CHEM 121a Exam 1 Fall 1997

Transcription

1 SSN CHEM 121a Exam 1 Fall 1997 This exam consists of 20 multiple choice questions (each worth 3 points), and 4 problems (each worth 10 points). There are a total of 100 possible points. Part I. Multiple Choice Questions. Print the correct letter in the space to the left. 1. If there are 2.54 centimeters in one inch, and there are 12 inches in one foot, how many feet are there in 127 centimeters? A ft B. 600 ft C ft D. 323 ft 2. Which of the following is not true of a compound? A. It can be separated into its elements by physical means. B. A compound is a pure substance. C. A sample of a compound has uniform properties throughout. D. A compound may be a liquid, a solid, or a gas. 3. A sample of carbon monoxide, CO, which contains 3.0 x molecules of CO, would have a mass of how many grams? (Atomic masses: C = 12 amu, O = 16 amu; Avogadro s number = 6.0 x ) A. 90 g B. 56 g C. 28 g D. 14 g 4. Bromine exists as a diatomic molecule, Br 2. How many grams are there in 2 moles of bromine molecule? (Atomic mass: Br = 80 amu) A. 80 g B. 40 g C. 160 g D. 320 g 5. In which of the following lists do all of the elements belong to the same group? A. Li, Be, Na, Mg B. Ge, As, Se, Br C. B, Si, As, Te D. S, Te, O, Se 6. Convert 250 K to degrees Fahrenheit. A. 9 F B. 999 F C F D. 23 F 1

2 7. Which of the following mixtures is heterogeneous? A. A solution of table salt, NaCl, in water. B. A mixture of sand and water. C. Bronze, an alloy of copper, tin, and zinc. D. A solution of salt and sugar dissolved in water. 8. In relation to electron, the neutron is: A. About the same mass and of opposite charge. B. About the same mass and with no charge. C. Much lighter and of the same charge. D. Much heavier and with no charge. 9. An atom of an unknown element X has a mass number of 31 and the nucleus contains 15 protons. The element is: A. Gallium, Ga B. Phosphorus, P C. Palladium, Pd D. Sulfur, S 10. How many significant figures should be written in the answer to the following problem: A. 1 B. 2 C. 3 D An ion of an unknown element has an atomic number of 30 and contains 28 electrons. The ion is: A. Ni 2+ B. Si 2 C. Zn 2+ D. P Which of the following units is not an SI unit. A. atmosphere B. second C. meter D. Kelvin 13. What is the volume of a block of manganese which has a density of 7.00 g/cm 3 and a mass of 3.50 g? A cm 3 B cm 3 C cm 3 D L 2

3 14. What is the unit of the answer to the following problem? 12.7 cm/sec x 60 sec/min x 412 min A. cm/min B. sec 1 C. cm D. min/sec/cm 15. In which of the processes is a chemical reaction taking place? A. Dissolving salt in water. B. Melting a nail. C. Burning a newspaper. D. Cutting a lemon. 16. Which statement describes the Rutherford atomic theory more closely? A. Atoms are the smallest particles of elements and are indivisible. B. In an atom, electron and protons are distributed evenly. C. In an atom, most of the mass of the atom is in the nucleus and electrons move around the nucleus at a large distance. D. The electrons can only circulate around the nucleus certain quantized orbits. 17. Consider the following calculation: (6.27 x 10 2 ) x (2.0 x 10 1 ) The answer in the scientific notation is: A B. 1.3 x 10 2 C x 10 3 D How many moles of H 2 O are formed from complete combustion of 2.69 moles of C 2 H 6? A mol B. 2 x 2.69 mol C. 3 x 2.69 mol D. 2.69/2 mol 19. In which set are all of compounds molecular compounds? A. NO, CO 2, CaO B. BF 3, CCl 4, LiF C. NaBr, MgF 2, LiCl D. OF 2, NH 3, NO How many significant figures are in the number ? A. 5 B. 4 C. 7 D. 6 3

4 Part II. Problems. Write all formulas and step-by-step calculations. Partial credit will be given for all work shown. 21. There are two naturally occurring isotopes of lithium. 6 Li (isotopic mass 6.00 amu) and 7 Li (isotopic mass 7.00 amu). The average atomic mass of lithium is 6.93 amu. Calculate the percentage abundance of each isotope. (Hint: To solve this problem, think of one percentage as X and the other as 1.00 X.) 22. Balance the following chemical reactions: A. C 8 H 18 + O 2 CO 2 + H 2 O B. CaSO 3 + HBr CaBr 2 + SO 2 + H 2 O 4

5 23. Calcium reacts with hot water according to the following equation: Ca + 2 H 2 O Ca(OH) 2 + H 2 If excess water is used, how many grams of Ca(OH) 2 will be produced when 27 g of calcium are consumed? (Atomic masses: H = 1.0 amu, C = 12 amu, O = 16 amu, Ca = 40 amu) 24. Give the name or the formula of each compound. A. sodium acetate _ B. magnesium perchlorate _ C. carbon disulfide _ D. aluminum hydroxide _ E. lead (II) phosphite _ F. K 2 Cr 2 O 7 G. NaH 2 PO 4 H. NF 3 I. HNO 3 J. KCN 5