Chemistry 1A Fall 2012 Final Exam December 10 2012 180 min closed book Name SID GSI Name Disc Day Time A The test consists of short answer questions and 40 multiple9choice questions Put your written answers in the boxes provided Answers outside the boxes may not be considered in grading ONLY THE FIRST 20 30 WORDS WILL BE GRADED Write your name on every page of the exam Question Page Points Multiple Choice 1 40 3 12 160 Acid base equilibrium 4 4 Solubility 5 8 Bond energy 6 4 Free energy 7 4 Potential energy 8 6 Molecular orbitals 10 4 Electrochemical cells 11 12 Decomposition equilibrium 12 8 Total Score 210 Page 1 of 12 Quantum 1 Thermodynamics 1 E h G H 9 T S c H H f products 9 H f reactants Beer s Law A bc S S products 9 S reactants Ideal1Gas 1 G G f products 9 G f reactants PV nRT S qrev T for aA bB cC dD Constants 1 N0 6 02214 1023 mol91 G G RTln Q G 9 RTln K Ry 2 179874 10918 J 1312 kJ mol91 G 9 nF E Ry 3 28984 1015 Hz E E 9 RT nF lnQ k 1 38066 10923 J K91 h 6 62608 10934 J s me 9 101939 10931 kg c 2 99792 108 m s91 1eV 1 602 10919 J 1 J 1 kg m2 s92 T K T C 273 15 Ptotal PA PB XAPA XBPB Acid1Base 1 pH 9 log H3O pX 9 log X F 96 485 C mol 1 V 1 J C 1 nm 1099 m 1 kJ 1000 J Color and Wavelength of Light 1 atm 760 mm Hg 760 torr 1 bar 1 L atm 100 J Wavelength nm 800 400 600 200 Gas Constant R 8 31451 J K91 mol91 R 8 20578 1092 L atm K91 mol91 IR Red Green Blue UV Page 2 of 12 PHOSPHORIC ACID STRUCTURE Two structures for phosphoric acid H3PO4 are shown here Both are structures that you can find in reference books to describe this molecule Note You will need to add lone pairs on the O atoms 1 O OH HO P O OH It satisfies the octet rule and there are no formal charges B It does not satisfy the octet rule and there are no formal charges C It satisfies the octet rule and there is a formal charge of 1 on the P atom and a formal charge of 1 on one O atom It does not satisfy the octet rule and there is a formal charge of 1 on the P atom and a formal charge of 1 on one O atom Which statement is correct for the structure on the right A It satisfies the octet rule and there are no formal charges B It does not satisfy the octet rule and there are no formal charges C It satisfies the octet rule and there is a formal charge of 1 on the P atom and a formal charge of 1 on one O atom It does not satisfy the octet rule and there is a formal charge of 1 on the P atom and a formal charge of 1 on one O atom The average phosphorus oxygen bond length in H3PO4 is less than a P O single bond Many textbooks make the claim that the structure on the right with P O is the best representation for H3PO4 Do you agree with this claim A I agree P O double bonds are shorter than P O single bonds B I do not agree P O double bonds are longer than P O single bonds C I do not agree Hydrogen bonds cause the phosphorus oxygen bonds to be shorter in both representations of the molecule I think that both are good models The formal charges on the P and O atoms for the structure on the left can also explain a shorter average bond length D 4 P A D 3 HO OH Which statement is correct for the structure on the left D 2 OH A concentrated aqueous solution of phosphoric acid is extremely viscous It pours like syrup How can you explain this observation A There are strong hydrogen bonds with water which restrict molecular motion B Phosphoric acid is a polymer The polymer chains get tangled with one another C Phosphoric acid is a strong acid and therefore completely dissociated into ions D There are strong London dispersion forces because the molecule has many electrons Page 3 of 12 Name GSI PHOSPHORIC ACID EQUILIBRIA H aq H2PO4 aq Ka1 7 3 10 3 H2PO4 aq H2O l H aq HPO42 aq Ka2 6 3 10 8 HPO42 aq H2O l H aq PO43 aq Ka3 4 0 10 13 H3PO4 aq H2O l 5 What is the pH of an aqueous solution of phosphoric acid H3PO4 A pH log Ka1 2 14 B The pH is about 1 because phosphoric acid is a strong acid C The pH depends on the concentration D The H concentration is 3 times greater than in a HCl solution of equal concentration 6 What is the pH of a solution that is 0 010 M H3PO4 and 0 010 M Na3PO4 A 2 B 2 14 C 7 2 D 12 4 7 Phosphoric acid is used to give cola its tangy flavor The pH of cola is 3 0 What is the concentration of phosphoric acid A 3 0 M B 1 0 10 3 M C 7 3 10 3 M D 1 4 10 4 M 8 The pH of 100 mL of a 0 10 M H3PO4 solution is being adjusted to pH 7 by adding NaOH s How much NaOH s must be added A 0 006 mol B 0 014 mol C 0 020 mol D 0 030 mol 9 What color is a dilute solution of bromothymol blue indicator in an aqueous solution of 0 0010 M H3PO4 Ka bromothymol blue 1 0 10 7 The acid form of the indicator is yellow and the base form is blue A yellow B blue C green 10 Which species is present in the highest concentration in a solution of Na3PO4 at pH 14 A H3PO4 B H2PO4 C HPO42 D PO43 SHORT ANSWER A can of soda is 10 4 M H3PO4 and 10 1 M CO2 When cola goes flat the CO2 concentration decreases from 10 1 M to 10 2 M and one might expect a change in pH However the pH does not change Use the data provided below to explain why H3PO4 aq H2O l H aq H2PO4 aq Ka1 7 3 10 3 CO2 aq H2O l H aq HCO3 aq Ka1 4 5 10 7 Page 4 of 12 Name GSI CALCIUM PHOSPHATE SOLUBILITY Teeth are made mainly of hydroxyapatite Ca5 PO4 3 OH Consider the solubility of hydroxyapatite Ca5 PO4 3 OH s 5Ca2 aq 3PO43 aq OH aq 11 Ksp 10 36 Which equation can you use to determine the solubility x of Ca5 PO4 3 OH A Ksp 15x …