U.S. National Chemistry Olympiad: 1987 National TestGo to answers 1. Assume, as Dalton did, that the atomic weight of oxygen is 7. A sample of 11 g of a uranium oxide contains 10 grams of U. Which of the following is compatible with this data? g. If the international atomic weight scale had defined the mass of a 2-He-4 atom as exactly 4.0, what would be the atomic weight of Li which is 6.941 on the present scale? (A) Uranium oxide is UO and the atomic weight of U is 70. (B) Uranium oxide is U3O8, and the atomic weight of U is 70. (C) Uranium oxide is UO2and the atomic weight of U is 240. (D) Uranium oxide is U2O3and the atomic weight of U is 240. 2. The mass of a 6-C-12 atom is 19.92679 x 10¯24g and that of a 2-He-4 atom is 6.64658 x 10¯24(A) 6.361 (C) 6.936 (B) 6.941 (D) 6.946 3. Separation of the isotopes of uranium requires a physical method rather than a chemical method because 4. The symbol of the element whose nucleus contains 27 neutrons and 22 protons is 5. Analysis of a quantity of it compound shows that it contains 0.110 mol of C, 0.055 mol of N, and 0.165 mol of 0. Its molecular weight is about 270. How many atoms of carbon are there in
the empirical formula for the compound and how many in the molecular formula? 6. A phenomenon that suggests that light is emitted in packets called quanta is 7. The observation that electrons can be diffracted is evidence that electrons (A) have particulate properties. (B) have wave properties. (C) are emitted by atoms. (D) are absorbed by.ions. 8. An electron can move from one orbital of a hydrogen atom to another. In which movement will the photon of highest energy be emitted? 9. The energy in joules of a photon of radiation of wavelength 1.23 x 10¯5m is 10. Which has the greatest ionization energy? 11. Which is the smallest? (A) K
(B) K+(C) Ca (D) Ca2+12. Which bond would be least polar?
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