Open Question
Determine the pH of each solution. a. 0.20 M KCHO2 b. 0.20 M CH3NH3I c. 0.20 M KI
17. Acid and Base Equilibrium
pH of Weak Bases
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A 0.050 M solution of hydroxylamine, NH2OH, having Kb = 9.1 × 10^-9 has a pH of ________.
A
7.00
B
4.89
C
11.00
D
9.11
Verified step by step guidance1
Identify that hydroxylamine, NH2OH, is a weak base and will partially ionize in water. The ionization can be represented by the equation: NH2OH + H2O ⇌ NH3OH+ + OH−.
Use the base dissociation constant (Kb) expression for the weak base: Kb = [NH3OH+][OH−] / [NH2OH].
Assume that the initial concentration of NH2OH is 0.050 M and that the change in concentration due to ionization is 'x'. Therefore, at equilibrium, [NH3OH+] = x, [OH−] = x, and [NH2OH] = 0.050 - x.
Substitute these equilibrium concentrations into the Kb expression: 9.1 × 10^-9 = (x)(x) / (0.050 - x). Since Kb is very small, assume x << 0.050, simplifying the expression to 9.1 × 10^-9 ≈ x^2 / 0.050.
Solve for x to find the concentration of OH− ions, then calculate the pOH using the formula pOH = -log[OH−]. Finally, use the relationship pH + pOH = 14 to find the pH of the solution.
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