Qualitative Analysis (Cations) Exercise -3

Qualitative Analysis (Cations) * Marked Questions may have more than one correct option. PART - I : (ADVANCED) / PROBLEMS (PREVIOUS YEARS) 1. A metal nitrate reacts with KI to give a black precipitate which on addition of excess of KI is converted into orange colour solution. The cation of the metal nitrate is : (A) Hg2+ (B) Bi3+ (C) Pb2+ (D) Cu+ 2. In the given reaction sequence, Identify (A) and (B). − SCN → Fe3+ ⎯⎯⎯ (Excess) (a) (b) A Blood red − F (excess) ⎯⎯⎯⎯⎯ → colourless(B) Write the IUPAC name of (A) and (B). Find out the spin only magnetic moment of B. 3. A white precipitate is obtained when a solution is diluted with H 2O and boiled. On addition of excess NH4Cl/NH4OH, the volume of precipitate decreases leaving behind a white gelatinous precipitate. Identify the precipitate which dissolves in ammonia solution or NH 4Cl. (A) Al(OH)3 (B) Zn(OH)2 (C) Mg(OH)2 (D) Ca(OH)2 4. In blue solution of copper sulphate excess of KCN is added then solution becomes colourless due to the formation of : (A) [Cu(CN)4]2– (B) Cu2+ get reduced to form [Cu(CN)4]3– (C) Cu(CN)2 (D) CuCN 5. MgSO4 + NH4OH + Na2HPO4 ⎯⎯→ white crystalline precipitate. The formula of crystalline precipitate is: (A) MgCl2. MgSO4 (B) MgSO4 (C) Mg(NH4)PO4 (D) Mg(PO4)2 6. A solution of a metal ion when treated with K gives a red precipitate which dissolves in excess K to give a colourless solution. Moreover, the solution of metal ion on treatment with a solution of cobalt(II) thiocyanate gives rise to a deep blue crystalline precipitate. The metal ion is : (A) Pb2+ (B) Hg2+ (C) Cu2+ (D) Co2+ 7.* A solution of colourless salt H on boiling with excess NaOH produces a non-flammable gas. The gas evolution ceases after some time. On addition of Zn dust to the same solution, the gas evolution restarts. The colourless salt(s) H is (are) : (A) NH4NO3 (B) NH4NO2 (C) NH4Cl (D) (NH4)2SO4 Paragraph for Question Nos. 8 to 10 p-Amino-N, N-dimethylaniline is added to a strongly acidic solution of X. The resulting solution is treated with a few drops of aqueous solution of Y to yield blue coloration due to the formation of methylene blue. Treatment of the aqueous solution of Y with the reagent potassium hexacyanoferrate(II) leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly, treatment of the solution of Y with the solution of potassium hexacyanoferrate(III) leads to a brown coloration due to the formation of Z. 8. 9. 10. The compound X is : (A) NaNO3 (B) NaCl (C) Na2SO4 (D) Na2S The compound Y is : (A) MgCl2 (B) FeCl2 (C) FeCl3 (D) ZnCl2 The compound Z is : (A) Mg2[Fe(CN)6] (B) Fe[Fe(CN)6] (C) Fe4[Fe(CN)6]3 (D) K2Zn3[Fe(CN)6]2 Qualitative Analysis (Cations) Paragraph for Question Nos. 11 to 13 When a metal rod M is dipped into an aqueous colourless concentrated solution of compound N the solution turns light blue. Addition of aqueous NaCl to the blue solution gives a white precipitate O. Addition of aqueous NH3 dissolves O and gives an intense blue solution. 11. 12. 13. 14. The metal rod M is : (A) Fe (B) Cu (C) Ni (D) Co The compound N is : (A) AgNO3 (B) Zn(NO3)2 (C) Al(NO3)3 (D) Pb(NO3)2 The final solution contains (A) [Pb(NH3)4]2+ and [CoCl4]2– (C) [Ag(NH3)2]+ and [Cu(NH3)4]2+ Passing H2S gas into a mixture of Mn2+, Ni2+, Cu2+ and Hg2+ ions in an acidified aqueous solution precipitates: (A) CuS and HgS 15.* 16.* (B) [Al(NH3)4]3+ and [Cu(NH3)4]2+ (D) [Ag(NH3)2]+ and [Ni(NH3)6]2+ (B) MnS and CuS (C) MnS and NiS The equilibrium, 2CuI Cu0 + CuII in aqueous medium at 25° C shifts towards the left in the presence of : (A) NO3– (B) Cl– (C) SCN– (D) NiS and HgS (D) CN– For the given aqueous reaction which of the statement(s) is (are) true ? (A) The first reaction is a redox reaction (B) White precipitate is Zn3[Fe(CN)6]2 (C) Addition of filtrate to starch solution gives blue colour. (D) White precipitate is soluble in NaOH solution 17. Upon treatment with ammoniacal H2S, the metal ion that precipitates as a sulphide is : (A) Fe(III) (B) Al (III) (C) Mg(II) (D) Zn(II) Paragraph for Question 18 and 19 An aqueous solution of a mixture of two inorganic salts, when treated with dilute HCl, gave a precipitate (P) and a filtrate (Q). The precipitate P was found to dissolve in hot water. The filtrate (Q) remained unchanged, when treated with H2S in a dilute mineral acid medium. However, it gave a precipitate (R) with H2S in an ammoniacal medium. The precipitate R gave a coloured solution (S), when treated with H2O2 in an aqueous NaOH medium. 