Chemistry 1A, Spring 2007 Midterm Exam 2 March 5, 2007 (90 min, closed book) Name: KEY SID: TA Name: 1.) Write your name on every page of this exam. 2.) This exam has 40 multiple choice questions. Fill in the Scantron form AND circle your answer on the exam. 3.) There is no penalty for guessing, so answer every question. 4.) Some questions may require bubbling in more than one choice to receive credit. Page 1
E = hν λν = c λ debroglie = h / p = h / mv E kin (e-) = hν - Φ = hν - hν 0 2 Z E n = R 2 n x p ~ h p = mv Particle in a box (1-D Quantum): E n = h 2 n 2 /8mL 2 ; n = 1, 2, 3... PV = nrt 3 E kin = RT 2 3RT v rms = M E = q + w w = - P ext V 3 E = nr T 2 N 0 = 6.02214 x 10 23 mol -1 R = 2.179874 x 10-18 J R = 3.28984 x 10 15 z k = 1.38066 x 10-23 J K -1 h = 6.62608 x 10-34 J s m e = 9.101939 x 10-31 kg c = 2.99792 x 10 8 m s -1 Gas Constant: R = 8.31451 J K -1 mol -1 R = 8.20578 x 10-2 L atm K -1 mol -1 T (K) = T (C) + 273.15 F = 96,485 C / mol 1 V = 1 J / C 1 nm = 10-9 m 1 kj = 1000 J Color and Wavelength of Light Wavelength (nm) 800 600 400 200 IR Red Green Blue UV G = - T S = Σ f (products) - Σ f (reactants) S = Σ S (products) - Σ S (reactants) G = Σ G f (products) - Σ G f (reactants) S = k B lnw G = - RTln K 1 S ln K = + R T R G = - nf Єº px = - log X [ A ] p = pk a + log [ A ] Page 2
SECTION 1: QUANTUM MECANICS AND ATOMIC TEORY 1.) Which of the following lists the sizes of the 1s orbitals for each species from smallest to largest? A) <e + <Li 2+ <C 5+ <Fe 25+ B) Fe 25+ <C 5+ <Li 2+ <e + < C) Fe 25+ <e + <Li 2+ < C 5+ < D) <e + < C 5+ <Fe 25+ <Li 2+ E) Need more information. 2.) Which of the following will become more paramagnetic upon ionization to form a +1 ion? Mark all that apply. A) N B) Ni C) Te D) Ba E) g 3.) From which orbital must an electron be removed from the Sr 2+ ion in its ground state to form Sr 3+? A) 5s B) 4s C) 5p D) 4p E) 3d 4.) The figure below represents part of the emission spectrum for a one-electron ion in the gas phase. The lines shown are the result of electronic transitions to the n=3 state. The wavelength of line B is 142.5 nm. What is the identity of the ion? A) e + B) e C) Li 2+ D) Be 3+ E) Be 2+ Page 3
SECTION 2: PERIODIC TABLE For the next two questions assume that the ionization energy of Na is 496 kj/mol and the electron affinity of Cl is -349 kj/mol. 5.) What is the approximate net energy change in producing Na + and Cl from Na and Cl atoms (kj/mol)? A) 147 B) 0 C) 845 D) -147 E) -845 6.) What is the net energy change in making the NaCl molecule (kj/mol)? A) -642 B) 147 C) 323 D) 510 E) 845 For the next four questions consider the following atoms: Br, Sn, Sb, Se, In. 7.) Which has the largest atomic radius? A) Br B) Sn C) Sb D) Se E) In 8.) Which is the most paramagnetic? A) Br B) Sn C) Sb D) Se E) In 9.) Which has the largest ionization energy? A) Br B) Sn C) Sb D) Se E) In 10.) Which has the largest electronegativity? A) Br B) Sn C) Sb D) Se E) In SECTION 3: BONDING 11.) Which pair has the strongest bonding interaction? A) C and B) N and C) Na and Cl D) O and Cl E) C and Cl. 12.) Which pair would form an ionic bond? A) C and B) N and C) Na and Cl D) O and Cl E) C and Cl. 13.) Which pair would form a bond that has a dipole moment? A) C and B) N and C) Na and Cl D) O and Cl E) all of these 14.) ow many resonance structures does the nitrate ion (NO 3 ) have? A) 0 B) 1 C) 2 D) 3 E) 4 Page 4
