Chemitry 6A F2007 Dr. J.A. Mack Eam : Friday 12/7/07 (here in lecture) What will be covered on the eam? Chapter 6: 6.9-6.15 Chapter 7: All Chapter 8: All Chapter 9: 9.1-9.9 Any thing from lab a well What do I need to bring? Bring a Pencil, Eraer, Calculator and camtron form 882 11/0/07 YOU NEED TO KNOW YOUR LAB SECTION NUMBER! 11/0/07 Dr. Mack. CSUS 1 11/0/07 Dr. Mack. CSUS 2 What do I need to bring? chewing optional Scantron form 882 100 quetion jobby-doo Titration Curve: Strong Acid Strong Bae: NaOH(aq) + HCl(aq) H 2 O(l) + NaCl(aq) A titration curve plot ph v. ml of titrant added. The equivalence point i the point at which equal molar amount of acid (H O + )and bae (OH )have reacted. 7 11/0/07 Dr. Mack. CSUS 11/0/07 Dr. Mack. CSUS 4
Indicator are choen o that they change color over the deired ph range. The equivalence point for a titration will change baed upon the trength of the acid: Weaker acid (large pk a ) higher ph equivalence point. 11/0/07 Dr. Mack. CSUS 5 11/0/07 Dr. Mack. CSUS 6 HYDROLYSIS REACTIONS OF WEAK ACID SALTS Salt that contain anion of a weak acid (conjugate bae) when diolved in water will produce the acid. NaA(aq) + H 2 O(l) Thi proce i know a hydrolyi. HA(aq) + NaOH(aq) The trength of a conjugate bae depend upon the trength of the acid from which it came. The tronger an acid i, the weaker i it conjugate bae, and vie vera. A a reult, conjugate bae of very weak acid will produce higher concentration of hydroide in olution. 11/0/07 Dr. Mack. CSUS 7 HYDROLYSIS REACTIONS OF WEAK ACID SALTS The conjugate bae of a trong acid will not undergo hydrolyi: NaCl(aq) + H 2 O(l) no reaction When a alt uch a odium acetate i added to water, acetic acid form: NaC 2 H 2 O (aq) + H 2 O(l) trong bae weak acid HC 2 H 2 O (aq) + NaOH(aq) 11/0/07 Dr. Mack. CSUS 9
BUFFER SOLUTIONS: When both a weak acid and a conjugate bae are both preent in olution the olution reit change to ph. decreae add bae add acid increae Thee olution are called Buffer Solution Buffer are ueful for maintaining a certain ph range during a chemical reaction. Any added acid (H + ion) react with the conjugate bae of the weak acid. A (aq) + H + (aq) HA(aq) increae decreae Any added bae (OH ion) react with the non-ionized weak acid. OH (aq) + HA(aq) A (aq) + H 2 O(l) 11/0/07 Dr. Mack. CSUS 10 11/0/07 Dr. Mack. CSUS 11 UNBUFFERED v. BUFFERED SOLUTIONS The olution on the left i not buffered, the one on the right i. Univeral indicator wa added to each olution. When NaOH(aq) i added to each olution, the buffered olution doe not change! Notice how the ph change very little for a large number of ml added in the weak acid Buffering i occurring! When HCl(aq) i added to two freh ample, once again the buffer doe not change it ph. 11/0/07 Dr. Mack. CSUS 12 11/0/07 Dr. Mack. CSUS 1
The ph of a Buffer olution i governed by the Henderon-Haelbalch Haelbalch equation: Calculate the ph of a buffer olution that i made by adding 0.100 g of odium carbonate to 500.0 ml of a 0.100 M odium bicarbonate. pka [A ] + log [HA] weak acid HCO (aq) + H 2 O(l) CO 2 2 (aq) + H O + (aq) log[h + ] pk a = log[k a ] K a = acid diociation equilibrium contant [A ] = conjugate bae concentration (uually in the form of a alt) [HA] = weak acid concentration When preparing a buffer olution, begin by chooing a weak acid with pk a cloe to required ph. 11/0/07 Dr. Mack. CSUS 