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JEE Main Mock Test Series 2020 & Previous Year Papers

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QUALITATIVE ANALYSIS OF ORGANIC COMPOUNDS 
This is used to detect nitrogen, halogen and sulphur present in organic compound.
(a) Sodium Extract: Aqueous solution containing soluble sodium salt of the elements i.e NaCl, Na2S and NaCNS formed by fusion of compound with sodium metal.
(b) Formation of Sodium Extract: It is a two step process
Step 1: Organic compounds are fused with dry sodium in a fusion-tube
Step 2: Fused mass after extraction with water is boiled and filtered.
(c) Use of Sodium Extract: Sodium extract (S.E.) is used to detect elements (other than C and H) and the tests are given in the table.

ElementSodium Extract (S.E.)Confirmed Test
 Nitrogen 
 Na + C + N +Δ→ NaCl
 S.E.+ FeSO+NaOH, boil and cool
                         +
 FeCl3 + conc. HCl → Blue/ green colour
 Reactions Involved: NEET Notes | EduRev
 Sulphur 
 2Na + S → Na2S
 (i) S.E. + sodium nitroprusside → Violet Colour
 (ii)  S.E + CH3CO2H + (CH3CO2)Pb → black ppt.
 Reactions Involved:
 NEET Notes | EduRev
 Halogen Na +X + Δ→ NaX
 (X = Cl, Br, I)
 S.E. + HNO3+AgNO3
 (i) White ppt soluble in aq NH3 confirms Cl.
 (ii) Pale yellow ppt partially soluble in aq. NH3   confirms Br.
 (iii) Yellow ppt insoluble in aq. NH3 confirms I.
 Reactions Involved:
 NEET Notes | EduRev
 Nitrogen and sulphur   together Na+ C + N + S+ Δ→  NaCNS
 with excess of Na the thiocyanate   formed  decomposes into cyanide and   sulphide.
 NaCNS  + 2Na → NaCN +Na2S
 
 
 As in test for nitrogen; instead of green or blue   colour, blood red colouration confirms presence   of N and S both.
 Reactions Involved:
 NEET Notes | EduRev


QUALITATIVE ANALYSIS OF INORGANIC SALTS
1. Physical Examination of Salts/Mixture

ObservationInference
 1. Substance is coloured 
 (i) Blue Copper salt
 (ii) Dark green Chromium salt
 (iii) Green Salts of Fe(II), Ni, Cu or Cr
 (iv) Light yellow or brown Salts of Fe(III)
 (v) Dark brown PbO2,Bi2S3
 (vi) Light pink  Salts of Mn
 (vii) Pink Salts of Co
 (viii) Red HgO, HgI2,Pb3O4
 (ix) Orange red  Sb2S3
 2. Substance is deliquescent CaCl2,ZnCl2,MgCl2, MnCl2, nitrites, nitrates
 3. Substance is heavy   Salts of Pb, Hg and Ba
 4. Substance is light Carbonates of Bi, Mg, Al, Zn, Ca, Sr


2. Effect of Heating

ObservationInference
 1. Substance melts Salts of alkali metals and salts having water of     crystallisation.
 2. Substance decripitates (crackling noise) NaCl, KI, Pb(NO3)2 and Ba(NO3)2
 3. Substance swells (due to loss of water of crystallisation) Alums, borates and phosphates
 4. The substance sublimes and the colour of sublimate is         
 
