olympiads.hbcse.tifr.res.in Indian National Chemistry Olympiad INChO 2016 : Homi Bhabha Centre For Science Education
Name of the Centre : Homi Bhabha Centre For Science Education
Name Of The Exam : Indian National Chemistry Olympiad INChO 2016
Name Of The Subject : Chemistry
Document type : Previous Question Papers
Year : 2016
Website : http://olympiads.hbcse.tifr.res.in/how-to-prepare/past-papers/
Download Model/Sample Question Paper :
INChO 2016 : https://www.pdfquestion.in/uploads/13135-INChO-2016.pdf
INChO 2015 : https://www.pdfquestion.in/uploads/13135-incho2015.pdf
INChO 2014 : https://www.pdfquestion.in/uploads/13135-incho2014.pdf
INChO 2013 : https://www.pdfquestion.in/uploads/13135-incho2013.pdf
INChO 2012 : https://www.pdfquestion.in/uploads/13135-incho2012.pdf
Indian National Chemistry Olympiad :
Theory (3 hours) :
Instructions for students :
** Write your Name and Roll No. at the top of the first pages of all problems.
** This examination paper consists of 28 pages of problems including answer boxes.
Related : Homi Bhabha Centre For Science Education Indian National Biology Olympiad INBO 2016 : www.pdfquestion.in/13129.html
** Kindly check that the booklet has all the pages.
** Total marks for INChO 2016 paper are 102.
** You have 3 hours to complete all the problems.
** Blank space for rough work has been provided at the end of the paper.
** Use only a pen to write the answers in the answer boxes. Anything written by 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.
** You must show the main steps in the calculations.
** Use only a non-programmable scientific calculator.
** For objective type question, mark X in the correct box. Some of the objective questions may have more than one correct answer.
** 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.
Problem 1 20 Marks :
Sulphate dynamics in Wastewaters :
Wastewaters are one of the highly complex chemical systems in our environment. Understanding these complex chemical reactions is important for safe management of wastewater systems. Here we look at some of the chemical dynamics of sulphate ions in wastewaters. Under scarcity of stronger oxidizers such as O2 and NO3 ?, SO4 2? ions can act as oxidizing agents for organic matter in wastewater aiding its decomposition. Sulphate reduction is often facilitated by sulphate-reducing bacteria (SRB), which are usually present in sewage and thrive in an anaerobic (low oxygen)environment. Sulphate reduction can eventually lead to production of toxic H2S gas. The overall redox reaction can be represented by the equation
For all parts in this problem, take temperature of the system to be 298 K. :
1.1 Determine the change in standard Gibbs free energy, ?G°, for reaction (2) in kJ.
1.2 Write an expression for equilibrium constant, K, for reaction (2) in terms of molar concentrations of the relevant chemical species.
1.3 Calculate the value of K for reaction (2).
1.4 A sewage entering a septic tank has [SO4 = 0.5 mM and pH = 7.0. Assuming (2) to be the predominant redox reaction in the sewage, determine the concentration of dissolved H2S in it when the system reaches equilibrium. (For H2S, pKa1 = 7.0 and pKa2 = 11.96). Assume that
(a) H2S and CO2 gases produced remain in the solution phase.
(b) the carbonic acid produced here doesn’t undergo dissociation.
(c) the sewage acts as buffer
1.5 Following graphs show temperature dependence of solubility of the three gases in water, which includes the gas in dissolved form as well as its reaction products with water.
i) Label the boxes in each graph with appropriate gas.
ii) Which of the three gases will escape from sewage the fastest?
Indian National Chemistry Olympiad 2015 :
Problem 1 : 17 marks
Oxides of nitrogen :
Nitrogen is one of the most important elements on earth. It forms several oxides including nitric oxide and nitrogen dioxide. Nitric oxide is an air pollutant produced in the combustion processes in automobile engines and power plants.
1.1 Write the Lewis dot structures of nitric oxide and nitrogen dioxide.
In the chemical industry, nitric oxide is an important intermediate produced by oxidation of ammonia by oxygen. This is the first step in the Ostwald’s process of the manufacture of nitric acid.
1.2 Write the balanced equation for the oxidation of ammonia to nitric oxide by oxygen.
1.3 In a closed vessel, at 700 K and a pressure of 1 atm, 100 kmols of ammonia are mixed with 20% excess of air than that required for complete combustion of ammonia. (air ontains 80% nitrogen and 20% oxygen on volume basis) i) Calculate the initial number of moles of oxygen and nitrogen present in the system
ii) At equilibrium, 70% yield of nitric oxide was obtained in the closed vessel. Calculate the mole percent of ammonia and water present in the mixture at equilibrium.
Some equilibrium of nitrogen oxides, which can be exploited commercially are shown below. (From Questions 1.4 to 1.8, you need to refer to these equations.)
A) N2 (g) + O2(g) – 2NO(g)
B) 2NO(g) + O2(g) – 2 NO2(g)
1.4 Using the following data, calculate the standard free energy change in kJ for reaction A. The temperature is 298.15 K.
1.5 At 298.15 K, the ?Go of formation for N2O4(g), and NO2(g) are 98.28 kJ mol?1 and 51.84 kJ mol-1 respectively. Starting with 1 mole of N2O4(g) at 1.0 atm and 298.15 K, calculate % of N2O4 decomposed if the total pressure is kept constant at 1.0 atm and the temperature maintained at 298.15 K.