1990 - U.S. National Chemistry Olympiad: 1990 National Test...

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U.S. National Chemistry Olympiad: 1990 National Test Go to the answers 1. In moving from left to right across a period in the periodic table of the elements (A) ionization energy decreases (B) atomic radius decreases (C) electronegativity decreases (D) electron affinity decreases 2. Which transition is associated with the largest change in energy in the hydrogen atom? (A) n = 5 to n = 3 (B) n = 2 to n = 1 (C) n = 3 to n = 2 (D) n = 4 to n = 2 3. In which pair are the elements most similar in their chemical properties? (A) B and N (B) Li and Fr (C) Mg and Al (D) S and Cl 4. A 4.0 g sample of impure Ca(NO 3 ) 2 was found to contain 0.85 g of calcium. What percentage of Ca(NO 3 ) 2 was in the original sample? (molar mass of Ca(NO 3 ) 2 = 164.1 g mol¯ 1 ) (A) 13 % (B) 36 % (C) 64 % (D) 87 % 5. Aluminum hydroxide, Al(OH) 3 , is insoluble in water, but dissolves readily in both acidic and basic solutions. Such behavior is characteristic of (A) polyprotic behavior. (B) hydrophilic behavior. (C) amphoteric behavior. (D) a buffer. 6. The freezing point of a 1.00 m aqueous solution of HF is found to be -1.91 °C. The freezing point constant is water, k f , is 1.86 K 1 . What is the percent of dissociation of HF at this concentration?
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(A) 2.7 % (B) 5.2 % (C) 10 % (D) 30 % 7. Enthapies of formation cannot be measured for many compounds directly, and must be calculated from combustion data. Given the following data, calculate the heat of formation of glucose, C 6 H 12 O 6 . C (graphite) + O 2 (g) --> CO 2 (g) H = -394 kJ mol¯ 1 H 2 (g) + 1/2 O 2 (g) --> H 2 O (l) H = -286 kJ mol¯ 1 C 6 H 12 O 6 (s) + 6 O 2 (g) --> 6 CO 2 (g) + 6 H 2 O (l) H = -2808 kJ mol¯ 1 (A) -1272 kJ mol¯ 1 (B) +1272 kJ mol¯ 1 (C) +2128 kJ mol¯ 1 (D) -3488 kJ mol¯ 1 8. If the enthalpy of fusion of iodine is +15.5 kJ mol¯ 1 , and the enthalpy of sublimaiton of iodine is +57.3 kJ mol¯ 1 , what is the enthalpy of vaporization of iodine? (A) -41.8 kJ mol¯ 1 (B) +41.8 kJ mol¯ 1 (C) -72.8 kJ mol¯ 1 (D) +72.8 kJ mol¯ 1 9. If, for N 2 , H vap = 5.58 kJ mol¯ 1 and S vap = 72.1 J mol¯ 1 1 , at low temperatures, in what phase will N 2 be at -165 °C? (A) gas (B) liquid (C) solid (D) at the liquid/gas phase boundary 10. Which of the following molecules contains a central atom which is sp 2 hybridized? (A) H 2 SO 4 (B) H 2 CO 3 (C) ICl 2 (D) H 3 CCH 3 11. Which of the following molecules has at least one non-bonding pair of electrons on the central atom?
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(A) CHCl 3 (B) HCN (C) H 2 CO (D) O 3 12. Which of the following statements about ionic compounds is false? (A) Ionic compounds are hard, brittle solids with high melting points. (B) Some compounds which exhibit primarily ionic bonding in the solid phase can form covalent bonds in the gas phase. (C) The lattice energy is the quantity of energy required for 1 mol of a solid ionic substance to be separated completely into gaseous ions well removed from one another. (D) In general the lattice energy increases as the charge on the anion and cation increase and increases as the size of the anion and cation decrease.
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1990 - U.S. National Chemistry Olympiad: 1990 National Test...

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