 (i) White HgCl2, Hg2Cl2,NH4X, AlCl3, As2O3, Sb2O3
 (ii) Yellow As2S3 and HgI(turns red when rubbed with glass   rod).
 (iii) Blue black and violet vapours Iodides
 5. A residue (generally oxide) is left and its colour is 
 (i) Yellow (hot) and  white (cold)     ZnO
 (ii) Reddish brown (hot); yellow (cold) PbO
 (iii) Black (hot); Red (cold) HgO, Pb3O4
 (iv) Black (hot); Red brown (cold) Fe2O3
 6. Gas is evolved 
 (A) Colourless and odourless              
 (i) O2 - rekindles a glowing splinter Alkali nitrates (2KNO3 → 2KNO2 + O2)
 (ii) CO2 - turns lime water milky Carbonates and oxalates (CaCO3 → CaO + CO2)
 (iii) N2 Ammonium nitrite (NH4NO2 → N+ 2H2O)
 (B) Colourless gas with odour 
 (i) NH3 - Turns red litmus blue and mercurous nitrate paper   black Ammonium salts (NH4)2SO4 → NH4HSO4 + NH3
 (ii) SO2 - Smell of burning sulphur, turns acidified K2Cr2O7   paper green Sulphites and thiosulphates
 CaSO→CaO + SO2
 (iii) HCl - Pungent smell, white fumes with ammonia Hydrated chlorides
 CaCl2.6H2O → Ca(OH)2 + 4H2O + 2HCl
 (iv) H2S - smell of rotten eggs, turns lead acetate paper black Sulphides
 Na2S + 2H2O → 2NaOH + H2S
 (C)  Coloured gas 
 (i) NO2 - Brown, turns starch iodide paper blue          Nitrites and nitrates of heavy metals
 2Cu(NO3)2 → 2CuO + 4NO2 + O2
 (ii) Br2 - Reddish brown        Bromides
 2CdBr2 + O2 → 2CdO + 2Br2
 (A) Turns starch paper yellow 
 (B) turns starch iodide paper blue 
 (iii) I2 - Violet, turns starch paper blue        Iodides
 2CdI2 + O2 → 2CdO + 2I2
 (iv) Cl2 - Greenish yellow Chlorides
 (A) bleaches moist litmus paper CuCl+ H2O → CuO + 2HCl
 CuO + 2HCl → Cu + H2O + Cl2
 (B) bleaches indigo solution 
 (C) turns starch iodide paper blue 

3.  Flame test

Metals Colour
 Li crimson red
 Na golden yellow
 K Violet
 Ca Brick red
 Sr Crimson
 Ba apple green


TEST FOR ANIONS
1. Carbonate (CO32- )
(i) Dilute HCl : gives effervescence, due to the evolution of carbon dioxide.

CO32- + 2H+ → CO2­ + H2O
The gas gives turbidity with lime water and baryta water.
CO+ Ca2+ + 2OH- → CaCO3 ¯ + H2O
CO2 + Ba2+ + 2OH-→ BaCO¯ + H2O
On prolonged passage of carbon dioxide in lime water, the turbidity slowly disappears due to the formation of soluble hydrogen carbonate.
CaCO3  ¯→ + CO+ H2O → Ca(HCO3)2

(ii) Barium chloride or Calcium chloride solution: White ppt of barium or calcium carbonate is obtained, which is soluble in mineral acid.

CO32- + Ba2+ → BaCO3 ¯
CO32- + Ca2+ → CaCO3 ¯

(iii) Silver nitrate solution: White ppt of silver carbonate is obtained.

CO32- + 2Ag+ → Ag2CO3¯
The ppt so obtained is soluble in nitric acid and in ammonia. The ppt becomes yellow or brown on addition of excess reagent and same may also happen if the mix is boiled, due to the formation of silver oxide
Ag2CO3¯ → Ag2O ¯ + CO2 ­

2. Sulphites (SO32-)
(i) Dilute HCl or Dilute H2SO4decomposes with the evolution of sulphur dioxide
SO32- + 2H+ → SO2 + H2O
The gas has a suffocating odour of burning sulphur.
(ii) Acidified potassium dichromate solution: Turns filter paper moistened with acidified potassium dichromate solution,  green due to the formation of  Cr3+ions.
(iii) Lime water: On passing the gas through lime water, a milky ppt is formed.
Precipitate dissolves on prolonged passage of the gas, due to the formation of hydrogen sulphite ions.
(iv) Barium chloride or Strontium chloride solution: Gives white ppt. of barium or strontium sulphite.

3. Sulphide (S-2)
(i) Dil. HCl or Dil. H2SO4: A colourless gas smelling of rotten eggs (H2S) is evolved.
S2- + 2H+ →  H2
(ii) The gas turns lead acetate paper black
(iii) Gives yellow ppt. with CdCO3
Na2S + CdCO3 → CdS¯ + Na­2CO3
(iv) Silver nitrate solution: black ppt. of silver sulphide insoluble in cold but soluble in hot dil nitric acid.
S2- + 2Ag→ Ag2S ¯
(v) Sodium nitroprusside solution: Turns sodium nitroprusside solution purple
Na2S + Na2[Fe(CN)5NO] → Na4[Fe(CN)5NOS]

