Open Question
Determine the pH of each two-component solution. a. 0.050 M KOH and 0.015 M Ba(OH)2 b. 0.265 M NH4NO3 and 0.102 M HCN c. 0.075 M RbOH and 0.100 M NaHCO3 e. 0.115 M NaClO and 0.0500 M KI
17. Acid and Base Equilibrium
pH of Weak Bases
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A 20.00-mL sample of 0.150 M NH3 is being titrated with 0.200 M HCl. What is the pH after 0 mL of HCl has been added? Kb of NH3 = 1.8 × 10⁻⁵
A
7.00
B
12.75
C
11.12
D
9.25
Verified step by step guidance1
Identify the chemical species involved in the solution before any HCl is added. The solution contains NH3, which is a weak base.
Write the equilibrium expression for the dissociation of NH3 in water: NH3 + H2O ⇌ NH4+ + OH-. The equilibrium constant expression is Kb = [NH4+][OH-] / [NH3].
Use the given concentration of NH3 (0.150 M) to set up an ICE (Initial, Change, Equilibrium) table to determine the concentrations of NH4+ and OH- at equilibrium.
Assume that the initial concentration of NH4+ and OH- is 0. As NH3 dissociates, let x be the concentration of NH4+ and OH- formed at equilibrium. The concentration of NH3 at equilibrium will be 0.150 - x.
Substitute the equilibrium concentrations into the Kb expression: Kb = (x)(x) / (0.150 - x). Solve for x, which represents the [OH-], and then calculate the pOH. Finally, use the relation pH + pOH = 14 to find the pH of the solution.
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