U.S. National Chemistry Olympiad 1995 National TestGo 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 NH3? (A) AgNO3(B) AlCl3(C) BaCl2(D) MgCl2 2. The members of which pair are most similar in color? 3. Which compound is expected to be the leastsoluble in water? (A) chlorine, Cl2(g), and bromine, Br2(l) (B) silver chloride, AgCl(s), and silver sulfide, Ag2S(s) (C) copper(II) chloride, CuCl2(s), and calcium chloride, CaCl2(s) (D) potassium permanganate, KMnO4(aq), and iodine, I2(g) 4. When a small amount of solid calcium phosphide, Ca3P2, 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?
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% H2SO4by 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(NO3)2.3 H2O equals 241.6 g mol¯1 9. In alkaline solution, chlorine disproportionates to form chloride, Cl¯, and chlorate, ClO3¯, ions. What is the ratio of chloride ions to chlorate ions formed?