4. Nitrites (NO2-)
(i) Dil HCl and Dil. H2SO4Adding to solid nitrite in cold yields pale  blue liquid (due to the presence of free nitrous acid HNOor its anhydride N­2O3) & the evolution of brown fumes of nitrogen dioxide, the latter being largely produced by combination of nitric oxide with the oxygen of the air
(ii) Silver nitrate solution: White crystalline ppt. is obtained
NO2- + Ag→ AgNO2¯
(iii) Turns acidified KI - starch paper blue
2KI + 2NO2 → 2KNO2 + I2 ­
Starch + I → Blue colour
(iv) Brown ring test: When the nitrite solution is added carefully to a conc. solution of Iron(II) sulphate acidified with dil acetic acid or with dilute sulphuric acid, a brown ring is formed, due to the formation of [FeNO]SO4  at the junction of the two liquids.
5. Acetate (CH3COO-)
(i) Dilute Sulphuric Acid: Smell of vinegar is observed.
CH3COO- + H+ → CH3COOH ­
The following test is performed with the aqueous salt solution.
(ii) Iron (III) Chloride Solution: Gives  deep - red colouration
CH3COONa + FeCl3  → (CH3COO)3Fe + 3NaCl
Brown colour

6. Thiosulphates 
(i) Dil Hydrochloric acid: Gives sulphur & sulphur di oxide
(ii) Silver nitrate solution: Gives white ppt. of silver thiosulphate.
S2O32-+ 2Ag+ → Ag2S2O3 ¯
The ppt. is unstable, turning dark on standing, when silver sulphide is formed.
Ag2S2O3¯ + H2O → Ag2S + H2SO4
(iii) Lead acetate or Lead nitrate solution: Gives white ppt.
S2O32-+ Pb2+ → PbS2O3 ¯
On boiling it turns black due to the formation of PbS.
PbS2O3 ¯ + H2O →PbS ¯ + 2H+ + SO42 
7. Chloride (Cl-)
(i) Conc. H2SO4 : decomposes with the evolution of HCl.
Cl- + H2SO4 → HCl  + HSO

Gas so produced
(1) Turns blue litmus paper red
(2) Gives white fumes of NH4Cl when a glass rod moistened with ammonia solution is brought near the mouth of test tube.

(ii) Silver nitrate solution: White, curdy ppt. of AgCl insoluble in water & in dil .nitric acid, but soluble in dilute ammonia solution.
(iii) Chromyl chloride test: When a salt containing chloride ion is heated with K2Cr2O7 and conc. H2SOorange red fumes of chromyl chloride (CrO2Cl2) are formed.
K2Cr2O7 + 4NaCl +  6H2SO4 → 2KHSO4 + 4NaHSO4 + 2CrO2Cl2 ­ + 3H2O
                                                                               orange – red fumes
Chlorides of mercury, owing to their slight ionization, do not respond to this test and only partial conversion to CrO2Cl2 occurs with the chlorides of lead, silver, antimony and tin.
When chromyl chloride vapours are passed into sodium hydroxide a yellow solution of sodium chromate is formed which when treated with lead acetate gives yellow ppt. of lead chromate.
 NEET Notes | EduRev

8. Bromide (Br-)
(i) Conc. H2SO4: Gives reddish brown vapours of bromine accompanying the hydrogen bromide.
(ii) Manganese dioxide and conc. sulphuric acid: When a mix of solid bromide,
MnOand conc. H2SO4 is heated reddish brown vapours of bromine are evolved.
2KBr + MnO2 + 2H2SO→ Br2 ­ + K2SO+ MnSO4 + 2H2O
The following tests are performed with the aqueous salt solution.
(iii) Silver nitrate solution: Pale yellow ppt. of silver bromide is obtained. This ppt. is sparingly soluble in dil but readily soluble in conc. ammonia solution and insoluble in dil. HNO3.
(iv) Lead acetate solution: White crystalline ppt. of lead bromide which is soluble in
boiling water.                  

9. Iodide (I-)
(i) Conc. H2SO4Gives violet vapours of iodine
(ii) Silver nitrate solution: Yellow  ppt. of silver iodide AgI, very slightly soluble in conc. ammonia solution and insoluble in dil nitric acid.

10. Nitrate (NO3- )
(i) Conc H2SO4Gives reddish - brown vapours of nitrogen dioxide
4NO3+ 2H2SO4 →  4NO2­ + 2SO42- + 2H2O + O
(ii) Brown ring test: When freshly saturated solution of iron (II) sulphate is added to nitrate solution and conc. H2SO4 is poured slowly down the side of the test - tube, a brown ring is obtained.
2NO3- + 4H2SO4 + 6Fe2+ → 6Fe3+ +2NO + 4SO4–2 + 4H2O
Fe2+ + NO­ → [Fe(NO)]2+
On shaking and warming the mix, the brown colour disappears, nitric oxide is evolved and a yellow solution of Iron(III) ions remains.

