1991 National - U.S. National Chemistry Olympiad: 1991...

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U.S. National Chemistry Olympiad: 1991 National Test Go to answers 1. What is the mass percent HBr (M = 80.91 mol¯ 1 ) in an 11.4 m solution of HBr in water? (A) 48.0 (B) 25.4 (C) 92.2 (D) 15.3 2. Ethane, C 2 H 6 , burns in oxygen to form carbon dioxide and water. How many grams of oxygen are required to burn 3.01 x 10 23 ethane molecules? (A) 1.04 g (B) 12.0 g (C) 56.0 g (D) 104 g 3. A sample of a pure element that has a mass of 1.00 g also contains 4.39 x 10 21 atoms. What is the element? (A) C (B) Ca (C) Ba (D) Au 4. If the Celsius tempertaure is doubled at constant pressure, what will happen to the volume? (A) It will double. (B) It will remain the same. (C) It will decrease by one-half. (D) Additional information is needed 5. Which is the most metallic element in the fifth period? (A) Y (B) Cd (C) Sn (D) Sb 6. In which set of elements are the atomic radii most nearly the same? (A) Na, Mg, Al
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(B) Cs, Ba, La (C) Na, K, Rb (D) Si, P, S 7. Which compound has the highest percentage of ionic character in its bonding? (A) NaCl (B) MgCl 2 (C) RbF (D) LiI 8. In which gas are the attractive forces between molecules strongest? (A) CH 4 (B) CO 2 (C) H 2 O (D) N 2 9. When comparing diamond and graphite, which is not true? (A) The C orbitals in diamond are sp 3 hybrids and those in graphite are sp 2 hybrids. (B) Graphite forms two-dimensional sheets and diamond forms a three-dimensional covalent network. (C) Graphite is the stable form of carbon at standard temperature and pressure. (D) The bonds in diamond are stronger than those in graphite. 10. Which decrease(s) from Cl 2 to Br 2 to I 2 ? I. Forces between molecules II. Forces within molecules. (A) I only (B) II only (C) Both I and II (D) Neither I nor II 11. When a small amount of heat is added to a pure liquid (a single compound) that is just starting to boil, what is the result? (A) The temperature slightly decreases. (B) The temperature remains the same. (C) The liquid becomes superheated. (D) The temperature increases slightly. 12. Under what conditions is deviation from ideal gas behavior most likely?
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(A) High T and high P. (B) High T and low P. (C) Low T and high P. (D) Low T and low P. 13. For a given mass of an ideal gas, if the pressure of an ideal gas is tripled and its temperature (in kelvins) halved, its volume will be (A) 3/2 of its original volume. (B) 2/3 of its original volume. (C) 1/6 of its original volume. (D) 6 times its original volume. 14. What is the most dense element listed below? (A) Ba (B) Pb (C) Os (D) Rn 15. What is the volume of CO 2 measured at 25 °C and 1.2 atm when 25 g of CaCO 3 is totally decomposed? CaCO 3 -----> CaO + CO 2 (A) 10.2 L (B) 2.6 L (C) 15.3 L (D) 5.1 L 16. If 500 mL of methane, CH 4 , effuses through a small hole in 48 s, how much time is required for the same volume of helium to pass through the hole? (A) 12 s (B) 24 s (C) 96 s (D) 192 s 17. When the stocpcock is opened and equilibrium is established between the two bulbs, what is the total pressure in the system?
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(A) 1.4 atm (B) 1.8 atm (C) 2.0 atm (D) 3.6 atm 18. Which set gives the correct formulas of the most stable forms of nitrogen, phosphorous, and arsenic at room temperature and pressure?
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This note was uploaded on 11/09/2011 for the course CHEM 111 taught by Professor Rogers during the Fall '08 term at Thomas Edison State.

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1991 National - U.S. National Chemistry Olympiad: 1991...

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