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9 Introductory Chemistry I Chemistry 1111 September 17, 2009 Hour Examination I Name There is a Periodic Table and a summary of solubility rules attached to the end of this examination. You may use a non-programmed calculator while taking the examination, which will require approximately 75 minutes. You may leave quietly when you have completed the examination. The answers to the multiple-choice questions (1-24) are to be recorded on the computer form and count four points each; the responses to questions are to be written on the test. FYI: Avogadro's number = 6.02 x Imagine two candles burning in a trough of water. If they are covered with an inverted glass jar (as we did with one candle in class), they will eventually be extinguished. One would expect: a. The water level to rise slowly and steadily as the candles consume the oxygen in the air, just as with one candle b. The water level to rise slowly and steadily as the carbon dioxide produced by the candles dissolves in the water, just as with one candle. c. The water level in the jar to subside at first, and then rise quickly when the candles go out. d. The water level to rise twice as high as it did with one candle, because two candles would consume twice as much oxygen. e. None of the above. 2. Which of the following represents the group of measurements in order from smallest to largest? a. 1 nl, 2 ml, 3 dl, 4 kl b. 1 dg, 2 mg, 3 cg, 4 pg c. 1 Mg, 2 dg, 3 cg, 4 mg d. 1 ks, 2 ms, 3 Ms, 4 ns e. 1 cm, 2 dm, 3 km, 4 mm 3. What is the average mass (in grams) of one atom of mercury? a x b x c x d e

4. Analysis of a 6.604 gram sample of a substance disclosed that it contained 2.64 grams of carbon, 0.444 grams of hydrogen, and 3.52 grams of oxygen. What is its empirical formula? a. C 3 H 4 O 4 b.

10 4. Analysis of a gram sample of a substance disclosed that it contained 2.64 grams of carbon, grams of hydrogen, and 3.52 grams of oxygen. What is its empirical formula? a. C 3 H 4 O 4 b. C 3 H 4 O 3 c. C 3 H 4 O 2 d. CH 2 O e. CHO 5. Methane and oxygen react to form carbon dioxide and water. What mass of water is formed if 0.80 g of methane reacts with 3.2 g of oxygen to produce 2.2 g of carbon dioxide? The balanced chemical equation is: CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g) a. 1.8 g b. 2.2 g c. 3.7 g d. 4.0 g e. None of the above 6. In the drawing below, shaded spheres represent cations and unshaded spheres represent anions. Which drawing represents the ionic compound Mg3(PO4)2? a. drawing (a) b. drawing (b) c. drawing (c) d. drawing (d) 7. If the percent yield for the following reaction is 65.0%, how many grams of KClO3 are needed to produce 42.0 g of O 2? a. 107 g b. 165 g c. 214 g d. 241 g e. 371 g 2 KClO3(s) = 2 KCl(s) + 3 O2(g) 2

11 8. The freezing point of methane is -298 F and the boiling point is -263 F. The temperature of the surface of Titan, a moon of Saturn, is 93 K. If methane exists on Titan, it is: a. a plasma b. a solid c. a liquid d. a gas e. a mixture of solid and liquid 9. Very careful measurements made with an analytical balance determined the mass of a small crystal to be grams. How many significant figures are expressed in this quantity? a. 1 b. 2 c. 3 d. 4 e Which of the following is part of Dalton's atomic theory? a. atoms break down during radioactive decay b. atoms are rearranged but not changed during a chemical reaction c. atoms contain protons, neutrons, and electrons d. isotopes of the same element have different masses e. the periodic table is based on the masses of elements 11. Which of the following would be another isotope of an atom with atomic number 20 and mass number 42? An atom with: a. an atomic number of 21 and a mass number of 42 b. 20 protons and a mass number of 40 c. 20 protons and 22 neutrons d. 22 protons and 20 neutrons e. 21 protons and 21 neutrons 12. What is the mass in grams of mole of -fructose, C 6 H ? a x g b g c g d g e. 180 g 3

12 13. Dinitrogen monoxide (also known as nitrous oxide, laughing gas, or N 2 O) decomposes to form nitrogen gas and oxygen gas. How many grams of oxygen are formed when 5.00 g of dinitrogen monoxide decomposes? a g b g c g d g e. None of the above 14. A 5.0 g sample of pure strontium arsenate is 38.68% strontium by mass. What is the percent strontium by mass in a sample of pure strontium arsenate with a mass of 10.0 g? a % b % c % d % e. None of the above 15. Two compounds that could be used to illustrate the law of multiple proportions are: a. H 2 O and D 2 O b. S 4 and S 6 c. CH 4 and SiH 4 d. NH 3 and N 2 H 4 e. Diamond and graphite 16. There are two known isotopes of Surprisium, the element of surprise. 280 Su has a natural abundance of 75%. If the atomic mass in the periodic table is then the mass of the second isotope is a. 275 amu b. 277 amu c. 278 amu d. 279 amu e. 281 amu 17. The mixing of which pair of reactants will result in a precipitation reaction? a. Cu(NO 3 ) 2 (aq) + Na 2 CO3(aq) b. K 2 SO 4 (aq) + Cu(NO 3 ) 2 (aq) c. NaClO 4 (aq) + (NH4) 2 S(aq) d. NH 4 Br(aq) + NaI(aq) e. CaCl 2 (aq) + NaOH(aq) 4

