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Chemistry, UNIFIED ACADEMY/XII Foundation, Unit VIII : d- and f- block elements, COHSEM -2005, Q., Describe the general characteristics of transition elements with special references to, 5m, i) variable oxidation states,, iii) catalytic properties,, v) formation of interstitial compounds, ii) complex formations,, iv) formation of coloured ions and, COHSEM - 2006, What is Lanthanide Contraction ? What are its consequences ?, Describe the manufacture of pottasium dichromate from chromate ore. Write the chemical, equations wherever appropriate., 2m, 3m, COHSEM - 2007, O. Write the ground state electronic configuration of Nlobium atom (atomic number = 41). How, many unpaired electrons are present in it., 1 + 1 = 2m, COHSEM -2008, 3m, How will you prepare potassium dichromate from chromite ore ?, COHSEM 2009, 1+ 1 + 1 = 3, Why do transition metals, (i) show variable exidation states,, (iii) exhibit good catalytic properties ?, (ii) form a large number of complex,, COHSEM - 2010, What is the cause of lanthanide contraction and why it is more pronounced than that observed, Q., in an ordinary transition series ?, How does acidified potassium permanganate solution react with (i) iron (ii) ions (iii) iodide ions, 2m, Q., and (iv) oxalic acid., COHSEM -2011, Q. Why is La(OH)3 the most basic while Lu(OH)3is the least in the basic character of the, hydroxides of lanthanides ?, About transition elements, write the following in brief:, (i) metallic character (ii) Oxidation states, Q., 2m, (iii) Formation of coloured ions, 3m, Complete the reaction, 2MnO, (aq)+4H,0,(aq)→ 2Mn2 +8H,0+..., In the reaction :, 1m, heat X + Na,SO, + K,SO, + H,0; X is a reddish-brown gas which gives a, NaCl+ K,Cr,0, + conc.H,SO,, yellow solution on passing through water and a yellow precipitate on treatment the solution, with lead acetate solution. X could be, a) Cl2, b) CrO3, c) H2CRO4, d) CrO2Cl2, COHSEM -2012, Describe the preparation of potassium dichromate from chromite (Fe Cro 04) ore. Write the, chemical equation of the reaction involved. What is the effect of increasing pH of a solution of, potassium dichromate ?, 5m, COHSEM - 2013, Write any two characteristics which can be used to recognise a given element as a -transition, element., 2. Explain, by giving one example each, haw does. KMNO4 oxidize substances in, (i) neutral medium,, 3., (ii) acidic medium and (iii) alkaline medium, COHSEM -2014, What is lanthanide contraction? What causes it? What are important consequences of, lanthanide contraction?, 1+1+33D5, COHSEM -2015, Describe the preparation of potassium dichromate from chromite ore. What is the effect of, increasing pH of o solution of potassium dichromate?, 4+1=5

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UNIFIED ACADEMY/XII Foundation, Chemistry, COHSEM - 2016, (a) Explain the following statements giving reasons:, (i) Transition metals are known to form many interstitial compounds., (ii)Transition metals exhibit variable oxidation states., (iii) The enthalpies of atomisation of transition metals are high., (b) Why transition metals generally form coloured compounds ?, Q., 1 x 3 + 2 = 5, COHSEM -2017, Q., a) Describe the preparation of potassium dichromate from chromite ore., b) Mow does the acidified solution of potassium permanganate react with, i) oxalic acid, ii) Iron (II) ions., 3+2 = 5, COHSEM -2018, Q., The catalyst used in the hydrogenation of oil is, a) Fe, Q., b) Ni, c) Mo, d) Sn, Define transition elements .Zinc, Cadmium and Mercury belong to d-block of the periodic table., But they are not considered as transition elements. Why ?, Q., Write the step-wise process for the preparation of K2Cr,O7 from chromite ore., COHSEM - 2019, Q., What is the most common oxidation state of the Actinoids?, Q., Oxidation I alkaline medium using KmnO4, the oxidation number of manganese changes from, A. +7 to +2, B. +2 to +7, C. +7 to +4, D. +7 to +5, Q., Why is Cuzl2 colourless. Calculate the magnetic moment (spin only) value of the trivalent ion of, element with atomic number 22., COHSEM -2020, Q., Copper (I) has d10 configuration while copper (II) has d° configuration, still copper (II) is more, stable in queons solution that copper (I). Assign reason., The colour of which of the following compounds is NOT due to d-d transition., Q., (a) CoCl2, Q., (b) KMNO4, (c) Cr2(SO4)3, (d) NOSO4, An aqueous solution of gas 'A' gave the following reactions., (i) It decolourised an acidified KMnO4 solution., (ii) On boiling with H2O2 followed by cooling and then adding an aqueous solution of BaCl2, a, white precipitate insoluble in dil.HCl was obtained identify the gas 'A' and give the equation, for step (ii)., Write the stepwise process for the preparation of potassium dichromate from chromite ore., Q., ADDITIONAL QUESTION:, How is potassium permanganate prepared from pyrolusite ore ?, What happend when :, a) Potassium dichronate treated with alkali (eg. KOH), b) Potassium permanganate isheated ?, a) Describe how potassium dichromate is prepared from chromite ore and give the equations, 1., 2., 3., for, the, chemical, reactions involved., b) Write balanced ionic eqations for reacting ions to represent the action of acidified potassium dichromate on :, i) KI solution, c) Write two uses of potassium dichromate., Write steps involved in the preparation of i) Na,Cro, from chromite ore., ii) K,MnO, from pyrolusite ore., ii) FeSO, solution, iii) H,S gas, 4., Assign reasons for the followings:, i) The enthalpies of atomisation of transition elements are high, ii) From element to element the actinoid contraction in greater than the lanthanoid, iii) +2 oxidation state of Mn is quite stable while the same is not true for Fe, iv) The Eo value for the Mn3+ / Mn2 couple is much more positive than that for Cr+/ Cr*, 24 | Page, 5., contraction

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Chemistry, UNIFIED ACADEMY/XII Foundation, v) Scandium (2 = 21) does not exhibit variable oxidation states and vet it is regarded as a transition element., vi) Mn(ii) ion show maximum magnetic character amongst the bivalent ions of first, 6., Why is potassium permanganate kept in dark bottles ?, Calculate the equivalent mass of KMNO, is, transition series., 7., i) neutral medium, ii) Alkaline medium, iii) Acidic medium, 8., Separation of lanthanoids is difficult. Why ?, 9., Configuration of lanthanoids are uncertain. Why?, 10., Explain how the colour of an aqueous solution of K.Cr.O, depends on the pH to the solution., Differentiate between lanthanoids and actinoids., 11.