CH 302 1st Edition Lecture 14 Outline of Last Lecture I. Clicker QuestionsII. Neutralization ReactionsIII. Common Ion EffectIV. BuffersOutline of Current Lecture I. Clicker QuestionsII. Review BuffersIII. Acid-Base TitrationsIV. Polyprotic AcidsCurrent LectureClicker Questions:1.Calculate the ratio of the molarities of acetate ions and acetic acid needed to buffer a solution at pH=5.25. The pKa of CH3COOH is 4.75.A. 1 to 3.2B. 0.32 to 1C. 3.2 to 1D. 1 to 0.32. One needs to keep an unusual microbial species alive in a laboratory setting. The microbe survives best in an alkaline environment with a pH > 9. The best choice of a buffering system would be equal molar amounts of:A) C2H5NH2, C2H5NH3+, Kb = 5.6 x 10-4 B) C6H5NH2, C6H5NH3+, Kb = 3.8 x 10-10 C) HClO2, ClO2-, Ka = 1.2 x 10-2 D) HOCl, OCl-, Ka = 3.5 x 10-83.The initial concentration of the HBr is:A) 7M B) .7M C) .007 M D) .0007 M E) 3.5MHow to calculate the pH of a Buffer:1.Is the buffer acidic or basic?2.Has addition acid or base been added to the buffer system?3.If so, complete the neutralization reaction and calculate the concentration of the buffercomponents.4.Choose the correct version of the Henderson-Hasselbalch equation5.Using the equation, calculate the pHChoosing a Buffer:The best situation is: - Relatively high concentration of conjugate acid-base partners.- One to one molar concentration will buffer against both added acid and added base.- One to one molar concentration – buffer will have a pH = pKa.Acid-Base Titration:- What is the purpose of titration?o To determine the molarity of an unknown concentration- Slowly neutralize the solution by adding a strong base/acid- Monitor the pH with each addition- pH indicators are used (color changes)- Acid Base titrations are performed to determine the concentration of an acid or base and/or the Ka of an acid or Kb of a base.- The pH can be calculated by determining the ending concentrations after a series of neutralization reactions are performed.- pKa indicates the extent of ionization of an acid Lower the pKa value, the more acidic an environment necessary to keep the acid protonatedBromophenol Blue has a pKa of around 7. When it is protonated (HA form) it is yellow, when it isdeprotonated (A- form) it is blue. What color would in be in a solution in which the pH was 9?A. BlueB.YellowC.GreenPolyprotic Acids:- Each proton has its own Ka- The first hydrogen ion comes off strongest- Harder to pull off
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