Transition Elements Exercise # 4

Exercise # 4 [Subjective Type Questions] 1. Why are Mn2+ compounds more stable than Fe2+ towards oxidation to their +3 state? 2. How is the variability in oxidation states of transition metals different from that of the non transition metals? Illustrate with examples. 3. Which metal in the first series of transition metals exhibits +1 oxidation state most frequently and why? 4. Between Na+ and Ag+, which is stronger Lewis acid and why? 5. Why the highest oxidation state of a metal is exhibited in its oxide or fluoride only? 6. What may be the stable oxidation state of the transition element with the following d electron configurations in the ground state of their atoms: 3d3, 3d5, 3d8 and 3d4? 7. The E (M2+/M) value for copper is positive (+0.34V). What is possibly the Statement-2 for this? 8. Why is the E value for the Mn3+ / Mn2+ couple much more positive than that for Cr3+ /Cr2+ or Fe3+/Fe2+? Explain. 9. Which is a stronger reducing agent Cr2+ or Fe2+ and why? 10. Copper dissolves in dilute nitric acid but not in dilute HCl. Why? 11. Blue colour of CuSO4 solution is discharged slowly when an iron rod is dipped into it. Why? 12. Copper () salts are not known in aqueous solutions. 13. Explain why Cu+ ion is not stable in aqueous solutions? 14. The aqueous solution of FeCl3 is acidic. Why? 15. Ferric iodide is very unstable but ferric chloride is not. 16. Calculate the number of unpaired electrons in the following gaseous ions: Mn3+, Cr3+, V3+ and Ti3+. Which one of these is the most stable in aqueous solution? 17. Mercurous ion is written as Hg22+ whereas cuprous ion is written as Cu+. Explain. 18. Copper sulphate dissolves in NH4OH solution but FeSO4 does not. 19. A hydrated metallic salt (A), light green in colour, on careful heating gives a white anhydrous residue (B), (B) is soluble in water and its aqueous solution gives a dark blue precipitate (C) with potassium hexacyanidoferrate(III). (B) on strong heating gives a brown residue (D) and a mixture of two gases (E) and (F). The gaseous mixture when passed through acidified potassium dichromate, produces green colour solution and when passed through lead acetate solution gave a white precipitate. Out of two gases (E) can act as both reducing as well as oxidising agent. (a) Identify (A), (B), (C), (D), (E) and (F) and give the reactions involved. (b) Explain why salt (A) becomes white on heating. 20. A white substance (A) reacts with dilute H2SO4 to produce a colourless suffocating gas (B) and a colourless solution (C). The reaction of gas (B) with potassium iodate and starch solution produces a blue colour solution. Aqueous solution of (A) gives a white precipitate with BaCl2 solution which is soluble in dilute HCl. Addition of aqueous NH3 or NaOH to (C) produces first a precipitate which dissolves in excess of the respective reagent to produce a clear solution. Similarly addition of excess of potassium ferrocyanide to (C) produces a precipitate (D) which also dissolves in aqueous NaOH giving a clear solution. Identify (A), (B), (C) and (D). Write the equations of the reactions involved. TRANSITION ELEMENTS 21. Write the balanced chemical equation for the following reaction :Nitrogen is obtained in the reaction of aqueous ammonia with potassium permanganate 22. An aqueous solution of inorganic compound (X) gives following reactions. (i) With an aqueous solution of barium chloride a precipitate insoluble in dilute HCl is obtained. (ii) Addition of excess of K gives a brown precipitate which turns white on addition of excess of hyposolution. (iii) With an aqueous solution of K4[Fe(CN)6], a brown coloured precipitate is obtained. Identify (X) and give equations for the reaction for (i), (ii) and (iii) observations. 23. H2S gas is passed through an acidic solution of K2Cr2O7 . The solution turns milky, why? 24. What happens when (i) a small amount of KMnO4 is added to concentrated H2SO4 (ii) an excess amount of KMnO4 is added to concentrated H2SO4 solution. 25. Complete and / balance the following equation : Ag2S + CuCl2 + Hg ..................+..................+ S + 2Ag 26. Which out of the two, La(OH)3 and Lu(OH)3, is more basic and why ? 