EXPERIMENT 17 Acid-Base Equilibria and the Preparation of Buffer Solutio Analysi

Question

EXPERIMENT 17 Acid-Base Equilibria and the Preparation of Buffer Solutio Analysis: Part I Determination of Ka or Kb for an Unknown Solution Based on your knowledge of equilibrium, calculate the following. Show your work: [H,0 lin unknown solution, at equilibrium: Concentration of molecular form of acid or base at equilibrium: If acidic, give the value of K If basic, give the value of Kb: Part III: of the Buffer Solution recommended you use a Use your data to make a plot of pH vs. volume of acid added. It is it should spreadsheet program such as Excel. sure your x-axis begins t zero added acid

Explanation / Answer

Answer:

Part (I):

pH = 8.29

[H3O+] = 10-pH = 10-8.29 = 5.13 x 10-9

[H3O+] = 5.13 x 10-9 M

As pH > 7 solution is basic.

pOH = 14 - 8.29 = 5.71

[HO-] = 10-pOH

[HO-] = 10-5.71.

[HO-] = 2.0 x 10-6.  --------- (1)

A monoacidic base say HA ionizes as,

A + H-OH <-------> AH(aq) + HO- (aq)

Kb = [HO-][AH] / [A] ------------ (2)

Stoichiometric relationship says,

[HO-] = [AH] = 2.0 x 10-6 M ---------- (at equilibrium)

[A] = (0.100 - 2.0 x 10-6) M ------------- (at equilibrium)

as 0.1 >> 2.0 x 10-6. we have 0.100 - 2.0 x 10-6 = 0.1 (apprx.)

[HA] = 0.100 M

Using these values in eq.(2)

Kb = (2.0 x 10-6)(2.0 x 10-6) / (0.1)

Kb = 4.0 x 10-11.

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