CH 201 Section FIRST NAME LAST NAME KEY Thursday November 7 2024 Test 3 Form A 1 Given the following reactions and equilibrium constants at 815 K 2 B s 3 2 O2 g B2O3 s H2 g 1 2 O2 g H2O g Kp 1 8 x 1015 Kp 4 3 x 107 Calculated K for the reaction below For full credit show the logic of how reactions were added 2B s 3 H2O g 3H2 g B2O3 s rxn 1 as is 2 B s 3 2 O2 g B2O3 s 1 8 x 1015 rxn 2 flip and x 3 3 H2O g 3H2 g 3 2 O2 g 1 4 3 x 107 3 2B s 3 H2O g 3H2 g B2O3 s 1 8 x 1015 x 1 4 3 x 107 3 2 26 x 10 8 K 2 3 x 10 8 2 sf 9 pts 2 Write out the equilibrium expression for the reaction below and determine the Zn2 in a solution in which the equilibrium buffered OH 1 2 x 10 5 Zn OH 2 s Zn2 aq 2OH aq Kc 4 5 x 10 17 Kc Zn2 OH 2 Zn2 Kc OH 2 4 5x10 17 1 2x10 5 2 3 1x10 7 K EXPRESSION Zn2 OH 2 3 pts Zn2 3 1x10 7 2 sf M 4 pts 3 Determine the value of Kc for the reaction below given that Kp 4 75 x 10 3 atm2 at 340 K Include UNITS in your answer NH4HS s NH3 g H2S g Kc 4 75 x 10 3 atm2 0 0821 atm K M x 340 K 2 ng 2 0 2 Kc Kp RT ng Kc 6 10 x 10 6 M2 Page 1 score Kc 6 10 x 10 6 3 sf M2 5 pts CH201 4 At 45 C the equilibrium concentrations for the following reaction in a 1 00 L flask were found to be NO g 0 51 M Cl2 g 0 22 M and NOCl g 0 37 M How many moles of Cl2 g must be added to make the equilibrium concentration of NOCl 0 50 M 2NO g Cl2 g 2NOCl g K228 K 2 39 initial equil 0 51 0 13 0 38 0 22 x 0 065 0 155 x 0 37 0 13 0 50 K 2 39 0 50 2 0 38 2 0 155 x 0 155 x 0 50 2 0 38 2 2 39 x 0 569 mol 5 Determine the ionization estimate and pH of a solution of 0 100 M benzoic acid C6H5COOH given that Ka is 6 5x10 5 Moles of Cl2 added 0 57 2 sf 9 pts ionization 100 x 6 5x10 5 0 100 1 2 2 549 H3O 6 5x10 5 x 0 100 1 2 2 550 x 10 3 pH log 2 550 x 10 3 2 59 ionization estimate 2 5 2 sf 3 pts pH 2 59 to the 0 01 4 pts 6 Calculate the H3O OH and the pH and for a solution with a pOH of 4 53 at 298 K This question does not require writing the solution pH 14 pOH 14 4 53 9 47 H3O 3 4 10 10 2 sf M 3 pts H3O1 10 pH 10 9 47 3 39 10 10 OH 3 0 10 5 2 sf M 3 pts OH1 10 pOH 10 4 53 2 95 10 5 pH 9 47 to 0 01 3 pts Page 2 score CH201 7 The pH of 0 034 M pyridine C5H5N in water is 9 39 at equilibrium What are its Kb and pKb Please write the net reaction of pyridine with water in a reaction table to produce a basic solution For the reaction please include charges on ions and states of matter Reaction of C5H5N with water C5H5N aq H2O l C5H5NH aq OH aq 4 pts C5H5N aq H2O l C5H5NH aq OH aq initial equil 0 03398 M 0 034 M 2 45 x 10 5 2 45 x 10 5 2 45 x 10 5 0M 0M 2 45 x 10 5 2 45 x 10 5 OH 10 14 00 9 39 2 45 x 10 5 Kb C5H5NH OH C5H5N 2 45 x 10 5 2 0 03398 1 766 x 10 8 pKb log Kb log 1 766 x 10 8 7 753 Kb 1 8 x 10 8 2 sf 6 pts pKb 7 75 to 0 01 2 pts 8a What is the pH designation of a 0 45 M NH4NO2 Circle the correction choice Show work and logic of choice for full credit 3 pts Ka of NH4 1 is 5 6 x 10 10 Kb of NO2 1 is 1 0 x 10 14 4 0 x 10 4 2 5 x 10 11 Ka Kb so solution is acidic ACIDIC 8b What is the estimated pH of a solution of 0 100 M NaHCO3 Show work and logic of choice for full credit NEUTRAL BASIC pH 6 37 10 33 2 8 35 HCO3 is amphiprotic A pH estimate is determined by taking the average of pKa1 and pKa2 for the conjugate acid H2CO3 pH 8 35 to 0 01 4 pts 9 How many grams of citric acid H3C6H5O7 molar mass 192 13 g mol must be added to 200 0 mL of 0 175 M aqueous NaH2C6H5O7 to make a pH 3 00 buffer pKa H3C6H5O7 3 15 pH pKa log mol base mol acid 3 00 3 15 log 0 200 L x 0 175 M mol acid 10 0 15 0 035 mol acid mol acid 0 04944 0 04944 mol acid x 192 13 g mol 9 499 g Page 3 9 5 g H3C6H5O7 to the 0 1 g 6 pts score CH201 10 What is the pH when 15 0 mL of 3 1 M HCl is added to 385 mL of 0 10 M KNO2 0 015 L x 3 1 mol H3O 1 L sol n 0 0465 mol H3O 1 L sol n 0 0385 mol NO2 0 385 L x 0 10 mol NO2 NO2 H3O HNO2 H2O i 0 0385 mol 0 0465 mol 0 0 0385 0 0385 0 0385 f 0 mol 0 0080 mol 0 0385 mix of H3O and HNO2 pay attention to H3O 0 0080 mol H3O 0 015 L 0 385 L 0 0200 M H3O pH log 0 0200 1 70 pH 1 70 to the 0 01 6 pts 11a What net reaction occurs with NaOH is added to NH4Cl Include charges for ions NH4 1 OH1 NH3 H2O 11b How many mL of 0 15 M sodium hydroxide NaOH must be added to 100 mL of 0 25 M acid base conj base conj acid 4 pts ammonium chloride NH4Cl to make a pH 9 00 buffer 100 mL 0 25 M 25 mmol NH4 1 1 OH1 NH3 H2O NH4 25 x 25 x i f x x 0 0 x x pH pKa log base acid 9 00 …
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