CHEM 1120 Edition 1nd Lecture 15 Outline of Last Lecture I Factors affecting acid strength a Oxyacids II Hydrolysis of metal ions III Leveling effect IV Lewis Acids and Bases V Common ion effect VI Buffered solutions a Composition b How does it work c Calculating pH Outline of Current Lecture I Buffers continued a Selecting an acid base pair b Buffer range and capacity II Acid Base Titrations a Equivalence point b Endpoint c Calculations d What variable affect a titration curve Current Lecture I Buffers continued a 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 ii Choose an acid whose pKa is approximately equal to the desired pH iii Solve the Henderson Hasselbalch equation for the base acid ratio b Buffer range pH range over which the buffer acts effectively i pH pKa 1 to pKa 1 c Buffer capacity amount of acid or base a buffer can neutralize before the pH changes significantly i pH pKa optimal pH of any buffer ii More concentrated buffers have a higher buffer capacity iii Buffer capacity is highest when the concentrations of a weak acid and conjugate base are equal Acid Base Titrations a Titration the accurate measurement of the volume of solution required to completely react with a sample b Titrant slowly added from a buret to an analyte one you are studying in a flask until the equivalence point is reached c 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 added i Why use them Equivalence points number of replaceable H ions Ka and Kb values info required for choosing an indicator f Titration calculations i Before any titrant is added single point 1 Treat as strong acid problem ii Region up to the equivalence point 1 Treat as limiting reagent problem iii A the equivalence point a single point 1 Treat as complete neutralization iv Region after the equivalence point 1 Treat as limiting reagent problem g What variables determine the features of a titration curve i Acid concentration ii Acid strength Ka iii Number of protons iv Base concentration v Base strength h
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