CUNY Hunter College :CHEM 102: General Chemistry I Exam Final Exam Version A and B,100% CORRECT

CUNY Hunter College :CHEM 102: General Chemistry I Exam Final Exam Version A and B Instructions: 1. Do NOT open this exam until you are told to do so. Opening the exam before the start of the exam is considered an act of Academic Dishonesty. 2. All answers must be bubbled into the scantron answer sheet. 3. No credit will be given for answers written on this exam. 4. You must use a #2 pencil to bubble in the answers on your scantron. 5. This is a multiple-­‐choice exam consisting of 30 questions (7 pages). Each question is worth 3.33 points. There is no partial credit on this exam. 6. Attached to the back of this exam you will find 3 blank pages, an appendix and a periodic table. You may remove these from the exam at your convenience. 7. On the FRONT of your scantron. • Write your last name, followed by your first name. • Write your exam version (A or B) 8. On the BACK of your scantron: • Write and bubble in BOTH your last and first name. Make sure to bubble in your names as follows: Last Name (leave a space) First Name NOTE: You must Bubble in the space on your scantron! Multiple Choice Questions: (3.33 pts each) 1) Which of the following diagrams is the best representation of a mixture that contains both an element and a compound? A B C D a. A (shows two elements – remember that an element is comprised of only 1 type of atom, but not necessarily only 1 individual atom) b. B c. C d. D (shows two elements again– remember that an element is comprised of only 1 type of atom, but not necessarily only 1 individual atom) 2) Which of the following polyatomic ions is named incorrectly? a. PO43-­‐, phosphate b. MnO4-­‐, permanganate c. NO2-­‐, nitrate d. CN-­‐, cyanide 3) Which of the following explains why carbon dioxide exists as a gas at room temperature, but water exists as a liquid? a. I only b. II only c. III only d. II and III 4) The individual molecules in a sample of SO2 are attracted to one another by a combination of . a. london dispersion forces and H-­‐bonding b. H-­‐bonding and ionic bonding c. covalent bonding and dipole-­‐dipole interactions d. london dispersion forces and dipole-­‐dipole interactions 5) Naturally occurring chlorine (Cl) consists of 2 isotopes, 35Cl and 37Cl. Their relative abundances are 75.78% and 24.22 %. How do the number of protons, neutrons and electrons for atoms of these isotopes compare? a. Each atom has the same number of protons, but a different number of neutrons and a different number of electrons. b. Each atom has the same number of electrons, but a different number of protons and a different number of neutrons. c. Each atom has the same number of protons and the same number of electrons, but a different number of neutrons. d. Each atom has the same number of protons and the same number of neutrons, but a different number of electrons. 6) Given the table of bond energies to the right, what is ΔHRXN for the formation of 1 mole of N2H4 according to the following chemical reaction: N2(g) + 2H2(g)  N2H4(g). a. 156 kJ/mol b. +156 kJ/mol c. -­‐99 kJ/mol (1.7 pts partial credit for the wrong sign) d. +99 kJ/mol (bonds broken – bonds formed) 7) Aspartame (C14H18N2O5) is a solid used as an artificial sweetener. The combustion of aspartame produces carbon dioxide gas, nitrogen gas and liquid water. What is the coefficient in front of the oxygen gas in the balanced chemical equation that represents the combustion of aspartame? a. 15 b. 16 c. 18 d. 32 8) Consider a chemical reaction in which you mix two aqueous solutions (initially each at 24 °C). After the reaction is complete you measure the temperature of the resulting mixture and find that the temperature has increased to 40 °C. This chemical reaction . a. is endothermic because energy was absorbed by the system. b. is exothermic because energy was absorbed by the system c. is endothermic because energy as released by the system. d. is exothermic because energy was released by the system. 