Preiaboratory assignment Exp. 7 Detennining K Name; Date Lab Section: a. For a w

Question

Preiaboratory assignment Exp. 7 Detennining K Name; Date Lab Section: a. For a weak acid (e.g., CHCOOH) that is titrated with a strong base (e.g. NaOH what species (ionsimolecules) ure presest in the solution at the stolchiometric point? b. For a weak acid (e.g, CHSCOOff) that is titrated with a strong base le g. NaOH). what species (ions/molecules) are peesent in the solution at the halfway point in the tiuation toward the stolchiometric poimt? 2. A 21.54-ml. volume of 0.130 M NaOH is required to reach the stoichiometric poim for the titration of 25.00 mL. of a 0.112 M HCI solution. Would the titration of 25.00 mL of a 0.112 M CH3COOH solution require more, less, or the same volume of the 0.130 M NaOH solution? Explain. 3. Briefly explain how the pKa for a weak acid is determined in this experiment. 4. A 23.74 mL volume of 0.0981 M NaOH was used to titrate 25.0 ml of a weak monoprotic acid solution to the stoichiometric poimt. Determine the molar concentration of the weak acid solution.

Explanation / Answer

Q1a

in stoichioemtric point

CH3COOH+ NaOH = Na+ + CH3COO- + H2O

note that

CH3COO- + H2O <-> CH3COOH + OH -

then, expect

H2O >> Na+ > CH3COO- > OH- > CH3COOH > H+

b)

if titrated up to the HALFWAY:

CH3COOH+ NaOH = Na+ + CH3COO- + H2O

50% of CH3COOH left

50% of CH3COO- formed

Na+ and H2O are also present

H+ > OH-

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