pH of a Weak Base solution 1Consider an aqueous solution of trimethylamine.What is the pH of 0.45 mol L-1 (CH3)3N(aq)?Kb = 6.5 x 10-5Answer to 2 decimal places.

To calculate the pH of a weak base solution, we can use the formula for the ionization of a weak base in water and the definition of the base ionization constant (Kb).

Step 1: Write the ionization reaction for the weak base: (CH3)3N + H2O ⇌ (CH3)3NH+ + OH-

Step 2: Write the expression for the base ionization constant (Kb): Kb = [ (CH3)3NH+ ][ OH- ] / [ (CH3)3N ]

Step 3: Set up an ICE (Initial, Change, Equilibrium) table to find the equilibrium concentrations.

Initial: [(CH3)3N] = 0.45 M, [(CH3)3NH+] = 0, [OH-] = 0

Change: [(CH3)3N] = -x, [(CH3)3NH+] = +x, [OH-] = +x

Equilibrium: [(CH3)3N] = 0.45 - x, [(CH3)3NH+] = x, [OH-] = x

Step 4: Substitute the equilibrium concentrations into the Kb expression and solve for x: 6.5 x 10^-5 = x^2 / (0.45 - x)

Assuming x << 0.45, the equation simplifies to: x^2 = 6.5 x 10^-5 * 0.45 x = sqrt(6.5 x 10^-5 * 0.45) x = [OH-] = 0.0038 M

Step 5: Calculate the pOH: pOH = -log[OH-] = -log(0.0038) = 2.42

Step 6: Use the relationship between pH and pOH to find the pH: pH = 14 - pOH = 14 - 2.42 = 11.58

So, the pH of the 0.45 mol L-1 (CH3)3N(aq) solution is approximately 11.58.