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Titration Chemistry: The Molecular Nature of Matter, 6 th edition

Titration Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson , Brady, & Hyslop acid –base, 198–199, 811– 819 redox reactions, 239–240. Titration.

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Titration Chemistry: The Molecular Nature of Matter, 6 th edition

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  1. Titration Chemistry: The Molecular Nature of Matter, 6th edition By Jesperson, Brady, & Hyslop acid–base, 198–199, 811–819 redox reactions, 239–240

  2. Titration • Titrations are a type of quantitative analysis that enables a researcher to measure the amount, not just identify, a substance in a sample. Titrations use a chemical reaction to capture all of the desired chemical species with a known reaction that produces a known product. From the amount of known product obtained the amount of the desired chemical species in the original sample can be determined. • Types of titration reactions: • Acid/Base • Redox • Components of a typical experiment: • A solution of the reactant with an unknown concentration is isolated in a beaker along with an indicator (that will change color when the reaction is complete) • The other reactant (the titrant) will be added slowly drop-wise. • The other reacted is added until the indicator changes color, meaning the reaction is complete, or has reached the endpoint. • The amount of product can be determined and then the amount of each reactant can be extrapolated.

  3. Titration: Equipment • A burette will deliver a drop of a reactant at a time. The stopcock controls the deliver of the reactant (drop or steady stream). When reading the bottom of the meniscus, you will be reading the Volume delivered, not the volume remaining in the burette. • An Erlenmeyer flask is placed below the burrette and will contain of of the reactants and the indicator. The solution will need to be constantly stirred.

  4. Titration: Example

  5. Titration: Acid Base AH + B  A- + BH+ Acid + Base  Conjugate Base + Conjugate Acid HCl + NaOH  NaCl + H2O H+ (acid) + OH- (base)  H2O (neutral water) Initial: Erlenmeyer flask: HCl + H2Owhich we can think of as H+ (aq) + Cl- (aq) Burette: NaOH + H2O which we can think of as OH- (aq) + Na+ (aq) *The pH in the Erlenmeyer flask will be low because HCl is a strong acid and there is a high concentration of H+ in solution. Midway: Erlenmeyer flask: HCl + 0.5 NaOH  H2O+ 0.5 NaCl + 0.5 HCl *Half of the neutralization reaction has happened, the pH will higher because the concentration of H+ has decreased by half. Close to Final: Erlenmeyer flask: HCl + NaOH  NaCl + H2O The neutralization reaction has been completed and the pH = 7. Final: Erlenmeyer flask: HCl + (a bit more) NaOH  NaCl + H2O + small amount of NaOH *Once ~ pH = 8 (slightly basic) has been reached the indicator will be pink and the endpoint reached.

  6. Titration: Acid Base Phenolphthalein is a common acid/base indicator that is magenta colored between pH 8.2 - 12, and colorless from 0 – 8.2. Initial Midway Final Colorless Pink

  7. Titration: Acid Base Calculations: Know: the concentration of NaOH, the Volume of NaOH added. VNaOH(L) x MNaOH (moles/L) = moles NaOH added to the acid Mole : Mole ratio of HCl: NaOH is 1:1, therefore moles NaOH added = moles of HCl reacted Determine the Molarity of the HCl solution initially by dividing the # moles that reacted with the initial volume of the solution (L).

  8. Titration: Redox • Often rely on color changes of the reactants rather then an indicator. • KMnO4 is a common redox reactant in titration experiments: • MnO4- + 5e-  Mn2+ • Powerful oxidant • Intense purple color • Reduction product is Mn2+ which is colorless • Reaction is complete when the purple color stays in the flask.

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