CH302 Homework 7-solutions

CH302 Homework 7-solutions - Bodet(ngb299 Homework 7...

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Bodet (ngb299) – Homework 7 – sutcli ff e – (51630) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. ”Everything you never wanted to know about bu ff ers but were forced to find out”. Don’t forget: READ the Q to find out if some of the bu ff er solution is removed from the original sample before an impurity is added. Work in moles in your ICE tables, but watch to make sure if you use a regular Ka or Kb expression, you convert back to molarities. Note: The H-H equation will be very handy here! Once more HW will cover titration curves and Ksp’s. 001 10.0 points Some solid KClO 2 is added to a water solution of HClO 2 . Which of the following statements is correct? 1. pH of the solution decreases. 2. pH of the solution increases. correct 3. [H 3 O + ] will remain the same. 4. [OH - ] of the solution decreases. Explanation: 002 10.0 points Which response identifies the statements true of bu ff er solutions? l) A bu ff er solution could consist of equal concentrations of ammonia and ammo- nium bromide. 2) A bu ff er solution could consist of equal concentrations of perchloric acid (HClO 4 ) and sodium perchlorate. 3) A bu ff er solution will change only slightly in pH upon addition of small amounts of acid or base. 4) In a bu ff er solution containing benzoic acid (C 6 H 5 COOH) and sodium benzoate (NaC 6 H 5 COO) the species that reacts with added hydroxide ion is the benzoate ion. 1. 2, 3 2. 1, 4 3. Another combination 4. 2, 3, 4 5. 1, 3 correct Explanation: HA + H 2 O A - + H 3 O + B + H 2 O BH + + OH - NH + 4 is the conjugate acid of the weak base NH 3 ; C 6 H 5 COO - is the conjugate base of the weak acid C 6 H 5 COOH. HClO 4 is a strong acid. OH - ions introduced into an acid bu ff er system removes the H 3 O + . Bu ff ers are composed of comparative amounts of a weak acid/base and its conjugate and allows only a small change in pH when an acid or base is added. 003 10.0 points Which of the following mixtures can produce a bu ff er? I) NH 3 + NaOH II) NH 3 + NH 4 Cl III) H + + OH - IV) HClO 2 + NaClO 2 V) (CH 3 ) 3 NHCl + (CH 3 ) 3 N 1. I, III, and V only 2. II only 3. IV only 4. II, IV, and V only correct 5. II, III, and IV only Explanation: A bu ff er contains a weak acid or weak base, plus the salt of that weak acid or base; or, a mixture which will have this composition after any acid-base reactions occur.
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