9) What is the formula of the solid product that is formed when you mix an aqueous solution of calcium nitrate with an aqueous solution of sodium phosphate? a. NaNO3 b. NaNO2 c. Ca3(PO4)2 d. CaPO4 (you needed to recognize both the solubility and how to balance the formula – this is just as wrong as not knowing the solubility in response a so I cant give partial credit for one and not the other. You had to get it all correct here) 10) Consider the species CH3OH, CH2O and CHO2-­‐ and arrange them in order of increasing C-­‐-­‐-­‐O bond length? (from shortest C-­‐-­‐-­‐O bond to longest C-­‐-­‐-­‐O bond) a. CH3OH < CH2O < CHO2-­‐ b. CH2O < CH3OH < CHO2-­‐ c. CHO2-­‐< CH3OH < CH2O d. CH2O < CHO2-­‐< CH3OH To answer Questions 11, 12 and 13 consider the mesylate anion CH3SO3-­‐1 A student in a general chemistry class has been asked to draw all the possible resonance structures for the mesylate anion. The student has proposed the following four: A B C D 11) Which of the Lewis structures proposed by the student cannot possibly be a correct Lewis structure for the mesylate anion? a. A b. B (while this is not a resonance structure of the others it is another valid Lewis structure. This question did not ask about resonance structures, simply about possible Lewis structures and this structure is valid) c. C (this structure has too many bonds around C) d. D 12) Which one of the Lewis structures proposed by the student is not a resonance structure of the other 3? a. A b. B c. C (while this is not a possible structure at all, you had to look at the 3 valid structures and pick the one that is not a resonance structure. This structure, while incorrect, is in fact a potential resonance structure of the others) d. D 13) Which of the Lewis structures proposed by the student is the most stable resonance structure? a. A b. B c. C d. D 14) How many electrons can be described by the quantum numbers: n = 6 and l =1 a. 3 b. 6 c. 12 d. 18 15) A line spectrum of atomic mercury has a wavelength of 256 nm. When mercury emits a photon of light at this wavelength, what is the frequency of this light a. 76.7 s-­‐1 b. 1.17 x 1015 s-­‐1 c. 8.54 x 10-­‐16 s-­‐1 d. 7.76 x 10-­‐19 s-­‐1 16) Arrange the following elements in order of increasing atomic radius (from smallest to largest). a. Li < N < F < Ca b. Ca < Li < N < F (1.7 pts for the reverse sequence) c. F < N < Li < Ca d. Ca < F < N < Li 17) Which of the following species is not isoelectronic with the Ne atom? a. Cl-­‐ b. O2-­‐ c. Na+ d. Mg2+ For Questions 18 and 19, consider the Vitamin C molecule. Vitamin C is an organic molecule also known as ascorbic acid. Vitamin C has the chemical formula C6H8O6 and the skeletal structure shown to the left. Consider the complete lewis structure for vitamic C and answer the questions that follow: 18) What is the hybridization of the carbon labeled A ? a. sp b. sp2 c. sp3 d. dsp2 19) What is the electron geometry about the carbon labeled B? a. linear b. bent (the point of this question was to recognize the electron geometry thus demonstrating that you know there must be 2 more H atoms on the C according to C6H8O6. If you chose bent you do not illustrate that you know molecular vs electron) c. trigonal planar d. tetrahedral (remember there are 2 H atoms on this carbon – you know this by thinking about the formula provided and the Lewis structure) 20) How many of the following statements are correct? a. one b. two (responses II and IV are true – if you think the wrong 2 responses are correct, but you chose b you still get full credit) c. three (a pi bond is formed from the sideways overlap of 2 atomic p orbitals, not 2 hybrid orbitals – this is going to be very important in organic chemistry) d. four 21) The order of filling the molecular orbitals for BN is σ2s σ*2s π2p σ2p π2p* σ2p* Based on MO theory, which of the following statements about the BN molecule is not correct? a. The total number of electrons is 12 (this is ALL the electrons in the BN molecule, not just valence) b. The molecule has 2 pi bonds (this is true – BN has a triple bond) c. The bond order is 2 (BO = (bonding – antibonding)/2 = 6-­‐2/2 = 2 ) d. The molecule is paramagnetic. (all electrons are paired so it is in fact diamagnetic) NOTE: While I did not give you the ladder for this MO diagram I did give you the energy level sequence. I do not feel that this question was unfair. If you have paid attention to the ladders in our previous practice questions this should not have been difficult. We also spent a significant amount of time discussing that pi bonds come from the overlap of 2 p orbitals and so the pi MO must have 2 bonding and 2 antibdonding orbtials. This is a very important idea and I am afraid that I am not willing to compromise on it for partial credit. 