AgCNS  NH 4 NO 3 Such titrations involving silver nitrate are called argentometric titrations. (4) Complexometric titrations : A titration, in which an undissociated complex is formed at the equivalence point, is called complexometric titration. These titrations are superior to precipitation titrations as there is no error due to co-precipitation. Hg 2   2SCN   Hg(SCN )2 Ag   2CN  [ Ag(CN )2 ] EDTA (ethylenediamine tetra-acetic acid) is a useful reagent which forms complexes with metals. In the form of disodium salt, it is used to estimate Ca 2  and Mg 2  ions in presence of eriochrome black- T as an indicator. Equivalent masses of acids and bases : Equivalent masses of some acids and bases are given in the following table Table : 21.10 Mol. Mass 1 36.5 Eq. Mass 36. 5 =36.5 1 3 1 63 63 =63.0 1 H SO 4 2 98 98 =49.0 2 CH COOH 1 60 60 =60.0 1 H C O.2H O 2 126 126 =63.0 2 H PO 3 98 98 =32.7 3 H PO 2 82 82 =41.0 2 H PO 1 66 66 =66.0 1 3 2 2 3 4 2 4 3 3 3 2 Table : 21.11 Mol. Mass NaOH 1 40 40 = 40 1 KOH 1 56 56 = 56 1 Ca(OH) NH OH 4 2 Eq. Mass Mass in g  1000 Molecular mass No. of moles of the solute w (iii) Molarity   No. of litresof the solution mV Molarity  molecular mass = strength of the solution (g / L) No. of moles of the solute = Molarity  No. of litres of solution Mass of the solute in g(w)  molarity  No. of litres of solution  mol. mass of solute Number of milli-moles  2 74 74 = 37 2 1 35 35 = 35 1 ST U Calculations of Volumetric analysis The following points should be kept in mind while making calculations of volumetric exercises. (i) 1 g equivalent mass of a substance reacts completely with 1 g equivalent mass of any other substance. 1 g equivalent mass of a substance means equivalent mass of the substance in grams. For example, 1 g equivalent mass of NaOH  40 g of NaOH 1 g equivalent mass of H 2 SO 4  49 g of H 2 SO 4 1 g equivalent mass of KMnO 4 in acidic medium  31.6 g of KMnO 4 1 g equivalent mass of hydrated oxalic acid  63 g of hydrated oxalic acid Note : Equivalent mass is a variable quantity and depends on the reaction in which the substance takes part. The nature of the reaction should be known before writing the gram equivalent mass of the substance. For example in the reactions. 2 NaCl  2 H 2 SO 4  2 NaHSO 4  2 HCl …..(i) 2 NaCl  H 2 SO 4  Na 2 SO 4  2 HCl …..(ii) The value of g equivalent mass of H 2 SO 4 in reaction (i) is 98 g and in reaction (ii) 49 g. No. of g equivalent of the solute w  No. of litresof the solution EV Normality  equivalent mass = strength of the solution (g/L) No. of equivalents of the solute = Normality  No. of litres of solution Mass of the solute in g(w)  Normality  No. of litres of solution  Eq. mass of the solute Molecular mass Normality n Equivalent mass Molarity Normality  n  Molarity (iv) Normality equation : When solutions A and B react completely. N A V A  N B VB Normality  U Acidity Mass of the substance in g Molecular mass of the substance Volume in litresof the substance at N.T.P. (only for gases)  22.4 Mass in g  1000 Number of milli-equivalent  Equivalent mass Number of g moles  D YG Alkali Mass of the substance in g Equivalent mass of the substance 60 HNO 2  E3 HCl Basicity ID Acid (ii) Number of g equivalents Normality of A  volume of A  Normality of B  volume of B or Strength A Strength B  VA   VB Eq. mass A Eq. mass B Wt. of metal hydroxide Eq. wt. of metal hydroxide  wt, of metal oxide Eq. wt. of metal oxide  Eq. wt of metal  Eq. wt of OH Eq. wt. of metal  Eq. wt of O 2  (v) When the solution is diluted, the following formulae can be applied : N 1 V1  N 2 V2 or M 1 V1  M 2 V2 or S 1 V1  S 2 V2 Before dilution = After dilution (vi) If a number of acids are mixed, the combined normality of the mixture, N x , is given N x Vx  N 1 V1  N 2 V2  N 3 V3 ...... Where V x is the total volume of the mixture, N 1 and V1 are the normality and volume respectively of one acid, N 2 and V 2 of the second acid and so on.  Glass rod should never be used in flame test as it gives a golden yellow colour due to sodium present in it. An asbestos fibre can be safely used in place of platinum wire.  The transparent bead in borax bead test is made of NaBO + B O.  Filter ash test is an alternative to cobalt nitrate test and gives 2 2 3 better results.  Both CO and SO turn lime water milky. 2 2 Ca(OH )2  CO 2  CaCO 3  H 2 O (Milkiness) 60 Ca(OH )2  SO 2  CaSO 3  H 2 O (Milkiness)  Eq. wt. of KMnO is different in acidic, alkaline and neutral medium 4 ST U D YG U ID E3 i.e., 31.6, 158 and 52.67 respectively.