27. One among the lanthanoides, Ce(III), can be easily oxidized to Ce(IV) (At. No. of Ce = 58). Explain why ? 28. Transition metals forms a large number of interstitial compounds. Explain. 29. Explain the large difference in melting point of Cr(1920ºC) and Zn(420ºC). 30. Although Cu+ does not exist in solution state, but CuCl(s) is formed in presence of Cl– ions in aqueous solution of Cu(s) and Cu2+. 31. Atomic radius in a transition series does not vary much while that of s and p-block does. Why ? 32. The paramagnetic character in 3d transition series increases upto Cr and then decreases. Explain. 33. The ionisation energies of first five members of 3d-series increase with increase in atomic number and then become constant or irregular for next five members. Explain. 34. Pyrolusite on heating with KOH in the presence of air gives a dark green compound (A). The solution of (A) on treatment with H2SO4 gives a purple coloured compound (B), which gives following reactions : (i) KI on reaction with alkaline solution of (B) changes into a compound (C). (ii) The colour of the compound (B) disappears on treatment with the acidic solution of FeSO4 . (iii) With concentrated H2SO4 compound (B) gives (D) which can decompose to yield (E) and oxygen on heating. Identify (A) to (E) and write balanced chemical equations for the formation of (A) and (B) and for the steps (i) to (iii). 35. A black compound (A) in solid state is fused with KOH and KClO3. The aqueous extract of fused mass is green colour solution (B). On passing CO2 gas through it pink colour of (C) is noticed along with some black insoluble mass of (A). The pink coloured solution is decolourised by Fe2+ in acidic medium. What are (A) (B) and (C). 36. (i) An ore (A) on roasting with sodium carbonate and lime in the presence of air gives two compounds, (B) and (C). (ii) The solution of (B) in conc. HCl on treatment with potassium ferrocyanide gives a blue colour or precipitate of compound (D). (iii) The aqueous solution of (C) on treatment with conc. H2SO4 gives a yellow coloured compound (E). (iv) Compound (E) when treated with KCl gives an orange-red compound (F) which is used as an oxidising agent. (v) The solution of (F) on treatment with oxalic acid and then with an excess of potassium oxalate gives blue/violet crystals of compound (G). Identify (A) to (G) and give balanced chemical equations for reactions at steps (i) to (v). 37. Compound (A) is a light green crystalline solid. It gives the following tests. (i) Compound (A) is heated strongly. Gases (B) and (C) with pungent smell come out. A brown residue (D) is left behind. (ii) It dissolves in dilute sulphuric acid. No gas is produced. (iii) A drop of KMnO4 is added to the above solution. The pink colour disappears. (iv) The gas mixture (B and C) is passed into a dichromate solution. The solution turns green. (v) The green solution from step (iv) gives a white precipitate (E) with a solution of barium nitrate. (vi) Residue (D) from step (i) is heated on charcoal in a reducing flame. It gives a magnetic substance. Name the compounds (A), (B), (C), (D) and (E). 38. Cuprous chloride is insoluble in water and dilute HCl but dissolves in concentrated HCl. 39. (i) A blue coloured compound (A) on heating gives two products, (B) and (C). (ii) A metal (D) is deposited on passing hydrogen through heated (B). (iii) The solution of (B) in HCl on treatment with K 4[Fe(CN) 6] gives a chocolate brown coloured precipitate of compound (E). (iv) (C) turns lime water milky which disappears on continuous passage of (C) forming a compound (F). Identify (A) to (F) and give chemical equations for the reactions at steps (i) to (iv). 40. The Cr2O72– ion is a powerful oxidant in acidic medium but is weak oxidant in basic medium. 41. Anhydrous FeCl3 cannot be obtained by heating hydrated ferric chloride. Why ? 42. FeCl3(aq.) gives CO2 with NaHCO3(aq.). Explain. 43. Why is AgNO3 also called lunar caustic ? 44. Hydrated zinc chloride cannot be dehydrated on heating. 45. Compete the following by identifying (A) to (H) 230 º C 800 º C 100 º C (i) CuSO4.5H2O   (B)    (C) + (D).   (A)   Re d heat (ii) AgNO3    (E) + (F) + O2 . 46. Why is AgNO3 kept in brown coloured bottles ?