Chem GENERAL CHEMISTRY I

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1 General Chemistry I CHEM 205 /2 02 Final Examination December 16, Dr. Cerrie Rogers x periodic table provided x non-programmable calculators allowed Chem GENERAL CHEMISTRY I LAST NAME STUDENT NUMBER FIRST NAME SIGNATURE PLEASE READ THIS PAGE WHILE YOU WAIT TO START. Check that you have 13 pages, including this page. Write your ID # on all pages. A periodic table and useful information are provided; you CAN remove those pages. Non-programmable calculators are allowed; cell phones & electronic dictionaries are not. There are multiple choice, fill-in-blanks, calculations & short-answer questions. Write all answers in the space provided (use the backs of the pages for rough work). SHOW DETAILED, ORGANIZED CALCULATIONS, or you will NOT get full marks. Suggestion if you spend 15 min / page you'll have 30 min. extra to check your work. GOOD LUCK! PLEASE RAISE YOUR HAND IF YOU NEED CLARIFICATION. Mark breakdown Page 2. / 12 Page 3. / 14 Page 4. / 7 Page 5. / 9 Page 6. / 10 Page 7. / 10 Page 8. / 10 Page 9. / 10 Page 10. / 12 Page 11. / 10 TOTAL / 100 (maximum grade 104 / 100)

2 PAGE 2 ID # PART A TRUE / FALSE & FILL-IN-THE-BLANKS QUESTIONS # 1. (10 marks) Identify the following statements as true or false. (Circle T or F.) When steam condenses to form liquid water, energy is released as heat. If species A transfers electrons to species B, then A is acting as an oxidizing agent. Precision describes how closely a measurement matches the true or accepted value. Quantization of energy levels arises naturally when electrons in atoms are treated as waves. When a chemical bond is broken, energy is released. Beryllium (Be) is an example of an alkali metal. Light is emitted by an atom when an electron moves from a higher to a lower energy level. The Thompson model of the atom included a core of positive charge called the nucleus. An atom s atomic number tells you the number of both protons and neutrons in the atom. In its elemental form, chlorine exists as diatomic molecules. # 2. (1 mark) Identify the following processes as either a CHEMICAL CHANGE or a PHYSICAL CHANGE. a) white smoke is released from dry ice, CO 2 (s) b) bubbles form when baking soda and vinegar are mixed # 3. (1 mark) Write the missing formula or name for the following compounds a) diphosphorus pentoxide b) Fe 2 O 3

3 PAGE 3 ID # # 4. (8 marks) Consider the periodic properties of the elements. a) The ion with the largest radius is I Br Rb + + Sr b) The ion with the largest ionization energy is I Br Rb + + Sr c) The two isoelectronic ions in this list are I Br Rb + + Sr d) The ion least likely to be found in a compound is I Br Rb + + Sr # 5. (3 marks) Write a balanced chemical equation for the solution-phase reaction between sulfuric acid and ammonia to produce ammonium sulfate, and identify the type of reaction involved. (aq) + (aq) ( ) Reaction type # 6. (3 marks) Draw the shape (boundary surface) of one orbital of each type named below. Label each diagram with the value of its angular momentum quantum number, l. Orbital name 2p 3d 1s Value of l Sketch of shape

4 PAGE 4 ID # PART B MULTIPLE CHOICE QUESTIONS (circle the ONE correct choice) # 7. (1 mark) You measure water in two containers a 10-mL graduated cylinder with marks at every ml, and a 1-mL pipette marked at every 0.1 ml. If you have some water in each of the containers, and add them together, to what decimal place could you measure the total? a) 0.01 ml b) 0.1 ml c) 1 ml d) 10 ml e) none of these # 8. (1 mark) Hydrogen and chlorine gases react to form HCl. You and a friend are on opposite sides of a long hallway, you with H 2 and your friend with Cl 2. You both want to form HCl in the middle of the room. Which of the following is true? a) You should release the H 2 first. b) Your friend should release the Cl 2 first. c) You both should release the gases at the same time. d) You need to know the length of the room to answer this question. e) You need to know the temperature to answer this question. # 9. (2 marks) Which of the following statements is incorrect? a) Ionic bonding results from the transfer of electrons from one atom to another. b) Dipole moments result from the unequal distribution of electrons in a molecule. c) The electrons in a polar bond are found nearer to the more electronegative element. d) A molecule with very polar bonds can be nonpolar. e) Linear molecules cannot have a net dipole moment. # 10. (2 marks) A strong line in the spectrum of atomic mercury has a wavelength of 254 nm. When mercury emits a photon of light at this wavelength, the frequency of this light is a) s -1 b) s -1 c) s -1 d) s -1 e) none of these # 11. (1 mark) When ignited, a uranium compound burns with a green flame. The wavelength of the light given off by this flame is greater than that of a) red light. b) infrared light. c) radio waves. d) ultraviolet light. e) none of these