18. 19. 20. The precipitate P contains (A) Pb2+ (B) Hg22+ (C) Ag+ (D) Hg2+ The coloured solution S contains (A) Fe2(SO4)3 (B) CuSO4 (C) ZnSO4 (D) Na2CrO4 Among PbS, CuS, HgS, MnS, Ag2S, NiS, CoS, Bi2S3 and SnS2, the total number of BLACK coloured sulphides is : Qualitative Analysis (Cations) 21.* The pair(s) of ions where BOTH the ions are precipitated upon passing H 2S gas in presence of dilute HCl, is(are) (A) Ba2+, Zn2+ (B) Bi3+, Fe3+ (C) Cu2+, Pb2+ (D) Hg2+, Bi3+ 22. In the following reaction sequence in aqueous solution, the species X, Y and Z, respectively, are 2– S2 O3 + Ag X Clear solution Ag (A) [Ag(S2O3)2]3–, Ag2S2O3, Ag2S (C) [Ag(SO3)2]3–, Ag2S2O3, Ag 23.* + Y with time white precipitate Y black precipitate (B) [Ag(S2O3)3]5–, Ag2SO3,Ag2S (D) [Ag(SO3)3]3–, Ag2SO4,Ags The correct option(s) to distinguish nitrate salts of Mn2+ and Cu2+ taken separately is (are) (A) Mn2+ show the characteristic green colour in the flame test (B) Only Cu2+ show the formation of precipitate by passing H2S in acidic medium (C) Only Mn2+ show the formation of precipitate by passing H2S in faintly basic medium (D) Cu2+/Cu has higher reduction potential than Mn2+/Mn (measured under similar conditions) PART - II : (MAIN) / PROBLEMS (PREVIOUS YEARS) (MAIN) OFFLINE PROBLEMS 1. Which one of the following statement is correct ? (1) From a mixed precipitate of AgCl and AgI, ammonia solution dissolves only AgCl. (2) Ferric ions gave a deep green precipitate on adding potassium ferrocyanide solution. (3) On boiling a solution having K+, Ca2+ and HCO3– ions we get a precipitate of K2Ca(CO3)2. (4) Manganese salts give a violet borax bead test in the reducing flame . 2. A red solid is insoluble in water. However it becomes soluble if some K is added to water. Heating the red solid in a test tube results in liberation of some violet coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid is : (1) (NH4)2 Cr2O7 (2) Hg2 (3) HgO (4) Pb3O4. 3. Which of the following compounds is not colored yellow ? (1) Zn2[Fe(CN)6] (2) K3[Co(NO2)6] (3) (NH4)3[As(Mo3O10)4] (4) BaCrO4 4. Sodium salt of an organic acid ‘X’ produces effervescence with conc. H 2SO4. ‘X’ reacts with the acidified aqueous CaCl2 solution to give a white precipitate which decolourises acidic solution of KMnO4. ‘X’ is: (1) HCOONa (2) CH3COONa (3) Na2C2O4 (4) C6H5COONa (MAIN) ONLINE PROBLEMS 1. The cation that will not be precipitated by H2S in the presence of dil HCl is: (1) Pb2+ 2. (2) As3+ (3) Co2+ (4) Cu2+ An aqueous solution of a salt X turns blood red on treatment with SCN – and blue on treatment with K4[Fe(CN)6]. X also gives a positive chromyl chloride test. The salt X is : (1) CuCl2 (2) Cu(NO3)2 (3) FeCl3 (4) Fe(NO3)3 Qualitative Analysis (Cations) 3. When concentrated HCl is added to an aqueous solution of CoCl 2, its colour changes from reddish pink to deep blue. Which complex ion gives blue colour in this reaction? (1) [CoCl4]2– 4. (2) [CoCl6]3– (3) [CoCl6]4– (4) [Co(H2O)6]2+ A pink coloured salt turns blue on heating. The presence of which cation is most likely ? (1) Co2+ (2) Cu2+ (3) Zn2+ (4) Fe2+ 5. A solution containing a group-IV cation gives a precipitate on passing H 2S. A solution of this precipitate in dil. HCl produces a white precipitate with NaOH solution and bluish-white precipitate with basic potassium ferrocyanide. The cation is : (1) Mn2+ (2) Zn2+ (3) Co2+ (4) Ni2+ 6. The incorrect statement is : (1) Cu2+ ion gives chocolate coloured precipitate with potassium ferrocyanide solution. (2) Cu2+ and Ni2+ ions give black precipitate with H2S in presence of HCl solution. (3) Ferric ion gives blood red colour with potassium thiocyanate. (4) Cu2+ salts give red coloured borax bead test in reducing flame. EXERCISE - 3 PART - I 1. (B) 2. (a) (A) = Pentaaquathiocyanato-S-iron(III) ; (B) = Hexafluoridoferrate(III) (b) 5.93 B.M. 3. (B) 4. (B) 5. (C) 6. (B) 7.* (AB) 8. (D) 9. (C) 10. (B) 11. (B) 12. (A) 13. (C) 14. (A) 15.* (BCD) 16.* (ACD) 17. (D) 18. (A) 19. (D) 20. 7 21.* (CD) 22. (A) 23.* (BD) 4. (3) 4. (1) 5. (2) PART - II (MAIN) OFFLINE PROBLEMS 1. (1) 2. (2) 3. (1) (MAIN) ONLINE PROBLEMS 1. (3) 6. (2) 2. (3) 3. (1)