Calculate the pH of a solution prepared by dissolving 0.270 mol of weak acid HA and 0.260 mol of its conjugate base in water sufficient to yield 1.00 L of solution.The of HA is
A)2.099
B)3.736
C)10.264
D)3.952
E)2.307

Question

Calculate the pH of a solution prepared by dissolving 0.270 mol of weak acid HA and 0.260 mol of its conjugate base in water sufficient to yield 1.00 L of solution.The  of HA is 
A)2.099 
B)3.736 
C)10.264 
D)3.952 
E)2.307

Quizplus · Accepted Answer

Step 1: Write the equation for the dissociation of HA:

HA ⇌ H+ + A-

Step 2: Write the expression for the acid dissociation constant (Ka) of HA:

Ka = [H+][A-]/[HA]

Step 3: Write the expression for the ion product constant (Kw) of water:

Kw = [H+][OH-] = 1.0 x 10^-14 M^2

Step 4: Write the expression for the concentration of A- in terms of the initial concentrations of HA and A-:

[A-] = (0.260 mol)/(1.00 L) = 0.260 M

Step 5: Use the equilibrium constant expression to solve for [H+]:

Ka = [H+][A-]/[HA]
[H+] = Ka[HA]/[A-]
[HA] = (0.270 mol)/(1.00 L) = 0.270 M
[H+] = (1.8 x 10^-5)(0.270 M)/(0.260 M) = 1.865 x 10^-5 M

Step 6: Calculate the pH:

pH = -log[H+] = -log(1.865 x 10^-5) = 3.736

Therefore, the pH of the solution is 3.736, and the best choice is B.

Calculate the PH of a Solution Prepared by Dissolving 0