Page 1 of 15 Chemistry 1A, Fall 2011 Final Exam December 12, 2011 (180 min, closed book) Name:__________________________________ SID:___________________________________ GSI Name:________________ Test-taking Strategy In order to maximize your score on the exam: • Budget your time carefully -- don't spend too much time on one problem. • Show all work for which you want credit and don't forget to include units. • The short answer questions appear with the multiple choice questions but are not numbered. Be careful to answer every question and bubble in your answers correctly on the scantron form. Question Page Points Score Multiple Choice 3-14 176 Structure 3 7 Binding Energy 6 7 Chromatography 8 7 Protein Linkage 10 7 Protein Folding 10 7 Dipole 12 7 Buffer 13 7 Total 225 APage 2 of 15 Thermodynamics: ΔG° = ΔH° - TΔS° ΔH° = Σ ΔH°f (products) - Σ ΔH°f (reactants) ΔS° = Σ S° (products) - Σ S° (reactants) ΔG° = Σ ΔG°f (products) - Σ ΔG°f (reactants) ΔS = qrev/T for aA + bB ⇌ cC + dD ΔG =ΔG° + RTln Q ΔG° = - RTln K ΔG° = - nFΔEº ΔE = ΔEº - (RT/nF) lnQ Ptotal = PA + PB = XAPA° + XBPB° Acid Base: pH = - log[H3O+] pX = - log X badcBADCQ][][][][=RSTRHK°Δ+°Δ−=1ln][][logHAApKpHa−+=Quantum: E = hν λν = c Beer’s Law, A = εbc Ideal Gas: PV = nRT RTEkin23=M3RTvrms=Constants: N0 = 6.02214 × 1023 mol-1 Ry = 2.179874 × 10-18 J = 1312 kJ mol-1 Ry = 3.28984 × 1015 Hz k = 1.38066 × 10-23 J K-1 h = 6.62608 × 10-34 J s me = 9.101939 × 10-31 kg c = 2.99792 × 108 m s-1 1eV = 1.602×10-19 J 1 J = 1 kg m2 s-2 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 1 atm = 760 mm Hg = 760 torr ≈ 1 bar 1 L atm ≈ 100 J Gas Constant: R = 8.31451 J K-1 mol-1 R = 8.20578 × 10-2 L atm K-1 mol-1 800 600 400 200 IR Red Green Blue UV Wavelength (nm) Color and Wavelength of LightName_________________________________GSI_____________ Page 3 of 15 AMINO ACIDS: Structure and Bonding Amino acids, the building blocks of proteins, are compounds that contain both an amine group, −NH2, and a carboxylic acid group, −COOH. The generic amino acid has a side group, R, attached to the C atom between the amine and carboxylic acid groups as shown to the right. In aqueous solution at pH = 7, amino acids are ionic because the H+ from the −COOH group is transferred to the −NH2 group, as shown in the structures below. Use these structures to answer the questions below. 1. What is the bond order for the carbon-oxygen bonds in the -CO2− group? A) 0.5 B) 1 C) 1.5 [4] D) 2 E) 3 2. What is the approximate H-O-C bond angle in serine? A) 90° B) 109° [4] C) 120° D) 180° 3. What is the hybridization for each of the six carbon atoms in the ring structure in phenylalanine? A) sp B) sp2 [4] C) sp3 D) no hybridization 4. Which amino acid has a hydrophobic side group, R? A) lysine B) serine C) methionine [2] D) phenylalanine [4] SHORT ANSWER: The structures shown above describe amino acids in aqueous solutions. Draw the structure of glycine in its neutral, uncharged form. Be sure to include lone pairs of electrons. H2N-CH-COOH A lone electron pair on N, and two on each oxygen of the carboxyl groupName_________________________________GSI_____________ Page 4 of 15 5. Which statement is true about the structure of glycine as shown above in its ionic form? A) The carbon atom labeled α and the atoms around it all lie in the same plane. B) The CO2 group and the carbon atom labeled α lie in the same plane. [4] C) The entire molecule is planar. D) The geometry around the nitrogen atom is trigonal pyramidal. 6. Which statement best explains why glycine is more soluble in water than leucine? A) Glycine forms more hydrogen bonds with water than leucine. B) Glycine-glycine attractions are stronger than leucine-leucine attractions. C) The change in entropy is greater when glycine dissolves compared to leucine. D) Unlike in the case of glycine, attractions between water molecules are stronger than attractions between water and leucine. [4] 7. How does the solubility of glutamic acid depend on pH? A) The solubility does not depend on pH. B) The solubility is greatest at pH = 1. C) The solubility is greatest at pH = 7. [4] D) The solubility is greatest at pH = 14. The pKa’s of glutamic acid are: 2.2, 4.2 and 9.6 8. Monosodium glutamate is the sodium salt of glutamic acid. It is often added to food as a flavor enhancer. What properties do you expect for the pure compound at 25°C? A) The compound is a solid, with a strong smell. B) The compound is a solid, and is highly reflective. C) The compound is a solid that dissolves in water to form a basic solution. [4] D) The compound is a liquid that is miscible with ethanol.Name_________________________________GSI_____________ Page 5 of 15 AMINO ACIDS: Absorption spectra The UV-Vis spectrum for phenylalanine and leucine are shown below. 9. What color are solutions of phenylalanine and leucine? A) Both are colorless. [4] B) Phenylalanine is red and leucine is colorless. C) Phenylalanine is red and leucine is black. D) Phenylalanine is blue and leucine is colorless. 10. Which assignment best describes the absorption at 260 nm for phenylalanine? A) Stretching vibrations of the phenylalanine molecule. B) Bending vibrations of the phenylalanine molecule. C) Removal of electrons from molecular orbitals. D) Electrons move from a filled molecular orbital to an empty molecular orbital. [4] The absorbance for a 0.010 M phenylalanine solution is measured at different path lengths. Path length (cm) 0 0.5 cm 1.0 cm 1.5 cm 2.0 cm Absorbance 0 0.40 0.80 1.2 1.6 11. The absorbance of a solution of phenylalanine in cell with a 1.0 cm path length is 1.2. What is the concentration of the phenylalanine solution? A) 0.010 M B) 0.012 M C) 0.015 M [4] D) 0.018 M Lycopene (shown right) is extracted from tomatoes. A solution of lycopene is red. 12. Lycopene absorbs light of ___________ energy than phenylalanine. A) higher B) lower [4] C) the same 13. Lycopene absorbs light of ___________ wavelength than phenylalanine. A) longer [4] B) shorter C) the sameName_________________________________GSI_____________ Page 6 of 15 AMINO ACIDS: X-ray photoelectron spectra X-ray photoelectron spectra of glycine. 14. Why is the binding energy for the 1s electrons on the oxygen atom