1. Which of the following correctly provides evidence for the unit formula of magnesium oxide? a. The decomposition of magnesium oxide produces 1.2 g of magnesium metal and 1.6 g of oxygen gas. b. The decomposition of magnesium oxide produces 2.0 g of magnesium metal and 2.0 g of oxygen gas. c. The decomposition of magnesium oxide produces 2.4 g of magnesium metal and 1.6 g of oxygen gas. d. The decomposition of magnesium oxide produces 2.4 g of magnesium metal and 3.2 g of oxygen gas. 2. 40 g of powdered calcium metal is reacted with excess fluorine gas to produces a solid with a mass of 0.76 g. Which of the following best describes the results of this reaction? a. Fluorine gas is the limiting reactant. b. The solid likely contains some CaF. c. The solid produced is pure CaF 2. d. The solid likely contains some CaF 3. 3. The following chemical equation shows the decomposition of calcium carbonate using heat. heat CaCO 3 (s) CaO(s) + CO 2 (g) This reaction was carried out in a laboratory. The data collected is shown in the table below. How many grams of calcium oxide are produced? Item Mass (g) Dry, empty crucible 27.3 Dry crucible and calcium 32.4 carbonate Carbon dioxide gas 2.2 a. 30.2 g b. 25.1 g c. 5.1 g d. 2.9 g 1
4. The diagram at right shows the arrangement of molecules before and after a reaction. Which of the following (unbalanced) chemical equation best represents this chemical reaction? a. CO(g) + O 2 (g) CO 5 (g) b. H 2 (g) + O 2 (g) H 2 O 2 (g) c. H 2 O(g) + N 2 (g) H 2 NO 3 (g) d. CO(g) + H 2 (g) CH 3 OH(g) 5. Solid sodium metal reacts with liquid water to produce aqueous sodium hydroxide and hydrogen gas as shown by the chemical equation: 2 Na(s) + 2 H 2 O(l) 2 NaOH(aq) + H 2 (g) How many grams of water are used in this reaction to form 4.0 g or hydrogen gas? a. 8 g b. 36 g c. 72 g d. 80 g 2
6. An organic chemist synthesizes urea. The chemical equation for this reaction is shown below. In carrying out the reaction, the chemist claims that 3.4 g of ammonia (NH 3 ) combined with 5.0 g of CO 2 (g). Which of the following conclusions is consistent with this data? 2 NH 3 (g) + CO 2 (g) (NH 2 ) 2 CO(aq) + H 2 O(l) a. He made a mistake in measuring the amount of CO 2, since more than that is needed to completely react with 3.4 g of ammonia. b. He made a mistake in measuring the amount of NH 3, since more than that is needed to react with 5.0 g of carbon dioxide. c. He should adjust his reaction temperature, because his percent yield is much too low. d. CO 2 is the limiting reactant and will determine the amount of urea he is able to produce. 7. In the Haber process, nitrogen gas reacts with hydrogen gas to produce ammonia as shown in the chemical equation below. 14 g of nitrogen gas is reacted with 12 g of hydrogen. What is the mass of ammonia that will be produced from this reaction if the percent yield for this reaction is 75%? a. 6 g b. 13 g c. 17 g d. 20 g N 2 (g) + 3 H 2 (g) 2 NH 3 (g) 8. A student determines that 2.4 g of carbon reacts with 3.2 g of oxygen to form a compound with the formula of CO. Which of the following masses of oxygen would need to react with 4.8 g of carbon in order to support the Law of Definite Proportions? a. 5.5 b. 6.4 c. 9.0 d. 12.8 3
9. Why is it difficult to use the reaction of burning calcium in the air to support the Law of Conservation of Mass? a. The temperature is too high for the scales to accurately measure the mass. b. The amount of oxygen combining with the calcium is unknown. c. Burning of substances always results is a loss of mass. d. The combustion reaction releases carbon dioxide and water which is difficult to measure. 10. Potassium nitrate decomposes by the process shown in the unbalanced chemical equation below. What mass of oxygen is produced when 10.1 g of potassium nitrate is decomposed? KNO 3 (s) KNO 2 (s) + O 2 (g) a. 0.8 g b. 1.6 g c. 3.2 g d. 6.4 g 11. An analysis of element X produced the mass spectroscopy graph shown above. The average atomic mass of element X will be closest to what value? a. 306 b. 307 c. 308 d. Cannot be determined without the percent natural abundance of each isotope is determined. 4
12. The mass spectrometry printout above represents two different elements. Which is the correct combination of the two elements? a. Rh and Pd b. Pd and Ag c. Ag and Cd d. Pd and Cd 5
