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# Practice1ans - Practice Questions(with answers Quiz#1...

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Practice Questions (with answers) Quiz #1 material (updated 9/25) 1. The typical size of the nucleus and the atom are, respectively: a. 1 nm and 1 mm b. 10 am and 10 fm c. 10 fm and 100 pm d. 1 nm and 1 μ m e. 1 fm and 10 nm 2. The mass density of solid platinum (Pt) is 21.45 g cm -3 . The atomic mass of Pt is 195.09 u. What is the molar density of solid Pt? a. 0.110 mol cm -3 b. 9.10 mol cm -3 c. 3.11 x 10 22 cm -3 d. 4.19 x 10 3 cm -3 e. 1.83 x 10 -25 mol cm -3 3. A certain element has two isotopes, one with mass 78.92 u and 80.92 u, which are found in nature with relative abundances of 50.7% and 49.3%. The standard atomic mass of this element is a. 79.91 u b. 78.92 u c. 79.00 u d. 80.92 u e. None of these

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4. J.J. Thomson determined the charge-to-mass ratio of the electron by: a. Passing cathode rays through crossed magnetic and electric fields b. Firing alpha-particles into a cathode ray tube c. Measuring the rate of fall of charged oil droplets d. Measuring the mass spectrum of Ne e. Detecting the particles produced when electrons strike paraffin 5. Niobium has an atomic mass of 92.91 Da. The mass of 3.011 x 10 23 niobium atoms has a mass of how many grams? a. 13.13 b. 24.24 c. 35.35 d. 46.46 e. 57.57 6. Which of the following nuclear reactions is possible, as written, where α denotes an α -particle? d. All of the above. e. None of the above. 238 234 a. 92 U → 90 Th + α 227 227 b. 89 Ac → 90 Th + α 13 13 c. 7 N → 6 C + α
7. Isotopes of a given element show _________ chemical properties because the chemistry of an atom arises predominantly from __________ a. very different, interactions involving the atom’s electrons. b. very different, interactions involving the atom’s protons. c. very different, the mass of the nucleus. d. nearly identical, interactions involving the atom’s electrons. e. nearly identical, interactions involving the atom’s protons. 8. The typical density (i.e. mass density) of water is ~1 g/cm 3 . Roughly how many molecules of H 2 O are in a spherical raindrop of pure water of radius 1 mm? a. ~10 3 (~1,000) b. ~10 6 (~1,000,000) c. ~10 13 (~10,000,000,000,000) d. ~10 20 (~100,000,000,000,000,000,000) e. ~10 26 (~100,000,000,000,000,000,000,000,000) P.S. Don’t be distracted by the numbers in parentheses; they are only here to impress upon you the magnitude of these number. 9. A chemical element is uniquely identified by its a. mass number b. binding energy c. number of electrons d. atomic number e. mass-to-charge ratio

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10. What must X represent for the following reaction to be possible? a. an α particle b. a positron c. a γ ray d. a positron e. a Helium nucleus 11. Suppose radioactive substance A has a shorter half-life t 1/2 than radioactive substance B. Say that at time t = 0 you have a sample of n moles of A and m moles of B, where m > n . (i.e. there is more B than A). Which of the following is true at the later time t = 2·t 1/2 , where t 1/2 is the half-life of substance A? a. There are still more moles of B than of A in the sample.
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## This note was uploaded on 11/03/2009 for the course CHEM 1403 taught by Professor Leornardfine during the Fall '07 term at Columbia.

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Practice1ans - Practice Questions(with answers Quiz#1...

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