22) How many atoms are there in 177g of magnesium chloride? a. 1.06 x 1026 atoms b. 3.39 x 1024 atoms c. 1.81 x 1024 atoms d. 1.13 x 1024 atoms (1.7 pts partial credit if you calculated for molecules not atoms) To answer questions 23 and 24 consider the following information: Vanadinite is a mineral with the chemical formula Pb5(VO4)3Cl and is one of the main industrial ores that are used for the extraction of elemental vanadium. 23) If you start with 1.21 kg of Pb5(VO4)3Cl, what is the maximum number of grams of V that can be extracted from this ore. HINT: Think about the % composition by mass of V in Vanadinite! a. 43.2 grams (1.7 pts partial credit if you forgot to consider all 3 V atoms in the formula) b. 130 grams c. 155 grams d. 173 grams 24) Once the vanadium has been extracted it can be used to produce a variety of pure vanadium oxides. One such oxide was found to contain 56.02% vanadium. What is the empirical formula of this oxide? a. V2O2 b. V2O3 c. V2O5 d. V1O3 56.02 g V / 50.94 g/mol = 1.09 n V 43.98 g O / 16 g/mol = 2.75 n O normalize to 1  divide both sides by 1.09  V1O2.52 Multiply both by 2  V2O5.04 For questions 25, 26 and 27 consider the reaction that occurs when gaseous ammonia reacts with solid copper(II)oxide: 2NH3 (g) + 3CuO (s)  N2 (g) + 3Cu (s) + 3H2O (g) 25) Which species is being reduced in this reaction? a. N2 (g) b. The N in NH3 (g) c. Cu (s) (This species has already been reduced – you must read carefully) d. The Cu in CuO (s) (goes from +2 charge to 0 charge  electrons are gained) 26) If you react 18.1 g of NH3 with 90.4 g of CuO, what is the maximum amount of N2 gas that you can form? a. 79.6 grams b. 29.7 grams c. 14.84 grams d. 10.4 grams 27) What volume of NH3 is required to completely react 45.2 g of CuO at STP? CHECK THIS a. 8.5 L b. 9.82 L c. 13.4 L d. 12.7 L (1.7 pts partial credit if you forgot to consider the 2:3 mole ratio) 28) Consider a sample of nitrogen gas held at a constant temperature of 300 K. At what pressure will this sample have a density of 2.00 g/L? a. 0.002 atm b. 0.95 atm c. 1.76 atm d. 3.42 atm 29) Which of the following statements about gases is NOT true? a. If a sample of gas that contains 2 moles of argon is heated from 50°C to 100°C at constant pressure, the volume of the gas will double. b. If the volume of a gas in a sealed container is changed from 2.0 L to 3.0 L at constant temperature, the pressure of the gas will decrease. c. If the number of moles of a gas is increased under constant temperature and pressure, the volume of the gas will increase. d. If the pressure of a sample of gas in a sealed container at 298K is doubled, the volume of the container decreases by a factor of 2. NOTE: If you didn't understand the factor of 2 in response d and so you chose d it means you also didn't understand that T must be in Kelvin in response a which is why you didn't recognize that response a was in fact incorrect. Partial credit is assigned when there is a single error that clearly leads to a wrong answer – that is not the case here. IN this case choosing this response would be the result of 2 separate errors. On that note -­‐ If this question had asked you to pick response a or a response that included both a and d – there would have been partial credit for the response that included both a and d. 30) If 1 mole of an unknown gas is placed in a sealed container with a fixed volume of 2.0 L and the temperature of the container is increased from 25 °C to 250 °C, which of the following properties will change? a. I only b. II only c. III only d. Both II and III (the density does not change because both moles and volume are fixed) Appendix: Some constants and equations you might find useful: h = 6.626 x 10-­‐34 Js c = 3.00 x 108 m/s R = 0.082 L-­‐atm/mol-­‐K For one electron atoms, E = (-­‐2.18x10-­‐18J) Z2/n2, where z = nuclear charge and n = principal quantum number The energy of a photon: E = hc/λ Einstein’s Equation: E = mc2 Ideal gas law: PV = nRT Kinetic energy equations: KE = (1/2) mVo2 KE = (3/2) nRT A list of Solubility Rules: • All ammonium and group 1A salts are soluble; • all nitrates are soluble; • most chlorides, bromides, and iodides are soluble except silver, mercury, and lead; • most sulfates are soluble except calcium, barium, lead, strontium • all chlorates (ClO3-­‐) and perchlorates (ClO4)-­‐ are soluble • all acetates are soluble • phosphates are insoluble (except ammonium and Group 1A) • carbonates are insoluble (same exceptions) • hydroxides are insoluble (except ammonium, Group 1A, barium, strontium, calcium) • sulfides are insoluble (except ammonium, Group 1A, magnesium, calcium, barium)