Isotope Mass (u or Da) Percent in nature 63 Cu 62.929601 69.17 65 Cu 64.927794 30.83 64 Zn 63.929147 48.63 66 Zn 65.926037 27.90 67 Zn 66.927131 4.10 68 Zn 67.924848 18.75 13. Shown above is a partial table of the isotopic masses and natural abundances of copper and zinc. When these data were determined using a mass spectrometer, which peaks were nearly identical? a. 63 Cu and b. 63 Cu and 65 Cu 64 Zn c. 65 Cu 66 and Zn d. 64 66 67 68 Zn, Zn, Zn, and Zn 14. Which balanced equation can represent the reaction shown in the diagram? a. C + O 2 CO 2 b. H 2 + I 2 2 HI c. H 2 + O 2 H 2 O 2 d. H 2 + O 2 2 H 2 O 6
15. Consider the reaction represented above. Given the reaction chamber shown above, which of the following represents the reaction chamber after the reaction represented above has gone to completion. Assume 100% yield. a. Diagram A b. Diagram B c. Diagram C d. Diagram D 7
16. Consider the reaction between nitrogen and hydrogen to form ammonia: N 2 + 3H 2 NH 3 Assuming that the reaction illustrated in the chamber above goes to completion, how many of each type of molecule will be present at the end of the reaction? Molecule H 2 N 2 NH 3 a. 7 1 6 b. 1 1 6 c. 1 0 5 d. 0 0 5 8
17. Given the diagram above, which balanced chemical equation best describes the reaction that occurred in the diagram? a. A + B C+ D b. A + 2B 2C + 1D c. 6A + 4B 4C + 2D d. 4A + 4B 4C + 2D 9
18. A reaction occurs between nitrogen monoxide and oxygen gas in a sealed, rigid container. The starting amounts of the reactants are shown above. Which diagram below shows the reaction after it has gone to completion? 10
19. Consider the reaction 2A + B C. The diagram above shows the starting reactants. What is the limiting reagent and how much of the other reagent is in excess. Limiting Amount of other reactant in excess Reactant a. A 1 b. B 1 c. A 2 d. B 2 20. How many grams of water are produced when excess oxygen reacts completely with 170 g of ammonia? 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) a. 90 g b. 180 g c. 270 g d. 360 g 11
21. An important reaction sequence in the industrial production of nitric acid is the following: N 2 (g) + 3H 2 (g) 2NH 3 (g) 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(l) Starting with 20.0 mol of nitrogen gas in the first reaction, how many moles of oxygen gas are required to completely react with the NH 3. a. 12.5 mol O 2 b. 20.0 mol O 2 c. 25.0 mol O 2 d. 50.0 mol O 2 Free Response 1: Sodium bicarbonate (NaHCO 3 ) decomposes upon heating above 500 K as shown in the unbalanced chemical equation below. On the other hand, sodium carbonate (Na 2 CO 3 ) does NOT decompose upon heating. Heat NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g) + H 2 O(g) A student is given 14.00 g of a mixture containing both sodium carbonate and sodium bicarbonate in a small plastic vial. After heating to the point where all the sodium bicarbonate is decomposed there is a mass loss of 2.28 g. LO 1.2, 1.3, 1.18, 3.2, 3.3, 3.4; SP 1.4, 2.2, 4.1, 4.2, 5.2, 6.2; EK 1.A.2, 1.E.2, 3.A.1, 3.A.2 a. Write a balanced equation for the decomposition of sodium bicarbonate by heating. b. Describe the process by which you would heat the mixture and determine the mass loss. c. Indicate how you would know that all the sodium bicarbonate had been decomposed. d. Determine the % of Na 2 CO 3 that was contained in the original mixture. e. Is the sodium bicarbonate or the sodium carbonate the limiting reactant? Explain your reasoning. 12
Free Response 2 Answer the following questions about mass spectroscopy. (a) The mass spectrometry printout above represents two different elements. Determine which isotopes are silver. Explain your reasoning. (b) The mass spectrum of bromine (Br 2 ) consists of three peaks, as shown above. Using the data above, determine the number of isotopes of bromine that occur in nature and determine which isotope is more abundant. 13
Free Response 3 Nitric acid is made by a sequence of reactions, shown below. 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) 2NO(g) + O 2 (g) 2NO 2 (g) 3NO 2 (g) + H 2 O(l) 2HNO 3 (l) + NO(g) If the first reaction occurs with 96.2% yield, the second reaction occurs with a 91.3% yield and the third reaction proceeds with a 91.4% yield, calculate the following: (a) The grams of nitric acid produced from 1216 grams of ammonia. (b) The percent yield for the overall process. 14