5 PAGE 5 ID # # 12. (2 marks) Imagine you place the electrodes of a light bulb in a solution of H 2 SO 4, such that the light bulb glows brightly. You add an unknown dilute solution to this solution, and the brightness of the bulb decreases. Which of the following substances could be in the unknown solution? a) Ba(OH) 2 b) NaNO 3 c) K 2 SO 4 d) Ca(NO 3 ) 2 e) none of these # 13. (2 marks) Which of the following statements concerning lattice energy is false? a) It is often defined as the energy released when an ionic solid forms from its ions. b) MgO has a larger lattice energy than NaF. c) The lattice energy for a solid with 2+ and 2 ions is two times that for a solid with 1+ and 1 ions. d) MgO has a larger lattice energy than LiF. e) All of these are true. # 14. (1 mark) Which of the following is a reasonable criticism of the Bohr model of the atom? a) It makes no attempt to explain why the negative electron does not eventually fall into the nucleus. b) It does not adequately predict the line spectrum of hydrogen. c) It does not adequately predict the ionization energy of the valence electron(s) for elements other than hydrogen. d) It does not adequately predict the ionization energy of the 1st energy level electrons for oneelectron species for elements other than hydrogen. e) It shows the electrons to exist outside of the nucleus. # 15. (2 marks) Which of the following statements is false? a) An orbital can accommodate at most two electrons. b) The electron density at a point is proportional to the square of the wavefunction at that point. c) The spin quantum number of an electron must be either +½ or ½. d) A 2p orbital is more penetrating than a 2s; i.e., it has a higher electron density near the nucleus and inside the charge cloud of a 1s orbital. e) In the usual order of filling, the 6s orbital is filled before the 4f orbital. # 16. (1 mark) How many electrons in an atom can have the quantum numbers n = 3, l = 2? a) 2 b) 5 c) 10 d) 18 e) 6 # 17. (1 mark) The oxidation state of iodine in IO 3 is a) 0 b) +3 c) 3 d) +5 e) 5

6 Chem 205 Section 02 Fall 2005 PAGE 6 ID # # 18. (1 mark) Which of the following atoms cannot exceed the octet rule in a molecule? a) N b) S c) P d) I e) All of the atoms (a-d) can exceed the octet rule. # 19. (2 marks) Choose the correct molecular geometry (A or B), and its name, for xenon tetrafluoride. a) geometry A, which is called square pyramidal b) geometry A, which is called square planar c) geometry B, which is called T-shaped d) geometry B, which is called see-saw e) none of the above F F Xe F F # 20. (2 marks) Which choice can describe the orbital overlap involved in the Xe F bonds in XeF 4? a) 5sp 3 2sp 3 b) 4sp 3 2sp 3 c) 5sp 3 d 2 2sp 3 d) 4sp 3 d 2 2sp 3 e) none of the above A B F Xe F F F PART C SHORT ANSWER QUESTION # 21. (5 marks) Briefly explain what causes metallic iron to be attracted to a magnetic field. You must include a suitable diagram to support your explanation.

7 PAGE 7 ID # PART D SHOW-YOUR-WORK QUESTIONS show logical, well-organized work. # 22. (10 marks) When powdered zinc is heated with sulfur, a violent reaction occurs and zinc sulfide forms Unbalanced Zn(s) + S 8 (s) ZnS(s) If this reaction is done in the presence of air, some of the reactants are also consumed via reaction with O 2. a) (6 marks) Imagine that 85.2 g of Zn was reacted with 52.4 g of S 8, and g of ZnS formed. What was the percent yield of ZnS? b) (4 marks) If the remainder of the reactants combined with O 2 to form zinc oxide and sulfur dioxide, how many grams of zinc oxide formed? Include the relevant balanced chemical equation in your answer. [If you could not do part (a), assume the percent yield of the reaction with S 8 was 75%...which is incorrect.]

