what is the pOH of a 0.12 M solution of pyridine (Kb=1.4x10^-9) at 25 Celsius
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To find the pOH of a solution of pyridine, we can use the equation:
pOH = -log10([OH-])
First, we need to determine the concentration of hydroxide ions ([OH-]) in the solution. Since pyridine is a weak base, we can assume that it partially dissociates in water. The dissociation of pyridine can be represented as follows:
C5H5N + H2O ⇌ C5H5NH+ + OH-
From the balanced equation, we can see that for every molecule of pyridine that dissociates, one hydroxide ion is produced. Therefore, the concentration of hydroxide ions is equal to the concentration of pyridine.
Given that the concentration of pyridine is 0.12 M, the concentration of hydroxide ions ([OH-]) is also 0.12 M.
Next, we can calculate the pOH value using the equation:
pOH = -log10([OH-])
pOH = -log10(0.12)
Using a calculator, we find that the pOH of a 0.12 M solution of pyridine is approximately 0.92.
To find the pOH of a solution of pyridine, we need to use the given Kb value and the concentration of pyridine solution. The pOH is the negative logarithm (base 10) of the hydroxide ion concentration [OH-].
Step 1: Write the balanced equation for the reaction of pyridine (C5H5N) with water (H2O):
C5H5N + H2O ⇌ C5H5NH+ + OH-
Step 2: Set up the expression for the Kb equilibrium constant using the concentrations:
Kb = [C5H5NH+][OH-] / [C5H5N]
Step 3: Since we have a 0.12 M solution of pyridine, we can assume that the concentration of pyridine after dissociation ([C5H5N]) is still approximately 0.12 M, and the concentration of [C5H5NH+] is negligible compared to [C5H5N].
Step 4: Solve the Kb expression for [OH-]:
Kb = [OH-]^2 / 0.12
Step 5: Rearrange the equation to solve for [OH-]:
[OH-]^2 = Kb * 0.12
Step 6: Take the square root of both sides to find [OH-]:
[OH-] = √(Kb * 0.12)
Step 7: Calculate [OH-]:
[OH-] = √(1.4x10^-9 * 0.12)
Step 8: Calculate the pOH:
pOH = -log([OH-])
Step 9: Substitute the value for [OH-] obtained previously into the equation:
pOH = -log(√(1.4x10^-9 * 0.12))
By following these steps and performing the calculations, you can find the pOH of the pyridine solution.