14 [A 2 ] = [CO ] conjugate bae pka [A ] + log [HA] pk a = 10.25 [HA] = [HCO ] 11/0/07 Dr. Mack. CSUS 16 Calculate the ph of a buffer olution that i made by adding 0.100 g of odium carbonate to 500.0 ml of a 0.100 M odium bicarbonate. It time to play. pka [A ] + log [A [HA] 2 ] = [CO ] pk a = 10.25 10.25 + log [HA] = [HCO ] mol 1 0.100g Na 2 CO 104.99g 0.500L = 8.54 0.100 M Anwer that quetion about chapter 9 time!!! In the Brønted theory of acid and bae, both acid and bae are defined in term of how ubtance loe or gain a. OH b. H O + c. H + d. Cl 11/0/07 Dr. Mack. CSUS 17 11/0/07 Dr. Mack. CSUS 19
A water olution i found to have a molar OH - concentration of.2 10-5. The olution would be claified a: a. acidic b. baic c. neutral d. can't be claified A olution for which [H + ] = 1.0 10 - will have a ph of a) 5.00 b).00 c) -5.00 d) -9.00 11/0/07 Dr. Mack. CSUS 20 11/0/07 Dr. Mack. CSUS 22 When an acid i analyzed by adding a meaured quantity of bae, the point at which all the acid ha reacted i correctly called: a. the equivalence point b. the neutral point c. the endpoint d. the analyi point Which of the following i a weak acid? a. HNO b. HCl c. H 2 CO d. H 2 SO 4 11/0/07 Dr. Mack. CSUS 2 11/0/07 Dr. Mack. CSUS 24
Which of the following alt would produce a baic olution (ph higher than 7) upon being diolved in pure, ditilled water? a. NaCl b. Na 2 CO Which of the following miture would repreent a buffer? a. odium chloride / hydrochloric acid b. odium ulfate / ulfuric acid c. odium acetate / acetic acid d. none of thee c. Mg(NO ) 2 d. NH 4 Cl 2 CO i the only conjugate bae of a week acid acetic acid i the only weak acid, therefore it i the only choice that can make a buffer olution. 11/0/07 Dr. Mack. CSUS 25 11/0/07 Dr. Mack. CSUS 26 The term, trong acid, refer to: a. the number of hydrogen atom attached to the acid molecule b. the peed at which it will diolve metal c. if it will caue burn to the kin d. the ability for the acid to completely diociate in olution True/Fale Sodium nitrate in water will produce a baic olution. Fale! NO i the conjugate bae of a trong acid NO (aq) + H 2 O(l) No reaction! 11/0/07 Dr. Mack. CSUS 27 11/0/07 Dr. Mack. CSUS 28
Which of the condition given i neceary for a chemical reaction to occur? a. The molecule of the reacting chemical mut be in motion. b. The molecule of the reacting chemical mut collide with one another. c. The molecule of the reacting chemical mut be of oppoite charge. d. The molecule of the reacting chemical mut be at different charge. Which of the following i mot cloely related to the term "reaction rate"? a. the temperature needed to initiate a reaction b. the poition of equilibrium when a reaction top c. the peed of a reaction d. more than one repone i correct 11/0/07 Dr. Mack. CSUS 29 11/0/07 Dr. Mack. CSUS 1 The energy required to tart ome pontaneou procee i called a. internal energy b. colliion energy c. free energy d. activation energy 11/0/07 Dr. Mack. CSUS 2 The following quetion refer to the following equilibrium in which all reactant and product are gae: CH 4 + H 2 O CH OH + H 2 + heat Indicate the effect of the changing condition on the poition of equilibrium. Referring to an equilibrium, What would happen if one were to cool the miture? Equilibrium a. hift left b. hift right c. no effect d. can hift to right or left 11/0/07 Dr. Mack. CSUS