Incho 2011 Chemistry Question Paper From India Indian National Chemistry Olympiad

Indian National Chemistry Olympiad Theory 2011 Instructions for students • Write your name and roll no. at the top of the first pages of all problems. • This examination paper consists of 32 pages of problems including answer boxes. • Total marks of INChO 2011 paper is 102 and the scores will be normalized to 100 marks. ** • You have 3 hours to complete all the problems. • Request the supervisor to provide you with rough sheets for rough work. • Use only a pen to write the answers in the answer boxes. Anything written by a pencil will not be considered for assessment. • All answers must be written in the appropriate boxes. Anything written elsewhere will not be considered for assessment. • For calculations, you must show the main steps. • Use only a non-programmable scientific calculator. • For objective type questions: Mark X in the correct box. Some of the objective questions may have more than one correct choice. • Values of fundamental constants required for calculations are provided on page 2. • A copy of the Periodic Table of the Elements is provided at the end of the paper. • Do not leave the examination room until you are directed to do so. • The question paper will be uploaded on the HBCSE website by 1st February 2011. © Homi Bhabha Centre For Science Education Tata Institute of Fundamental Research V.N. Purav Marg, Mankhurd, Mumbai 400 088. HBCSE, 29th January 2011 1 Indian National Chemistry Olympiad Theory 2011 Fundamental Constants Avogadro constant NA = 6.022 x 1023 mol–1 Electronic charge e = 1.602 x 10–19 C Molar gas constant R = 8.314 J K–1mol–1 = 8.314 K Pa.dm3 K–1mol–1 = 0.082 L.atm K–1mol–1 1 atomic mass unit (1u) = 931.5 MeV/c2 1 eV = 1.602 x 10–19 J Rydberg constant RH = 2.179 x 10–18 J Mass of electron me = 9.109 x 10–31 kg Planck’s constant h = 6.625 x 10–34 Js Speed of light c = 2.998 x 108 ms−1 Acceleration due to gravity g = 9.8 ms−2 Density of mercury = 13.6 x 103 kg m−3 Faradays Constant = 96500 C HBCSE, 29th January 2011 2 Indian National Chemistry Olympiad Name of Student Theory 2011 Roll No. Problem 1 17 Marks Chromium, the first element in Group 6 is a steely-gray, lustrous, hard metal. The name of this element is derived from the Greek word chrōma meaning colour because many of its compounds are intensely coloured. This element was discovered by Louis Nicolas Vauquelin in the mineral crocoite (lead chromate). The diagram indicating the standard potential values connecting species of an element present in different oxidation states is known as Latimer diagram. In such a diagram, the most oxidized form of an element is represented at the extreme left, and in successive species the oxidation number of the element goes on decreasing from left to right. The numerical values of E° (volt) are written above the lines joining the successive species. Latimer diagram for chromium is presented below. (All data refer to pH = 1) 0.293 + 0.55 + 2.1 X Y - 0.912 → Cr(V) → Cr(IV) → Cr(III) → Cr(II) → Cr Cr O2 − (VI) 2 7 orange red green violet blue −0.744 1.1 Calculate the values of X and Y in the above Latimer diagram. (1.5 marks) 1.2 With appropriate calculations, show Cr (IV