g Calculate the pOH of a solution that results from mixing 23.3 mL of 0.16 M trimethylamine ((CH3)3N) with 44.1 mL of 0.15 M (CH3NH3Cl. The Kb value for (CH3)3N is 6.5 x 10-5.

Respuesta :

Answer:

pOH = 5.961

Explanation:

To find the pH of a weak base we can use Henderson-Hasselbalch equation for weak bases:

pOH = pKb + log [(CH₃)₃NHCl] / [(CH₃)₃N]

Where pKb is -log Kb = 4.187 and [] could be taken as moles of each specie.

Moles (CH₃)₃NHCl:

0.0441L * (0.15mol/L) = 6.615x10⁻³moles

Moles (CH₃)₃N:

0.0233L * (0.16mol/L) = 3.728x10⁻³moles

And pOH is:

pOH = pKb + log [(CH₃)₃NHCl] / [(CH₃)₃N]

pOH = 4.187 + log [6.615x10⁻³moles] / [3.728x10⁻³moles]

pOH = 5.961

The pOH of the solution is 4.44

Data;

  • Kb = 6.5* 10^-5
  • conc. (CH3)3N = 0.16M
  • volume of (CH3)3N = 23.3mL
  • conc. CH3NH3Cl. = 0.15M
  • volume of CH3NH3Cl. = 44.1mL

pOH of a solution

The pOH of a solution is calculated by

[tex]pOH = -logk_b + log \frac{[(CH3)3N]}{[CH3NH3Cl]}[/tex]

Let's find the actual concentration of the solutions

m mole of (CH3)3N = 23.3 * 0.16 = 3.728 mmol

m mol of CH3NH3Cl = 44.1 * 0.15 = 6.615 mmol

The pOH of the solution becomes

[tex]pOH = -logk_b + log \frac{[(CH3)3N]}{[CH3NH3Cl]}\\pOH = -log(6.5*10^-^5) + log (\frac{6.615}{3.728} \\pOH = -log (6.5*10^-^5) + 0.249\\pOH = 4.44[/tex]

The pOH of the solution is 4.44

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