Chemistry 1A Fall 010 Exam Key Chapters 4 (part), 5, 6, and 7 (part) You might find the following useful. 0.008314 kj ΔH = ΔE + (Δn)RT R = K mol 0.00418 kj q = C calδt + m w g C H rxn = Σ H f (products) Σ H f (reactants) Thermodynamic Properties for Some Common Inorganic Substances Substance State H f kj/mol Substance State H f kj/mol Ag s 0 H g 0 AgCl s 17.04 H O g 41.83 Al s 0 H O l 85.8 Al O 3 s 1669.79 H O l 187.6 Br l 0 Hg l 0 HBr g 36.3 I s 0 C(graphite) s 0 HI g 5.94 C(diamond) s 1.90 Mg s 0 CO g 110.5 MgO s 601.8 CO g 393.5 MgCO 3 s 111.9 Ca s 0 Mg(OH) s 94.54 CaC s 59.8 N g 0 CaO s 635.55 NH 3 g 46.5 CaCO 3 s 106.88 NO g 90.37 Ca(OH) aq 100.8 NO g 33.85 Cl g 0 N O 4 g 9.66 Cu s 0 N O g 81.56 CuO s 155.3 O g 49.4 1
Substance State H f kj/mol Substance State H f kj/mol F g 0 O g 0 Fe s 0 O 3 g 14. FeO s 7 S 8(rhombic) s 0 Fe O 3 s 84. S 8(monoclinic) s 0.30 Fe 3O 4 s 1118 SO g 96.06 HCl g 9.31 SO 3 g 395.18 HF g 68.61 H S g 0.15 H g 18. ZnO s 347.98 Thermodynamic Properties for some Common Organic Substances Substance Formula State H f kj/mol Acetic acid HC H 3O l 484.1 Acetaldehyde CH 3CHO g 46.81 Acetone CH 3COCH 3 l 46.81 Acetylene C H g 6.6 Benzene C 6H 6 l 49.04 Ethanol C H 5OH l 76.98 Ethane C H 6 g 84.68 Ethylene C H 4 g 5.3 Formic acid HCO H l 409.0 Glucose C 6H 1O 6 s 174.45 Methane CH 4 g 74.85 Methanol CH 3OH l 38.66 Sucrose C 1H O 11 s 1.70
For each of the following, write the word, words, letter, letters, or number in each blank that best completes each sentence. (1½ points per blank) 1. A chemical change in which atoms of one element displace (or replace) atoms of another element in a compound is called a(n) Single-displacement reaction (displacement) reaction.. Ionize means to form ions (often as a substance dissolves in water). Dissociate means to separate into ions (often as a substance dissolves in water). 3. A(n) weak base is a substance that produces fewer hydroxide ions in water solution than particles of the substance added. 4. A(n) amphoteric substance is a substance that can act as either a Brønsted-Lowry acid and a Brønsted-Lowry base, depending on the circumstances. 5. Any chemical change in which at least one element loses electrons, either completely or partially is called oxidation. 6. Of the three units of energy calorie, dietary Calorie, and joule the joule is the smallest amount of energy. 7. Of the two forms of radiant energy ultraviolet radiation and microwaves microwaves have the longest wavelength. 8. A(n) endergonic (endogonic) change is a change that absorbs energy. A(n) endothermic change is a change that leads the system to absorb heat energy from the surroundings. 9. Thermal energy is the energy associated with the random motion of particles. 10. Heat capacity is the heat necessary to increase the temperature of an object by one kelvin (or one degree Celsius). 11. The formula and state for the standard state of manganese is Mn(s), for carbon is C(graphite), for iodine is I (s), and for sulfur is S 8(s). 1. A(n) principal energy level or shell is a collection of orbitals that have the same potential energy for a hydrogen atom. 3
13. Complete the following table. (1½ point per box) Substance Strong acid, weak acid, strong base, weak base, or neutral? Strong electrolyte, weak electrolyte, or nonelectrolyte Sodium nitrate, NaNO 3 Neutral Strong electrolyte Perchloric acid, HClO 4 Strong acid Strong electrolyte Ammonia, NH 3 Weak base Weak electrolyte Benzoic acid, C 6H 5CO H Weak acid Weak electrolyte Potassium hydrogen sulfate, NaHSO 4 Weak acid Strong electrolyte 14. A substance that is often called chromic hydroxide is used as a catalyst and as a tanning agent. It can be formed from the combination of the following two solutions. Write the complete, complete ionic, and net ionic equations for this precipitation reaction. (9 points) 3KOH(aq) + Cr(NO 3) 3(aq) 3KNO 3(aq) + Cr(OH) 3(s) 3K + (aq) + 3OH (aq) + Cr 3+ (aq) + 3NO 3)(aq) 3K + (aq) + 3NO 3 (aq) + Cr(OH) 3(s) 3OH (aq) + Cr 3+ (aq) Cr(OH) 3(s) 15. Write the oxidation number for each atom above its symbol, and identify which substance is oxidized, which substance is reduced, the oxidizing agent, and the reducing agent. (10 points) +3 +1 +7 +1 +1 1 5As4O6(s) + 8KMnO4(aq) + 18HO(l) + 5KCl(aq) Oxidized As in As 4O 6 Reduced Mn in KMnO 4 Oxidizing agent KMnO 4 Reducing agent As 4O 6 +1 +5 + 1 +1 1 0K3AsO4(aq) + 8MnCl(aq) + 36HCl(aq) 4
