CHEM 6C Lecture 3: Ch 21 Buffers and Titrations of Acids and Bases

Redox Titrations Redox Titrations Like Monoprotic Titrations . Three (3) Regions Practice Extra Credit Titrate 100.0mL of 0.0500M Fe? with 0.100M Ce using the cell I drew at the beginning of the lecture. The equivalence point is when volume of Ce added is 50.0mL. Find the voltage of the cell at the follawing points: Bafore the equivalence point At the equivalence paint After the equivalence poi Take a reaction with Fe with a Ce4-, Cerium(IV), standard 20.0mL, 36.0mL, 50.0ml, 51.0mL and 63.0mL Use a Pt working electrode and a S.C.E reference Electroanalytical Techniques Typically two (2) types of Electroanalytical Electroanalytical Techniques Control Current-; Vary Potential - E Instrument Used: Galvanostat

Experimental Determination of pKa of buffers In this lab you. the student, will titrate several different buffer solutions in order to determine their pKa. Recall from class that (or from the water chemistry chapter of your textbook) that the pKa of a weak acid/base is equal to the pH of the solution when it population of molecules are 50% protonated/deprotonated. In this lab you will be given a butter solution (typically at low pH) and will titrate with 1 M potassium hydroxide (KOH) while measuring the pH during each stage of the process. You will then need to generate from your data a titration plot and then to extrapolate from there the pKa of the weak acid/base. General Procedure Tentative buffers to be tested: water (N = 1), 0.4 M Acetic Acid (N = 3), 0.4 M Glycine (N = 3), [N is the number if replicates] As in any lab put on your personal protective equipment (PPE): lab coal, safety glasses, and gloves Setup burette with 1 M KOH. Be careful not to spill. In a small beaker (100 mL or smaller) pour in 40 mL of buffer to be tested. Titrate until pH passes 12. Be consistent with your dispensing of KOH so your replicate trials line up appropriately. Tabulate and graph data (use formatting that is consistent with Lab 1 and include standard deviation in tables and graphs) Questions and concepts to address in the lab report Describe the buffering capacity of water based on your titration. How do they compare to Acetic Acid and Glycine? For Acetic Acid and Glycine Buffers: For titrations with N = 3. how can you account significant differences between data points? What were the pKas of your buffers based on your titration? How do they compare to those reported in the literature? How do you account for difference in values? Draw the three possible ionic forms of each buffer. Identify which of these predominates at pH 1, pH 6, and pH 11. What are the chemical equations that show how each buffers solutions at either pKa by consuming amounts of added hydrogen or hydroxide ions.

Which of the follow reactions would produce a primary alcohol? 1) NaBH4 CH,OH 21 1. LiAIH, ether 2. H,o 3) 1. excess LiAIH4, ether 2. H,o NaBH4 CH,OH он