International Junior Science Olympiad Theoretical Sample Question Paper : ijsoweb.org

Organisation : International Junior Science Olympiad
Exam : International Junior Science Olympiad Theoretical
Document Type : Sample Question Paper
Category or Subject : Science

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Junior Science Olympiad Theoretical Sample Question Paper :

Examination Rules :
1. You are NOT allowed to bring any personal items into the examination room, except for personal medicine or approved personal medical equipment.

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2. You must sit at your designated desk.
3. Check the stationeryitems (pen, calculator, and rough book) provided by the organizers.
4. Do NOT start answering the questions before the“START”whistle.
5. You are NOT allowed to leave the examination room during the examination except in an emergency in which case you will be accompanied by a supervisor/volunteer/invigilator.
6. DoNOT disturb other competitors. If you need any assistance you may raise your hand and wait for a supervisor to come.
7. Do NOT discuss the examination questions. You must stay at your desk until the end of the examination time, even if you have finished the exam.

Exam Instructions :
1.After the “START” whistle, you will have 3 hours30 minutes to complete the exam.
2. ONLY use the pen provided by the organizers(not pencil).
3. You have13pages of answer sheets. Raise your hand, if you find any missing sheets.
4. NOW write your name, code, country and signature in your first answer sheet, and your name and code in the next pages of your answer sheets.
5. Read carefully the problems and write the correct answers in the corresponding boxes of theanswer sheet.
6. When units are provided in the answer sheets, you have to write the answers correctly for the units.

Question :
I. Chemical Oxygen Demand (COD) Test
The chemical oxygen demand (COD) test is commonly used for indirectly measuring the amount of organiccompounds in water. Most applications of COD are related to determining the amount of organic pollutants found in surface water (e.g. lakes and rivers) or wastewater, making COD a useful measure of water quality. It is expressed in ppm (parts per million), which indicates the mass of oxygen molecules(in mg) consumed for oxidizing the pollutantsper liter of solution.The basis for the COD test is that nearly all organic compounds can be fully oxidized to CO2 with a strong oxidizing agent under acidic conditions.
The general procedure for the COD test can be described as follows
(A) A solution of K2Cr2O7 (with a known concentration) is added to a solution containing organic pollutants.K2Cr2O7 oxidizes the organic pollutants by the reaction (2).
(B) After completely oxidizing the organic pollutants, the remaining [K2Cr2O7] is determined by titration with Fe2+. In the titration, Fe2+ is oxidized to Fe3+ and Cr2O72- is reduced to Cr3+. This titration will let you know the amount of Cr2O72- used to oxidize the pollutants in the solution.
(C) Using the amount of K2Cr2O7 obtained in step (B), the theoretical amount of oxygen molecules required to oxidize the same amount of the pollutants can be calculated by comparing x and y inequations (1) and (2). This is called COD.

I-1.To determinethe COD from the consumed K2Cr2O7 for oxidizing organic pollutants, the mole ratio between O2 and K2Cr2O7for oxidizing 1 mole of organic pollutant is required. The mole ratio can be determined by comparing x and y inequations (1) and (2) after balancing them. The following procedure is useful.

I-1-1.[0.5 points]Express x in terms of a, b, and c by balancing the equation (1).
I-1-2.[0.5 points]Express z in terms of yby balancing the charge inthe equation (2).
I-1-3.[0.5 points]Express y in terms of a, b, and cby balancing theequation (2).
I-1-4.[0.5 points]Express x in terms of y by comparing your answers.

I-2.To determine the COD of an aqueous solution containing an unknown pollutant, mol of K2Cr2O7 was added to 10.0 mL of the pollutant solution. After the oxidation was completed, mol of Fe2+ was required to titratethe remaining K2Cr2O7.
I-2-1.[1.0point] In the following balanced equation for the reaction between Cr2O72– and Fe2+ in acidic media, what is the coefficient f?
I-2-2.[1.0point] How many moles of K2Cr2O7 were consumed for oxidizing the pollutants in 10.0mL of the polluted solution?
I-2-3. [1.0point]What is the COD of the unknown sample in ppm? The molecularmass of O2 is 32.0 g/mol.

I-3. [2.0points] When 10 mg of each of the following compounds is completely dissolved in 1.0 L of water, which compound produces the highest COD and what is its COD value?(The atomic masses of C, H, and O are 12, 1.0, and 16 g/mol, respectively.)

II. Ski Jumping :
The 2018 Winter Olympics will take place on February 2018, in PyeongChang, Republic of Korea. One of the Winter Olympic competitions is ski jumping, where the skier descends a specially constructed take-off ramp (known as the in-run), then jumps from the launcher(jumping point) with as much speed as he/she can generate, and flies as far as possible down a steeply sloped hill. Figure II-1 shows an outline of a ski jumping hill, divided into four parts: in-run, jump, flight, and landing

II-1. [0.75points] Which of the followingnumbers represented the directions of the gravitational force, normal force, and air resistance, respectively, exerted on the skier during the in-run?

II-2.[1.5points]If the speed of the skier is v at the bottom of the in-run, what is the coefficient (?) of the kinetic friction between the ski and the snow? Express ?in terms ofh, g, s,v, and ?. (Ignore the air resistance and lift.)

II-3.[1.5points]If the launching speed of the skier is v0, what is the flight time (t) from the launcher to the landing point? Express tin terms of k?, g, and v0. (Ignore the air resistance and lift.)

II-4.[1.25points] What is the distance (D) between the launcher and the landing point? Express Din terms of k?, g, and v0. (Ignore the air resistance and lift.)