Previous Question Score/Possible Points: 3/3 Total Score So Far/Total Exercise P

ID: 713568 • Letter: P

Question

Previous Question Score/Possible Points: 3/3 Total Score So Far/Total Exercise Points: 23/ 61 Scoring Scheme: 3-3-2-1 PartII., Now calculate K, the base dissociation constant for (C2H3021, acetate anion, for each of your trials from the concentrations of species at the equivalence point. Report 3 significant figures, e.g. 5.97E-10. #ofTrials initial2H3O2) 'apr02.] Vol(NaOH) pH(equiv. Pt.) [OH'] Trial 1: 30.0 Trial 2: 30.0 Trial 3: 30.0 5.50 6.35 5.35 7.18 7.55 9.23 1.51E-007 0.0394 355E-007 0.0385 1.7E0-005 0.0395 Submit Answer/Continue Quit Post-Lab Use 3 significant figures. Average pH Your Answer: 2.88 No Points Possible

Explanation / Answer

Acetate, C2H3O2- ion ionizes in water as below.

C2H3O2- (aq) + H2O (l) --------> HC2H3O2 (aq) + OH- (aq)

Due to the 1:1 nature of ionization, we must have,

[HC2H3O2] = [OH-] at equilibrium.

We define the base ionization constant, Kb as

Kb = [HC2H3O2][OH-]/[C2H3O2-] = [OH-]2/[C2H3O2-]

Plug in values and obtain

Trail

[OH-]

[C2H3O2-]

Kb = [OH-]2/[C2H3O2-]

1.51E-007

0.0394

(1.51E-007)2/(0.0394) = 5.79E-013

3.55E-007

0.0385

3.27E-012

1.70E-005

0.0395

7.32E-009