Name:_ SID:___ GSI Na - T- Pco- W QuestionMultiple Partitioniview PartitioniHydrangAutodissTotal ________K_________me:______The test consut your writtonsidered inWrite your nan Choice ing-moleculing-predict ea Color ociation ChKEY______________________ists of 4 shoten answers n grading. ame on everyPage 2-8 ar 5 6 7 8 hemistryMidtermOctob(90 m____________________ rt answer quin the boxesy page of thePoints 75 5 5 10 5 100 ry 1A, Fm Examber 13, 2min, closed b_________uestions and s provided. e exam. Score Fall 201m #2 2010 book) _ 21 multiple Answers ouUseful EqpH = - logpX = - log X = 10-pX Kw = 1×10 Strong aciHCl HNO3 H2SO4 HClO4 HBr HI Acid dissoCH3COOHNH4+ HCN CH3NH3+H2CO3 (CH3)3NH+10 choice quesutside the boxquations and[H+] X 0-14 at 25°C ids and baseLiOH NaOH KOH ociation conH 1.75×105.70×106.2×10-2.3×10-4.45×10+ 1.58×10stions. xes may not d Constantses: nstants (Ka)0-5 0-10 -10 -11 0-7 0-10 be :Name_____________________GSI__________ Page 2 of 8 ACIDS FOUND IN FOOD Four acids found in foods are shown in the table. Acid Formula Structure Ka1 Ka2 butyric acid C4H8O2 CH3−CH2−CH2−COOH 1.5 × 10-5 succinic acid C4H6O4 HOOC−CH2−CH2−COOH 6.9 × 10-5 2.5 × 10-6 malic acid C4H6O5 HOOC−CH2−CH(OH)−COOH 4.0 × 10-4 7.8 × 10-6 tartaric acid C4H6O6 HOOC−CH(OH)−CH(OH)−COOH 1.0 × 10-3 4.5 × 10-5 1. What is the pH of a 0.0050 M solution of butyric acid? A) 2.3 (1) B) 3.6 (3) C) 4.1 D) 4.8 2. It takes 56 mL of 0.012 M NaOH to titrate 50 mL of succinic acid to the second equivalence point. What is the concentration of succinic acid? A) 0.0022 M B) 0.0067 M (3) C) 0.013 M (1) D) 0.026 M 3. Which of the molecules or ions listed below is present in the largest concentration when equal number of moles of butyric acid and sodium hydroxide are mixed? A) Butyric acid, CH3CH2CH2COOH B) Sodium butyrate, CH3CH2CH2COONa (3) C) OH− D) Sodium butyrate and OH− are present in roughly equal concentrationsName_____________________GSI__________ Page 3 of 8 4. Sourness is directly related to acid strength. Solid malic acid is used to coat candy to make it taste extremely sour. What could you do to make the candy taste less sour? A) Use sodium hydrogen malate, C4H5O5Na (3) B) Use solid succinic acid, C4H6O4(3) C) Use solid tartaric acid, C4H6O6 D) Both A and B (4) E) Both B and C 5. Which H atom is the first to dissociate from malic acid? 6. A solution of succinic acid is titrated with sodium hydroxide. During the titration, 15 mL of a 0.100M NaOH solution was added to 10mL of a 0.100M succinic acid solution. What is the pH of the resulting solution? A) 3.2 B) 4.1 C) 5.6 (4) D) 7.0 E) 12.2 (2) 7. Which indicator would you choose to detect the equivalence point of a titration of sodium butyrate, C4H7O2Na, with hydrochloric acid, HCl? A) methyl orange, pKa = 3.8 (4) B) methyl red, pKa = 5.0 (3) C) bromothymol blue, pKa = 7.3 D) phenol red, pKa = 8.0 E) phenolphthalein, pKa = 9.5 A (3) BCD E (4)Name_____________________GSI__________ Page 4 of 8 PARTITIONING AND THE ENVIRONMENT Environmental scientists use the octanol-water partition coefficient, KOW, to predict where a compound will remain if released into the environment. If a chemical is more soluble in the octanol, it tends to accumulate in the tissues of animals. If the chemical is more soluble in water, it tends to be easily flushed as waste by the animals. The equilibrium constant expresses the relative amounts dissolved in the two solvents. Solute (aq)  Solute (octanol) 󰇟󰇠 󰇟󰇠 Octanol, Fuel Structure logKOW KOW Methanol -0.74 0.18 Ethanol -0.30 0.50 1-Propanol 0.25 1.78 Glycerol -1.76 0.02 2-Butanol 0.65 4.47 Biodiesel (Methyl Linoleate) 6.82 6.61×106 Gasoline (isooctane) 5.83 6.76×105Name_____________________GSI__________ Page 5 of 8 8. Based on the data, which compounds are more soluble in octanol (fat) than water?A) Ethanol (2) B) Glycerol C) Methanol D) 2-Butanol (3) 9. Examine the data for ethanol. A 25 gram sample of ethanol was mixed with a two-phase mixture of 1L of water and 1L of ethanol octanol. What is the concentration (mol/L) of ethanol in the water? A) 0.18 (2) B) 0.50 C) 0.54 D) 0.36 (3) Note: all answers were accepted due to the typo in the question. The boxes below show the interface between the octanol and water. Draw in 12 molecules of ethanol, showing their distribution in the two solvents. To make the drawing easy to read use the symbol  to represent the ethanol.     Octanol 4         Water 8 10. How would the concentration of ethanol in the octanol change if the 25 grams of ethanol was added to 1L of water and only 500 mL of octanol? A concentration would increase (3) B concentration would decrease C concentration would stay the same (1) Note: A is correct. We did accept both A and C for 3 points. 11. How would the number of moles of ethanol in the octanol change if the 25 grams of ethanol was added to 1L of water and only 500 mL of octanol? A Number of moles would increase B Number of moles would decrease (3) C Number of moles would stay the sameName_____________________GSI__________ Page 6 of 8 12. Estimate the equilibrium constant, KOW, for 2-propanol (shown below). A 0.75 (4) B 1.25 (4) C 1.78 D 2.0 (3) Explain your reasoning. The 2-propanol should have a similar KOW to 1-propanol, but not identical because the structures are different. The 1-propanol is linear but 2-propanol is branched. The overall dipole moment of the 2-propanol will be slightly higher than then 1-proponal. The 1-popanol and 1-octanol molecules both have similar shapes (sausage-like) and will have greater London Forces with each other than the 2-propanol. All of these reasons mean that 2-propanol would be more attracted to the water phase which would give a slightly smaller KOW. 13. Formic acid (HCOOH) is a weak acid with a Kaof 1.8×10-4 and a KOW of 0.88. HCOOH (aq)  HCOOH (octanol) Which of the following scenarios would cause the concentration of formic acid in octanol to decrease? A) Buffer the water at a pH of 2 B) Buffer the water at a pH of 3 (3) C) Buffer the water at a pH of 5 (4) D) Adding more octanol