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 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 Score 225 1 14 Quantum Thermodynamics Ideal Gas S qrev T Constants Acid Base 1 kJ 1000 J 1 atm 760 mm Hg 760 torr 1 L atm 1 bar Color and Wavelength of Light 100 J Gas Constant 2 14 Name GSI 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 2 D 2 E 3 B 109 C 120 D 180 What is the hybridization for each of the six carbon atoms in the ring structure in phenylalanine A sp 4 C 1 5 What is the approximate H O C bond angle in serine A 90 3 B 1 B sp2 C sp3 D no hybridization Which amino acid has a hydrophobic side group R A lysine B serine C methionine D phenylalanine 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 3 14 Name GSI 5 6 7 8 Which statement is true about the structure of glycine as shown above in its ionic form A The carbon atom labeled and the atoms around it all lie in the same plane B The CO2 group and the carbon atom labeled lie in the same plane C The entire molecule is planar D The geometry around the nitrogen atom is trigonal pyramidal 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 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 D The solubility is greatest at pH 14 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 D The compound is a liquid that is miscible with ethanol 4 14 Name GSI AMINO ACIDS Absorption spectra The UV Vis spectrum for phenylalanine and leucine are shown below 9 10 What color are solutions of phenylalanine and leucine A Both are colorless B Phenylalanine is red and leucine is colorless C Phenylalanine is red and leucine is black D Phenylalanine is blue and leucine is colorless 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 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 a 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 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 13 B lower C the same Lycopene absorbs light of wavelength than phenylalanine A longer B shorter C the same 5 14 Name GSI AMINO ACIDS X ray photoelectron spectra 14 15 Why is the binding energy for the 1s electrons on the oxygen atom greater than the binding energy of the 1s electrons on the nitrogen atom A The O is a smaller atom B There is more repulsion between electrons on the O atom C The O atom has a positive charge in the molecule D The N atom has a smaller nuclear charge Why are there two peaks for the carbon 1s electrons but only one peak for the oxygen 1s electron A The C atoms are bonded to different atoms B There are partial charges on the O atoms C The 1s electrons on the O atoms are both in sp hybrid orbitals D The 1s electrons on the O atoms are in resonance SHORT ANSWER The peak at a higher binding energy of 290 eV in the X ray photoelectron spectrum of carbon is due to the 1s electrons from the C atom in the CO2 group Explain why the binding energy for this electron is larger than the binding energy for the 1s electron on the C atom labeled 6 14 Name GSI AMINO ACIDS Acid base chemistry Titration curves for the solutions of 3 amino acids are shown below along with possible identities of the amino acids The buffer regions are marked on the titration curves 16 17 How do the concentrations of the three acids compare A Amino acid 2 is the most concentrated B Amino acid 3 is the most concentrated C Amino acids 2 and 3 have the same concentration and they are more concentrated than amino acid 1 D All 3 have the same concentration The concentration of a 25 mL sample of amino acid 1 is A 0 020 M 18 D 0 080 M E 0 10 M B NH3 C CO2H D CH2 E the carbon The likely identity of Amino acid 3 is A glycine 20 C 0 060 M The pKa 2 3 characterizes …