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UI CHEM 1120 - Titrations
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Chem 1120 1st Edition Lecture 16 Outline of Last Lecture I. Common Ion EffectII. Buffer Solutionsa. Calculating pH of buffers III. Adding Acid to Water and BuffersOutline of Current Lecture I. Buffer CapacityII. Acid Base TitrationsIII. Titration CalculationsIV. Titration CurveCurrent LectureI. If sufficient acid or base is added to a buffer, it will be overwhelmed and the pH will change appreciably Buffer Capacity = the amount of acid or base a buffer can neutralize before the pH changes significantly1) More concentrated buffers have a higher buffer capacityFor example, Buffer A: 0.2 M HF and 0.1 M NaF ——> pH = 2.87Buffer B: 0.4 M HF and 0.2 M NaF ——> pH = 2.87Buffer B has twice the buffer capacity of Buffer A because it’s twice as con-centrated2) Buffer capacity is highest when the concentrations of weak acid and con-jugate base are equal 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.Example: HA = A- = 1 M; V = 1 L; find ratio before and after addition of 0.01 moles of OH-[A-]/[HA] = 1M/1M = 1.00 before [A-]/[HA] = 1.01M/0.99M = 1.02 afterExample: HA = 0.25 M and A- = 1.75 M; V = 1L; find ratio before and after addition of 0.01 moles of OH-[A-]/[HA] = 1.75M/0.25M = 7.00 before [A-]/[HA] = 1.76M/0.24M = 7.33 afterBlood is a buffered solution, its principal buffer is the bicarbonate=carbonic acid buffer, HCO3- / H2CO3Exhaling CO2 from the lungs maintains the [base]/[acid] ratio by means of the equilibria (LeChatlier)This buffer has a much higher capacity to neutralize acids than bases II. titration = the accurate measurement of the volume of solution requiredto completely react with a sampleDuring a titration, titrant is slowly added form a buret to an analyte in a flask until the equivalence point is reached. Titrant is usually a standard solution (solution of accurately known concentration). Analyte is usually a solution of unknown concentration. Equivalence point = the point at which stoichiometrically equivalent quanti-ties of reactants are brought togetherEndpoint = the point at which indicator changes color (very near to equiva-lence point)Equivalence points for acid-base titrations are determined by using indicatorsthat change color near the equivalence point or by continuous monitoring of the pH III. Review stoichiometric neutralization calculations:Example: 27.37 mL of 0.1034 M NaOHare required to neutralize 25 mL ofH2SO4. What is the molarity of theH2SO4?General strategy for titration calcula-tions: divide the curve into 4 regions1) before titrant is added (single point)2) region up to the equivalence point3) at the equivalence point (single point)4) region after the equivalence pointRegion 1: Treat as strong acid problemRegion 2: Treat as limiting reagent problemRegion 3: Treat as complete neutralizationRegion 4: Treat as limiting reagent problemIV. A titration curve is a graph where the y-axis is for the analyte pH and the x-axis is for the titrant volume added. These curves are obtained by adding small portions of titrant to an analyte, and after each addition, measuring thepH. Then you have to plot the pH vs the total volume of titrant added. Titra-tion curves yield equivalence points, the number of replaceable H+ ions, Ka and Kb values, and information required for choosing an indicator.Variables determining the features of a titration curve:acid concentration, acid strength (Ka), number of protons, base concentra-tion, base strength (Kb), number of hydroxides, analyte = acid or base, vol-ume of


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UI CHEM 1120 - Titrations

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