1995 nat - U.S National Chemistry Olympiad 1995 National...

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U.S. National Chemistry Olympiad 1995 National Test Go to Answers 1. Which 0.1 M solution will form a precipitate with excess 0.1 M KOH but not with excess 0.1 M NH 3 ? (A) AgNO 3 (B) AlCl 3 (C) BaCl 2 (D) MgCl 2 2. The members of which pair are most similar in color? (A) chlorine, Cl 2 (g), and bromine, Br 2 (l) (B) silver chloride, AgCl(s), and silver sulfide, Ag 2 S(s) (C) copper(II) chloride, CuCl 2 (s), and calcium chloride, CaCl 2 (s) (D) potassium permanganate, KMnO 4 (aq), and iodine, I 2 (g) 3. Which compound is expected to be the least soluble in water? 4. When a small amount of solid calcium phosphide, Ca 3 P 2 , is added to water, what are the most likely products? 5. A student plans to calculate the molar mass of an unknown gas from the mass of a measured volume of gas at a known temperature and pressure. To how many significant figures should the student report the molar mass if 175.0 mL of the gas weighs 1.0315 g at a temperature of 22 °C and pressure of 742 mmHg?
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6. The concentration of a colored substance is to be determined by measuring the absorbance of an aqueous solution of it and interpolating from a graph of absorbance versus concentration. Which procedural error will result in a concentration that is too high ? Procedural Mistakes I. rinsing the cuvette with water just before filling it with the unknown solution II. measuring the absorbance of the unknown solution at a wavelength other than its maximum III. using a cuvette for the unknown solution that has a slightly longer path length than you thought it had (A) I only (B) III only (C) I and II only (D) II and III only 7. What is the density (in g mL¯ 1 ) of a 3.60 M aqueous sulfuric acid solution that is 29.0% H 2 SO 4 by mass? 8. Calculate the volume of 0.110 M copper(II) nitrate solution that can be prepared by dissolving 33.29 g of copper(II) nitrate trihydrate in sufficient distilled water. The molar mass of Cu(NO 3 ) 2 . 3 H 2 O equals 241.6 g mol¯ 1 9. In alkaline solution, chlorine disproportionates to form chloride, Cl¯, and chlorate, ClO 3 ¯, ions. What is the ratio of chloride ions to chlorate ions formed?
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