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Unformatted text preview: Version 061 Exam 2 Laude (52455) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. K a = [ H + ] [ A- ] [ HA ] pK a =- log K a pH =- log [H + ] pOH =- log [OH- ] [ OH- ] = ( K b C b ) 1 / 2 [ OH- ] = K b parenleftbigg C b C a parenrightbigg 10- 14 = K w [H + ] [OH- ] = K w K a K b = K w pK a + pK b = pK w 14 = pK w ( K a C a ) 1 / 2 = [ H + ] K a parenleftbigg C a C b parenrightbigg = [ H + ] [ H + ] = ( K ax K ay ) 1 / 2 pH = 0 . 5( pK ax + pK ay ) 0 = [ H + ] 2- C a [ H + ]- K w K sp = [ C ] c [ A ] a 001 6.0 points The figure below shows the titration of a monoprotic weak acid with a strong base. b b I II Volume of base added pH The pH at point I is equal to the and the pH at point II is 7. 1. p K a of the acid; greater than correct 2. pH of the acid; greater than 3. pH of the acid; less than 4. p K a of the acid; less than 5. p K a of the acid; equal to Explanation: 002 6.0 points At the stoichiometric point in the titration of 0.130 M HCOOH(aq) with 0.130 M KOH(aq), 1. the pH is less than 7. 2. [HCOOH] = 0.0650 M. 3. the pH is greater than 7. correct 4. [HCO- 2 ] = 0.130 M. 5. the pH is 7.0. Explanation: 003 6.0 points A weakly acidic solution with a pH near 7 is formed when 1 10- 7 moles of H 2 SO 3 is added to 1 liter of water. How many equations must be solved in order to accurately calculate all of the unknown concentrations formed at equilibrium in solution? 1. 2 2. 3 3. 5 correct 4. 6 5. 4 6. 1 7. 7 Explanation: There are 5 ions that make contributions in this solution: H 2 SO 3 , HSO- 3 , SO 2- 3 , H + , and OH- . 004 6.0 points The weak acid equation [H + ] = ( K a C a ) 1 / 2 can be derived from [H + ] 3 + K a [H + ] 2- ( K w + K a C a )[H + ]- K a K w = 0 Version 061 Exam 2 Laude (52455) 2 if 1. K a is negligible and C a is significantly larger than [H + ]. 2. K values are far apart, K w is negligible and C a is significantly smaller than [H + ]. 3. K values are far apart, K w is negligi- ble and C a is significantly larger than [H + ]. correct 4. K w is negligible and C a is significantly smaller than [H + ]. 5. K w is negligible and C a is significantly larger than [H + ]. Explanation: 005 6.0 points If a solution of HOCl is titrated by a strong base such as NaOH, what is the pH at the half- neutralization point of the titration ( i.e., half- way to the equivalence point)? Note: You do not need to know the initial concentration of the acid. The ionization constant is 3 . 5 10- 8 for HOCl. 1. pH = 5.5 2. pH = 6.5 3. pH = 4.5 4. pH = 3.5 5. pH = 7.5 correct Explanation: K a = 3 . 5 10- 8 At half the equivalence point, this solution is a buffer in which [HOCl] = [OCl- ]....
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