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Class 36 Wednesday April 21 Today s Coverage 18 Bit of Review of Acids Bases Salts Buffers 18 2 Helpful items for today Equations sheet located on Canvas Pencil pen and paper or tablet Reef open and ready to go Calculator Mastering 7 Chp 17B 19B Due Friday 4 23 at 10 pm MT See Announcement for 24 Mastering 8 Chp 18 Due Wednesday 5 5 at 10 pm MT Available this evening at 10 pm Activity 5 Acids Bases Salts Due Wednesday 4 28 at 10 pm MT Available today at 12 pm Optional Practice will be available in the Optional column in the Unit 3 grid Gen Chem Lab UTA Applications Open for Fall 21 Application is posted in the Daily Blast https docs google com forms d e 1FAIpQLSdSRB JsXlWTJmQcfIveDB6stM6r4WHuJQl6Ohz1i22W TNTA viewform Applications due by Friday 4 30 5pm MT Must have earned a B or better in the course CHGN 121 or 122 10 hr week commitment Why Get paid 12 15 hr depending on experience Showcase your science skills Grow your resume Build your leadership and communication skills The G cid 155 for the reaction N2O4 2 NO2 is 4 8 kJ Calculate K for this reaction A 4 8 B 0 021 C 1 94 D 0 14 The G cid 155 for the reaction N2O4 2 NO2 is 4 8 kJ Calculate K for this reaction G RT ln K G 4800 J 8 31 J K 298 K ln K ln K 4800 J 8 31 J K 298 K ln K 1 94 K e 1 94 K 0 14 When G 0 K 1 When G 0 the reaction is not spontaneous in that direction the reaction is reactant favored according to the K value Answer D Temperature Dependence of K Slope H rxn R y m x b K n L Plot of lnK vs 1 T in kelvins gives linear plot with slope Ho R A graph of ln K vs 1 T has a slope of 3052 What is H rxn a 25 4 kJ b 25 4 kJ c 367 J d 367 J e 3052 J Slope H rxn R Answer A H p C A H2O D C A Salt into Water H p Evaluate Cation Neutral Acidic many group 1 and 2 metals conj acid of WB NH4 CH3NH3 small highly charge Al 3 Fe 3 Evaluate Anion Neutral Basic conj base of SA conj base of WA To calculate pH A No ice table B C Ice table and Ka Ice table and Kb C NaCN A Acid B Base C Salt Is the cation A Acidic B Basic C Neutral Is the anion A Acidic B Basic C Neutral Is the salt A Acidic B Basic C Neutral Salt Neutral Basic Basic NaCN salt weak base CN base weak base 0 1 M solutions of each calculate pH A H2O HA OH 0 1 x n a 0 0 I C n a x x E 0 1 x n a x x A H2O HA OH 0 1 x n a 0 0 I C n a x x E 0 1 x n a x x Kb OH HA A pOH log OH pH 14 pOH Kb OH HA A pOH log OH pH 14 pOH Buffer Solution What It Is and How It Works A buffer solution is a solution that resists changes in its pH when small amounts of acid H or base OH are added to the solution The pH of the solution does not change less than a pH unit A buffer solution is composed of a weak base and the salt of its conjugate acid conjugate acid Example NH3 and NH4Cl NH3 and NH4 weak acid and the salt of its conjugate base conjugate base Example HF and NaF HF and F Buffer Solution What It Is and How It Works C2H3O2 1 HA aq OH A aq H3O aq aq H2O l A aq H2O l HA aq H3O A HA x x 0 10 Ka 1 8 x 10 5 pH log H3O Kb OH HA A 5 6 x 10 10 pOH log OH pH 14 pOH x x 0 10 Add WA CB pH Ka 1 8 x 10 5 CH3CO2H aq H2O l D I C E 0 10 x 0 10 x H3O 0 x x Kb 5 6 x 10 10 aq aq CH3CO2 0 10 x 0 10 x Ka H CH3CO2 CH3CO2H x 0 10 x 0 10 x x 0 10 0 10 x H 1 8 x 10 5 M pH 4 74 H3O aq Conjugate Base aq Weak Acid aq H2O l H3O CB Ka WA WA CB H3O Ka log H3O log Ka log WA CB pH pKa log CB WA pH 4 74 log 0 10 0 10 pH 4 74 Henderson Hasselbalch Equation See Equations sheet Assumes x is small Why did pH rise from 2 87 to 4 74 To calculate pH A No ice table B C Ice table and Ka Ice table and Kb Check Point Be ready to click with Reef on Fri NaCl is A Acid B Bas C Salt The cation is A Acidic B Basic C Neutral The anion is A Acidic B Basic C Neutral The salt is A Acidic B Basic C Neutral A buffer is 0 100 M in NH4Cl and 0 100 M NH3 When a small amount of hydrobromic acid HBr is added to this buffer which buffer component neutralizes the added acid a NH4 b Cl 1 c NH3 d None of the above hydrobromic acid will not be neutralized by this buffer Check Point Be ready to click with Reef on Fri Write reactions that reflect the addition of a small amount of strong acid or strong base to a buffer First we must determine if we have a buffer 1 NH4Cl and NH3 Add H3O Add OH 2 HF and NaF Add H3O Add OH Check Point Try writing out the reactions before Fri


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MINES CHEN 201 - Lecture 36 Canvas

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