13 18. How many chlorine atoms are present in 43.6 g of FeCl 3? a x b x c x d e A sample of glucose, C 6 H 12 O 6, contains 4.0 x atoms of carbon. How many atoms of hydrogen and how many molecules of glucose does it contain? a. 8.0 x atoms of H; 8.0 x molecules of glucose b. 8.0 x atoms of H; 4.0 x molecules of glucose c. 4.0 x atoms of H; 4.0 x molecules of glucose d. 8.0 x atoms of H; 6.7 x molecules of glucose e. 8.0 x atoms of H; 2.4 x molecules of glucose 20. Which of the following has the smallest mass? a molecules of I 2 b g of Cl 2 c mol of F 2 d kg of Br 2 e mol At If unshaded spheres represent nitrogen atoms and shaded spheres represent oxygen atoms, which box below represents reactants and which represents products for the reaction 2 N2O(g) 2 N2(g) + O2(g)? a. box (a) reactants and box (c) products b. box (a) reactants and box (d) products c. box (b) reactants and box (c) products d. box (b) reactants and box (d) products e. no combination of boxes can represent reactants and products 22. The balanced net ionic equation for the reaction of H 2 SO 4 (aq) with Ba(OH) 2 (aq) is: a. H 2 SO 4 (aq) + Ba(OH) 2 (aq) BaSO 4 (s) + 2 H 2 O(l) b. 2 H + (aq) + SO 4 2- (aq) + Ba 2+ (aq) + 2 OH - (aq) BaSO 4 (s) + 2 H 2 O(l) c. H + (aq) + OH - (aq) H 2 O(l) d. Ba 2+( aq) + SO 4 2- (aq) BaSO 4 (s) 5

14 23. Which of the species below has 28 protons and 26 electrons? a. 2 Fe 54 b. 26 Fe c. 2 Ni 54 d. 28 Ni e Fe 24. Instead of using water, a student submerged an irregularly-shaped piece of metal into a graduated cylinder that contained ethanol, whose density is g/ml. The initial volume of the liquid was 23.4 ml, but the meniscus rose to 41.8 ml when the metal was added. If the metal weighed g, what is the density of the metal? a g/ml b g/ml c g/ml d g/ml e g/ml 25. (5 points) A 3.91 gram sample of an unknown compound contains 2.01 x atoms. What is this compound s molar mass? 26. (5 points) A student weighed a piece of copper wire carefully as grams. On heating this sample with excess sulfur, a product weighing 1.64grams was formed. What was the product - Cu 2 S, CuS, CuS 2, CuS 4, or another compound? Show how you obtained your answer. 6

15 27. (5 points) The density of iron is about 7.86 g/cm 3. What would be mass in kilograms of 1 cubic meter of iron? 28. (5 points) Write formulas for the following compounds: Sulfuric acid Potassium sulfide Tin (II) nitrate Sodium hydroxide Aluminum sulfate 29. (5 points) Write the names for the following compounds: PbO 2 Co(NO 3 ) 2 KI NH 4 Br NCl 3 Solubility Rules Summarized Rule General trend 1 A compound is probably soluble if it contains one of the following cations: Group IA cation: Li +, Na +, K +, Rb +, Cs + + Ammonium ion: NH 4 2 A compound is probably soluble if it contains one of the following anions: Halide: Cl -, Br -, I - except Ag +, Hg 2+ 2, and Pb 2+ compounds Nitrate (NO - 3 ), perchlorate (ClO - 4 ), acetate (CH 3 CO2 - ), sulfate (SO 2-4 ) except Ba 2+, Hg 2+ 2, and Pb 2+ sulfates 7

5. [7 points] What is the mass of gallons (a fifth) of pure ethanol (density = g/cm 3 )? [1 gallon = Liters]

5. [7 points] What is the mass of gallons (a fifth) of pure ethanol (density = g/cm 3 )? [1 gallon = Liters] 1 of 6 10/20/2009 3:55 AM Avogadro s Number, N A = 6.022 10 23 1. [7 points] Given the following mathematical expression: (15.11115.0)/(2.154 10 3 ) How many significant figures should the answer contain?