Calculate the pH of a 0.2M solution of Triethylamine, (C2H5)3N, with a Kb of 4.0x10^-4
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To calculate the pH of a solution of Triethylamine, you will need to use the Kb value and the concentration of the solution. Follow the steps below:
Step 1: Write the balanced chemical equation for the reaction of Triethylamine with water. In this case, Triethylamine acts as a base and reacts with water to form the conjugate acid NH4+ and OH- ions:
(C2H5)3N + H2O ⇌ NH4+ + OH-
Step 2: Write the expression for the base dissociation constant, Kb, using the concentration of the components involved:
Kb = ([NH4+][OH-])/([Triethylamine])
Step 3: Since we want to find the pH, we need to calculate the concentration of OH- ions in the solution. Based on the balanced equation, the concentration of OH- ions equals the concentration of NH4+ ions.
Step 4: Let x represent the concentration of NH4+ ions. Then, the concentration of OH- ions will also be x.
Step 5: The initial concentration of Triethylamine is 0.2 M, and we assume that the concentration of NH4+ ions is negligible compared to that. Hence, the concentration of Triethylamine will approximately remain 0.2 M after the reaction.
Step 6: Use the Kb expression to set up the equation:
4.0x10^-4 = (x)(x) / (0.2 - x)
Step 7: Solve the equation for x. Rearrange the equation to form a quadratic equation:
4.0x10^-4 = x^2 / (0.2 - x)
0.8x - x^2 = 4.0x10^-4
Step 8: Rearrange the quadratic equation and solve for x using a quadratic solver or the quadratic formula.
Step 9: Once you find the value of x, which represents the concentration of OH- ions, you can calculate the pOH by taking the negative logarithm (base 10) of the OH- concentration: pOH = -log10([OH-])
Step 10: Finally, you can calculate the pH using the relation: pH = 14 - pOH.
By following these steps, you will be able to calculate the pH of the 0.2 M solution of Triethylamine with a Kb of 4.0x10^-4.