A. In the laboratory, a general chemistry student measured the pH of a 0.393 M a

Question

A. In the laboratory, a general chemistry student measured the pH of a 0.393 M aqueous solution of triethanolamine, C6H15O3N to be10.664. Use the information she obtained to determine the Kb for this base. Kb(experiment) =

B.In the laboratory, a general chemistry student measured the pH of a 0.393 M aqueous solution of ammonia to be 11.438. Use the information she obtained to determine the Kb for this base. Kb(experiment) =

C.The pH of an aqueous solution of 0.393 M phenol (a weak acid) , C6H5OH, is

D.

The hydronium ion concentration of an aqueous solution of 0.393 M formic acid, HCOOH (Ka = 1.80E-4) is

[H3O+] = _____M

Explanation / Answer

A)

pOH = 14 - 10.664 = 3.336
[OH-]= 10^-3.336 = 0.000461

the equilibrium is

C5H15O3N + H2O <=> C5H15O3NH+ + OH-

at equilibrium [OH-]= [C5H15O3NH+]

Kb = [OH-][C5H15O3NH+]/ [C5H15O3N] = (0.000461)(0.000461) / 0.393 =5.40 x 10-7

B)

pOH = 14 - 11.438 = 2.562
[OH-]= 10^-2.562 = 0.00274

NH3(aq) + HOH(l) <==> NH4+ + OH-
Kb = [NH4+] [OH-] / [NH3]

Kb = [0.00274][0.00274]/ [0.393] = 1.91 x 10-5

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