Multiple Choice
What is the pH of a one liter solution that is 0.100 M in NH3 and 0.100 M in NH4Cl after 1.4 g of NaOH has been added? Kb for NH3 is 1.8 × 10^-5.
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17. Acid and Base Equilibrium
pH of Weak Bases
Multiple Choice
Calculate the pH of a 0.30 M solution of barium nitrite. Given that the Ka of HNO2 is 4.5 x 10^-4, what is the pH of the solution?
A
5.48
B
8.52
C
9.25
D
7.00
Verified step by step guidance1
Identify that barium nitrite, Ba(NO2)2, is a salt that will dissociate in water to form Ba^2+ and NO2^- ions. The NO2^- ion is the conjugate base of the weak acid HNO2.
Recognize that the NO2^- ion will undergo hydrolysis in water, reacting with water to form HNO2 and OH^- ions. This reaction can be represented as: NO2^- + H2O ⇌ HNO2 + OH^-.
Use the given Ka value of HNO2 to find the Kb for NO2^- using the relation Kb = Kw / Ka, where Kw is the ion-product constant of water (1.0 x 10^-14 at 25°C).
Set up an expression for the equilibrium concentrations using the Kb expression: Kb = [HNO2][OH^-] / [NO2^-]. Assume that the initial concentration of NO2^- is 0.30 M and that the change in concentration due to hydrolysis is 'x'.
Solve for 'x', which represents the concentration of OH^- ions, and then calculate the pOH of the solution. Finally, use the relation pH + pOH = 14 to find the pH of the solution.
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