Ch hemistry ry 1A F Fall 20110 Midterm m Exam m 2 Octob ber 13 22010 90 min m closed bbook KEY K Name SID GSI Name The T test consists of 4 short answer qu uestions and 21 multiple choice quesstions Put your writtten answers in the boxess provided Answers ouutside the boxxes may not be co onsidered in n grading Useful Eq quations and d Constants Write W your naame on every y page of thee exam pH log H pX log X Question n Page Points Score X 10 pX Kw 1 100 14 at 25 C Multiple Choice 2 8 75 Partitioniing molecular view 5 5 Partitioniing predict 6 5 Hydrangea Color 7 10 Autodissociation 8 5 Total 100 Strong aciids and basees HCl LiOH HNO3 NaOH H2SO4 KOH HClO4 HBr HI nstants Ka Acid dissoociation con CH3COOH H 1 75 100 5 NH4 5 70 100 10 6 2 10 10 HCN CH3NH3 2 3 10 11 H2CO3 4 45 100 7 CH3 3NH 1 58 100 10 Name GSI ACIDS FOUND IN FOOD Four acids found in foods are shown in the table Acid Formula Structure butyric acid C4H8O2 CH3 CH2 CH2 COOH 1 5 10 succinic acid C4H6O4 HOOC CH2 CH2 COOH 6 9 10 malic acid C4H6O5 HOOC CH2 CH OH COOH 4 0 10 tartaric acid C4H6O6 HOOC CH OH CH OH COOH 1 0 10 Ka2 Ka1 5 5 4 3 6 2 5 10 6 7 8 10 5 4 5 10 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 concentrations Page 2 of 8 Name GSI 4 5 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 Which H atom is the first to dissociate from malic acid B C E 4 A 3 D 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 7 B 4 1 C 5 6 4 D 7 0 E 12 2 2 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 Page 3 of 8 Name GSI 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 76 105 Page 4 of 8 Name GSI 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 twophase 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 Water 4 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 B C concentration would concentration would concentration would stay increase 3 decrease 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 B C Number of moles would Number of moles would Number of moles would increase decrease 3 stay the same Page 5 of 8 Name GSI 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 2propanol 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 Ka of 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 4 Page 6 of 8 Name GSI FLOWER COLOR AND SOIL The acidity of soil is thought to play an important role in determining the color of the flowers on certain plants Gardeners control the acid base properties of …