8 PAGE 8 ID # # 23. (10 marks) Theophylline, C 7 H 8 N 4 O 2, is a drug used to treat asthma. a) (2 marks) The recommended adult dose of theophylline is 6 mg per kg of body mass. Calculate the total dose (in milligrams) required for a 150-lb person. [Note 1 lb = g.] b) (3 marks) How many molecules of theophylline would be present in the dose calculated in part (a)? [If you could not answer part (a), choose a dose of 6 mg which is not correct.] c) (5 marks) A common way to test the purity of a substance is to perform an analysis of a sample's elemental composition, and then compare the result to the expected composition. If your sample of theophylline contains 44.2% C, 5.4% H, 28.6% N and 21.8% O by mass, is the sample pure? Show clear calculations to support your answer. What substance that might be contaminating your sample, and why can you say this?

9 PAGE 9 ID # # 24. (10 marks) Phosphate can be removed from drinking-water supplies by treating the water with calcium hydroxide, Ca(OH) 2. The following reaction occurs Balanced 5 Ca(OH) 2 (aq) + 3 PO 4 3 (aq) Ca 5 OH(PO 4 ) 3 (s) + 9 OH (aq) a) (1 mark) What type of reaction is this? Circle all that apply (You will lose marks for incorrect choices.) acid-base, gas-forming, precipitation, oxidation-reduction. b) (4 marks) How much Ca(OH) 2 is required to remove 85% of the PO 4 3 ions from L of drinking water that originally has a phosphate concentration of M? c) (5 marks) After 85% of the phosphate ions have been removed, what are the concentrations (in molarity) of PO 4 3 ions and OH ions in the solution? What would be the ph of the solution? [Note if you could not do part (b), assume that 85% of the phosphate ions = 750 moles...which is incorrect.]

10 PAGE 10 ID # # 25. PART 1 (12 marks) Ammonium nitrate, a common fertilizer, is used as an explosive in fireworks and by terrorists. The reaction that occurs when ammonium nitrate decomposes is Unbalanced NH 4 NO 3 (s) N 2 (g) + O 2 (g) + H 2 O(g) a) (10 marks) Complete the following table about the substances involved in this reaction Formula Lewis structure (include nonzero formal charges) Resonance structures (if applicable) Bond order (average) Name of molecular geometry Describe species as charged, polar, or nonpolar NH 4 + NO 3 N 2 O 2 H 2 O b) (2 marks) Draw and label the orbital overlaps involved in forming the bonds in the N 2 molecule.

11 PAGE 11 ID # # 25. PART 2 (10 marks) Ammonium nitrate, a common fertilizer, is used as an explosive in fireworks and by terrorists. The reaction that occurs when ammonium nitrate decomposes is Unbalanced NH 4 NO 3 (s) N 2 (g) + O 2 (g) + H 2 O(g) a) (1 mark) What type of reaction is the decomposition of ammonium nitrate? Circle all that apply (You will lose marks for incorrect choices.) b) (1 mark) Balance the reaction equation. acid-base, gas-forming, precipitation, oxidation-reduction. c) (5 marks) If 15.0 kg of ammonium nitrate decomposes explosively, how many liters of gas would be formed at 307 C and 1.00 atm? d) (3 marks) What would be the partial pressure of O 2 (g) in this gas mixture? Would a person be able to breathe comfortably if the air in a room was displaced by this gas mixture at normal atmospheric pressure, 1atm? Justify your answer with calculations. [Note normal air contains ~20% O 2 by mole.]

12 PAGE 12 ID # POTENTIALLY USEFUL INFORMATION Atomic mass unit 1 amu = kg Avogadro s number N = mol -1-2 Definition of Joule 1 J = 1 kg m 2 s -2 Definition of Pascal 1 Pa = 1 kg m -1 s Gas constant R = L atm mol -1 K -1 = J mol -1 K -1 Planck s constant Pressure units h = J s 760 mm Hg = 760 torr = 1 atm = kpa = bar Rydberg constant R = m -1 Speed of light c = m s -1 Electromagnetic radiation c = λν Energy of photon E = hν de Broglie s equation λ = h. mv Hydrogen atom E = - R hc n 2 Coulomb s law E = (2.31x10-19 J nm) Q 1 Q 2 r Ideal gas law PV = nrt Kinetic energy KE = ½ mv 2 Maxwell's equation u 2 = (3RT/M) Graham's law Rate of effusion of gas 1 = M of gas 2 Rate of effusion of gas 2 M of gas HAPPY HOLIDAYS

CHEM Final Exam Name

CHEM Final Exam Name CHEM 10060 Final Exam Name Conversion factors: 1 mile = 1.61 km, 1 in. = 2.54 cm, 1 kg = 2.205 lb, 1 lb = 454 g 1 L = 1.057 qt., 1 qt. = 946 ml, 4.184 J = 1 cal, 32 oz. = 1 qt., 4 qt. = 1 gallon, 2 pt.