15.) What is the NO bond order in NO 3? A) 1 B) 1 1/3 C) 1 1/2 D) 1 2/3 E) 2 16.) What is the formal charge of the central atom in sulfur trioxide SO 3? A) -2 B) -1 C) 0 D) +1 E) +2 17.) What is the electronic geometry in the molecule SO 3? A) tetrahedral B) trigonal pyramidal C) bent D) trigonal planar E) square planar 18.) What is the OSO bond angle in SO 2 Cl 2? A) ~90 o B) ~120 o C) ~180 o D) ~109.5 o E) ~45 o 19.) What is the hybridization of the central atom in SF 4? A) sp B) sp 2 C) sp 3 D) sp 3 d E) sp 3 d 2 20.) What is the molecular geometry in the molecule SF 4? A) tetrahedral B) trigonal bipyramidal C) see-saw D) t-shaped E) square pyramidal 21.) Which of the following molecules has a molecular structure most similar to C 4? A) SF 4 B) XeF 4 C) SiCl 4 D) N 3 E) None of these 22.) Which of the following molecules is polar? Mark all that apply. A) SO 2 F 2 B) SO 3 C) SF 4 D) SF 6 E) C 4 Page 5
23.) ow many sigma (s) bonds are in the biacetyl complex shown below? A) 9 B) 10 C) 11 D) 12 E) 13 24.) Molecular orbitals are similar to hybrid orbitals in that? A) They both are spherically symmetric. B) Both can be formed from combinations of atomic orbitals. C) Both are pi bonding orbitals. D) Both can be formed on a single atom. E) None are true. 25.) ow many valid structural isomers exist for the molecular formula C 6 14? A) 1 B) 2 C) 3 D) 5 E) 7 26.) In which of the following molecules is the carbon-carbon bond likely to be the strongest? A) 3 CC 3 B) 2 CC 2 C) C 3 C 2 F D) CC E) 2 CO 27.) Which process involving a photon is responsible for the conversion of O 2 triplet (two unpaired electrons) to O 2 singlet (no unpaired electrons)? A) absorption B) emission C) ionization 28.) In hydrogen cyanide the configuration is -C-N. What is the best description of the C bond? A) 2s on carbon combined with 1s on hydrogen. B) 2p on carbon combined with 2p on hydrogen. C) sp 3 on carbon combined with 1s on hydrogen. D) sp 2 on carbon combined with sp 2 on hydrogen. E) sp on carbon combined with 1s on hydrogen. Page 6
Consider the molecules and molecular ions F 2 and F 2, O 2 and O 2, and N 2 and N 2 to answer the following three questions (the relative energies of the molecular orbitals for each is shown). N 2 O 2 F 2 29.) Which of the following, according to molecular orbital theory, has the strongest bond? A) F 2 B) F 2 C) O 2 D) N 2 E) N 2 30.) Which of the following, according to molecular orbital theory, has the weakest bond? A) F 2 B) F 2 C) O 2 D) N 2 E) N 2 31.) Which of the following bonds gets weaker when the species shown is ionized? A) F 2 B) F 2 C) O 2 D) N 2 E) N 2 Use the molecular orbitals for a diatomic molecule to answer questions 32-36. A B C D E 32.) Which antibonding orbital would form between atomic s orbitals? A 33.) Which sigma bonding orbital would form between atomic p orbitals? D 34.) Which is the lowest energy sigma bonding orbital? B 35.) Which is the highest energy sigma antibonding orbital? A 36.) Which is the highest energy orbital? C Page 7
37.) Which of the following is chiral? C 3 C 3 C 3 A) C Cl B) C O C) C O D) C E) C O SECTION 4: LABORATORY 38.) A student collects data on a sunscreen with an SPF of 15. If the absorbance of a 0.17 M solution is 0.21 and the absorbance of a 0.39 M solution is 0.57, what is the molarity of a solution that has an absorbance reading of 0.88? A) 1.9 B) 1.1 C) 1.7 D) 0.54 E) 0.92 39.) If butyric acid (shown right) smells sour, which one of the following compounds is also likely to smell sour? Butyric Acid A B C D E 40.) You want to determine the concentration of an unknown base solution. You use 0.107 M Cl and titrate 20.0 ml of the unknown base solution. Upon the addition of 21.4 ml of Cl, the indicator turns green and you know that you ve reached the endpoint of the titration. What is the concentration of the base solution? A) 0.0920 M B) 0.100 M C) 0.114 M D) 0.997 M E) 1.00 M Page 8