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1996.ap - U.S National Chemistry Olympiad 1996 National...

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U.S. National Chemistry Olympiad: 1996 National Test Go to Answers 1. What is the formula for the basic anhydride of Ba(OH) 2 ? (A) Ba 2 O (B) BaO (C) BaO 2 (D) Ba 2. Which element exhibits both +1 and +3 oxidation numbers in its compounds? 3. Which element is obtained commercially by electrolysis? 4. A 0.1 M solution of a certain cation will form a precipitate with 0.1 M solutions of all of these anions; OH¯, CO 3 2 ¯, SO 4 2 ¯. Which cation fits this description? (A) Ba 2+ (B) Fe 2+ (C) Mg 2+ (D) Pb 2+ 5. Each of these solutions is added to a mixture of aqueous sodium bromide and chloroform,CHCl 3 . Which one will give a positive test for aqueous bromine when the solutions are vigorously mixed? 6. Oxalic acid dihydrate, H 2 C 2 O 4 . 2 H 2 O(s) is often used as a primary standard to standardize sodium hydroxide solutions. Which of these facts are reasons to choose this substance as a
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primary standard? I. It is diprotic. II. It is a stable compound that can be weighed directly in air. III. It is available in a pure form. (A) III only (B) I and II only (C) II and III only (D) I, II, and III 7. When FeCl 3 is ignited in an atmosphere of pure oxygen,this reaction takes place. 4 FeCl 3 (s) + 3 O 2 (g) ---> 2 Fe 2 O 3 (s) + 6 Cl 2 (g) If 3.0 mol of FeCl 3 are ignited in the presence of 2.0 mol of O 2 gas, how much of which reagent is present in excess and therefore remains unreacted? 8. How many grams of SbF 3 are needed to produce a gram of Freon-12, CCl 2 F 2 , according to the reation represented by this equation? 3 CCl 4 + 2 SbF 3 ---> 3 CCl 2 F 2 + 2 SbCl 3 Substance Molar Mass SbF 3 179 g mol¯ 1 CCl 2 F 2 121 g mol¯ 1 9. A self-contained breathing apparatus uses potassium superoxide, KO 2 , to convert the carbon dioxide and water in exhaled air into oxygen, as shown by the equation. 4 KO 2 (s) + 2 H 2 O(g) + 4 CO 2 (s) ---> 4 KHCO 3 (s) + 3 O 2 (g) How many molecules of oxygen gas will be produced from the 0.0468 g of carbon dioxide that is
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exhaled in a typical breath? 10. Magnetite, Fe 3 O 4 , can be converted into metallic iron by heating with carbon monoxide as represented by this equation. Fe 3 O 4 (s) + 4 CO(g) ---> 3 Fe(s) + 4 CO 2 (g) How many kilograms of Fe 3 O 4 must be processed in this way to obtain 5.00 kg of iron if the process is 85% efficient? Substance Molar Mass Fe 3 O 4 232 g mol¯ 1 (A) 6.92 kg (B) 8.15 kg (C) 20.8 kg (D) 24.4 kg
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