For the following numerical problems, be sure to show your work and put a box around your answer. 16. If 6.8 ml of a 0.150 M HCl solution neutralizes all of the Ca(OH) in 5.00 ml of a Ca(OH) solution, what is the molarity of the calcium hydroxide solution? (6 points) 3? mol Ca(OH) 6.8 ml HCl soln 0.150 mol HCl 1 mol Ca(OH) 10 ml = 3 L Ca(OH) soln 5.00 ml Ca(OH) soln 10 ml HCl soln mol HCl 1 L 17. Describe how you would make 500.0 ml of 3.00 M H SO 4 from 18.0 M H SO 4? (6 points) MDVD 3.00 M (500.0 ml) MCV C = M DV D V C= = = 83.3 ml M 18.0 M C = 0.00 M Ca(OH) Carefully add 83.3 ml 18.0 M H SO 4 to about 300 ml water in a 500-mL volumetric flask, swirl, cool, and dilute with water to 500.0 ml total. 18. How much energy is released when 1.674 kg calcium carbide, CaC, reacts with excess water in the following reaction: (8 points) CaC (s) + H O(l) C H (g) + Ca(OH) (aq) H rxn = Σ H f (products) Σ H f (reactants) H rxn = [ H f CH(g) + H f Ca(OH)(aq)] [ H f CaC(s) + H f HO(l)] = [(6.6 kj) + ( 100.8 kj)] [( 59.8 kj + ( 85.8 kj)] = 144.8 kj 3 10 g 1 mol CaC 144.8 kj? kj = 1.674 kg CaC = 378 kj 1 kg 64.100 g CaC 1 mol CaC 5
Answer the following in short answer form. (7 points each) 19. Explain why some chemical reactions absorb heat from their surroundings. Reactants products Stronger bonds weaker bonds More stable less stable Lower PE + energy released higher PE KE converted to PE Decreased KE means decreased temperature Temperature inside container < temperature outside container Heat absorbed 0. Consider the neutralization reaction between the strong acid nitric acid, HNO 3(aq) and the strong base potassium hydroxide, KOH(aq). a. Describe the mixture of the two solutions before the reaction. Your answer should include mention of the particles in solution, the attractions between these particles, and a description of what these particles are doing. At the instant that the solution of nitric acid is added to the aqueous potassium hydroxide, there are four different ions in solution surrounded by water molecules,h 3O +, NO 3, K +, and OH. The oxygen ends of the water molecules surround the hydronium and potassium cations, and the hydrogen ends of water molecules surround the nitrate and hydroxide anions. b. Describe the changes that take place during the reaction. When H 3O + ions and OH ions collide and form water molecules. c. Describe the mixture after the reaction. Your answer should include mention of the particles in solution, the attractions between these particles, and a description of what these particles are doing. The potassium and nitrate ions are unchanged in the reaction. They were separate and surrounded by water molecules at the beginning of the reaction, and they are still separate and surrounded by water molecules at the end of the reaction. 1. 6
. Describe how electrons are like vibrating guitar strings. Your answer should include mention of how the information derived from wave mathematics is similar. The wave mathematics of both the guitar string and the electron show that just as the intensity of the movement of a guitar string can vary at different positions along the string, so can the intensity of the negative charge of the electron vary at different positions outside the nucleus. The variation in the intensity of the movement of the guitar string and the electron charge can be described in terms of a standing wave. Although both the electron and the guitar string can have an infinite number of possible waveforms, only certain waveforms are possible. We can focus our attention on the waveform of varying movement for the guitar string or the varying charge intensity of the electron without having to think about the actual physical nature of the electron. 7