11. Sulphate (SO42-)
(i) Barium chloride solution: White ppt. of barium sulphate BaSOinsoluble in warm dil. hydrochloric acid and in dilute nitric acid, but moderately soluble in boiling, conc. hydrochloric acid.
(ii) Mercury (II) nitrate solution: Gives yellow ppt. of basic mercury (II) sulphate

12. Chromate CrO42 -and Dichromate (Cr2O)
(i) Barium chloride solution: Pale - yellow ppt. of barium chromate soluble in dilute mineral acids but insoluble in water and acetic acid.
CrO + Ba2+ → BaCrO4 ¯
Dichromate ion also gives the same ppt. but due to the formation of strong acid precipitation is partial.
Cr2O+ 2Ba2+ + H2O  2 BaCrO4 ¯ + 2H+
If sodium hydroxide or sodium acetate is added, precipitation becomes quantitative.
(ii) Silver Nitrate Solution: Brownish - red ppt. of silver chromate Ag2CrOwhich is soluble in dil. nitric acid & in ammonia solution, but insoluble in acetic acid.
A reddish brown ppt. of silver dichromate Ag2Cr2O7   is formed with a conc. solution of a dichromate.            
13. Permanganate MnO 
(i) Hydrogen peroxide : It decolourises acidified potassium permanganate solution
                2MnO4+ 5H2O2 + 6H+ ¾¾→ 5O­ + 2Mn2+ + 8H2O.            
(ii) Iron (II) sulphate, in the presence of sulphuric acid, reduces permanganate to
manganese (II). The solution becomes yellow  because of the formation of iron (III) ions
                MnO4- + 5Fe2+ + 8H+ →  5Fe3+ + Mn2+  + 4H2O


TEST FOR CATIONS

GroupGroup reagentIonsColour & ppt.
 Group I dil HCl Pb2+, Hg+, Ag+ PbCl2, Hg2Cl2, AgCl - white
 Group II
 Group II A
 
 Group II B
 
 H2S in dil HCl
 
 Hg2+, Cu2+, Bi3+, Cd2+
 
 As3+, As5+, Sb3+, Sb5+,   Sn2+, Sn4+
 Yellow - CdS,As2S3, As2S5 , SnS2
 Black - HgS, CuS, PbS
 Orange - Sb2S3, Sb2S5
 Brown - Bi2S3 ,SnS
 Group III A NH4OH in presence of   NH4Cl Fe3+, Al3+, Cr3+ Fe(OH)3, Al(OH)3,Cr(OH)Brown      White      Green
 GroupIII B H2S in presence of NH&   NH4Cl or (NH4)2S. Ni2+, Co+2, Mn+2, Zn2+ ZnS  - white or grey,  
 Black - CoS, NiS
 MnS - Buff (light pink)
 Group IV
  
 (NH4)2COin presence of   NH4Cl & NH4OH. Ba+2, Sr2+, Ca+2
 
 BaCO3, SrCO3, CaCO3 - white                                  
 Group V No common group   reagent. Mg+2, Na+, K+, NH4+ ¾


1. Group I (Pb2+, Ag+, Hg+)

  • PbCl2 gives a yellow ppt. with K2CrO4. The ppt. is insoluble in acetic acid but soluble in NaO
  • PbCl2 + 2KI → PbI2  + 2KCl
                                (Yellow)
    PbCl+ 2KI (excess) →  K2[PbI4]
    AgCl is soluble in NH4OH forming a complex while Hg2Clforms a black ppt. with NH4OH.
    AgCl + 2NHOH → Ag(NH3)2Cl + 2H2O
    Hg2Cl2 + 2NH4OH → H2NHgCl + Hg + NH4Cl + 2H2O
                               Amino mercuric Chloride

2. Group II A  (Hg2+, Cu2+, Bi3+, Cd2+)
(i) Hg+2 ions in solution, on addition of SnCl2, give a white precipitate turning black.

2Hg+2 + SnCl→ Sn+4 + Hg2Cl
                                       White
Hg2Cl2 + SnCl2 → SnCl4 + 2Hg
                             Black

(ii) Cu+2 ions in solution give deep blue colour with excess of NH4OH

Cu+2 + 4NH4OH → [Cu(NH3)4 ]+2 + 4H2O
                             Deep blue in colour
Cu+2 ions give chocolate precipitate with K4Fe(CN)6.
2Cu+2 + K4Fe(CN)6 → Cu2[Fe(CN)6] + 4K+

(iii) Bi+3 ions in solution of HCl on addition of water give white cloudy precipitate.

