CHEM 1120 1nd Edition Lecture 15 Outline of Last Lecture I. Factors affecting acid strengtha. OxyacidsII. Hydrolysis of metal ionsIII. Leveling effectIV. Lewis Acids and BasesV. Common ion effectVI. Buffered solutionsa. Compositionb. How does it work?c. Calculating pHOutline of Current Lecture I. Buffers continueda. Selecting an acid/base pairb. Buffer range and capacityII. Acid – Base Titrationsa. Equivalence pointb. Endpointc. Calculationsd. What variable affect a titration curve?Current LectureI. Buffers continueda. How do you select the acid/base pair for a buffer of a specific pH?i. [acid] = [base] These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Choose an acid whose pKa is approximately equal to the desired pHiii. Solve the Henderson-Hasselbalch equation for the [base]/[acid] ratiob. Buffer range: pH range over which the buffer acts effectivelyi. pH = pKa +1 to pKa -1c. Buffer capacity: amount of acid or base a buffer can neutralize before the pH changes significantlyi. pH = pKa: optimal pH of any bufferii. More concentrated buffers have a higher buffer capacityiii. Buffer capacity is highest when the concentrations of a weak acid and conjugate base are equalII. Acid-Base Titrationsa. Titration: the accurate measurement of the volume of solution required to completely react with a sampleb. Titrant slowly added from a buret to an analyte (one you are studying) in a flask until the equivalence point is reachedc. Equivalence point: the point at which stoichiometric ally equivalent quantities of reactants are brought together (talking about moles not concentrations)d. Endpoint: the point at which indicator changes color (very near to equivalence point)e. Titration curve-y axis: analyte pH, x-axis: titrant volume addedi. Why use them? Equivalence points, number of replaceable H+ ions, Ka and Kb values, info required for choosing an indicatorf. Titration calculationsi. Before any titrant is added (single point)1. Treat as strong acid problemii. Region up to the equivalence point1. Treat as limiting reagent problemiii. A the equivalence point (a single point)1. Treat as complete neutralizationiv. Region after the equivalence point1. Treat as limiting reagent problemg. What variables determine the features of a titration curve?i. Acid concentrationii. Acid strength (Ka)iii. Number of protons iv. Base concentrationv. Base
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