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? 3. In which pair are the elements most similar in their chemical properties? 4. A 4.0 g sample of impure Ca(NO3)2was found to contain 0.85 g of calcium. What percentage of Ca(NO3)2was in the original sample? (molar mass of Ca(NO3)2= 164.1 g mol¯1) 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 maqueous solution of HF is found to be -1.91 °C. The freezing point constant is water, kf, is 1.86 K m¯1. What is the percent of dissociation of HF at this concentration?
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? 9. If, for N2, Hvap= 5.58 kJ mol¯1and Svap= 72.1 J mol¯1K¯1, at low temperatures, in what phase will N2be at -165 °C? 10. Which of the following molecules contains a central atom which is sp2hybridized? (A) H2SO4(B) H2CO3(C) ICl2(D) H3CCH3 11. Which of the following molecules has at least one non-bonding pair of electrons on the central atom?
12. Which of the following statements about ionic compounds is false?
You've reached the end of your free preview.
Want to read all 14 pages?