BiCl3 + H2O → BiOCl  + 2HCl
                     White ppt.
When treated with sodium stannite a black ppt. is obtained.
2BiCl3 + 3Na2SnO2  → 2Bi ¯ +  3Na2SnO3 + 6NaCl + 3H2O
                                                black

(iv) Cd+2 ions in solution, with NaOH give a white precipitate.

Cd+2 + 2NaOH →  Cd(OH)2 +  2Na+
                             white
With ammonium hydroxide, Cd2+ ions give a white precipitate which dissolves in excess.  
Cd2+ + 4NH4OH → [Cd(NH3)4](OH)2 + 2H2O

3. Group II B (As3+, As5+, Sb3+, Sb5+, Sn3+, Sn4+)

  • As+3 ions in solution give yellow precipitate with ammonium molybdate and HNOon heating.
    H3AsO4 +12(NH4)2MoO4 +21HNO3 → (NH4)3 AsMo12O40+ 21NH4NO+ 12H2O
                                                                   Yellow ppt.
  • Sn2+ ions in solution as SnCl2 give white ppt. with HgCl2 ,which turns black on standing.
    vii) Sb+3 ions in solution as SbCl3, on addition of water give white precipitate.
    SbCl3 + H2O → SbOCl + 2HCI
                           White

4. Group III A (Al3+, Fe3+, Cr3+)
1. White precipitate of Al(OH)3 is soluble in NaOH

  • Al(OH)3 + NaOH → NaAlO2 + 2H2O

2. Precipitate of Cr(OH)is soluble in NaOH + Br2 water and addition of BaCl2 to this solution gives  yellow precipitate. Fe(OH)3 is insoluble in NaOH
3. Brown precipitate of Fe(OH)3 is dissolved in HCl and addition of KCNS to this solution gives blood red colour.

Also on addition of K4Fe(CN)6 to this solution, a prussian blue colour is obtained.
FeCl+ 3K4Fe(CN)6 → Fe4[Fe(CN)6]3 + 12KCl
                                prussian blue colour

5. Group III B (Ni2+, Co2+, Mn2+, Zn+2)
(i) Ni+2 and Co+2 ions in solution, on addition of KHCO3 and Brwater give apple green colour if Co+2 is present and black precipitate if Ni+2 is present.

CoCl+ 6KHCO3 →K4[Co(CO3)3] + 2KCl + 3CO2­ + 3H2O
2K4[Co(CO3)3] + 2KHCO3 + [O] → 2K3[Co(CO3)3] + 2K2CO3 + H2O
                                                     Apple green colour
NiCl2 + 2KHCO→ NiCO+ 2KCl + H2O + CO2­
2NiCO3 + 4NaOH + [O] → Ni2O3 + 2Na2CO3 + 2H2O
                                    Black ppt.

(ii) Zn+2 ions in solution give white precipitate with NaOH, which dissolve in excess of NaOH.
(iii) Mn+2 ions in solution give pink precipitate with NaOH turning black or brown on heating.

6. Group IV (Ba2+, Sr2+, Ca2+)

  • Ba+2 ions in solution give:

Yellow precipitate with K2CrO4
Ba+2 + K2CrO4 → BaCrO4  + 2K+
                           Yellow

White precipitate with (NH4)2SO4

  • Sr+2 ions give white precipitate with (NH4)2SOand  (NH4)2C2O4
  • Ca+2 ions give white precipitate with (NH4)2 C2O4 only.

7. Group V (NH4+, Na+, K+, Mg+2)
All ammonium salts on heating with alkali say NaOH give a colourless gas with a pungent
smell (NH3)
(A) Gas evolved gives white fumes with HCl
(B) Paper soaked in CuSO4 solution, is turned deep blue by NH3 due to complex formation
(C) With Hg(NO3)2 , a black colour is obtained
Hg2(NO3)2  +  2NH3 → Hg  + Hg(NH2)NO3 ¯ + NH4NO3
                                  black
(D) With Nesslers reagent (alkaline solution of potassium tetraiodomercurate(II) ), a brown ppt. is obtained

  • Potassium salts give yellow ppt. with sodium cobalt nitrite
  • Sodium salts give a heavy white ppt. with potassium dihydrogen antimonate
  • Mg2+ gives white ppt. of magnesium hydroxide with sodium hydroxide
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