What is the [H₃O⁺] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? For HCOOH, K_a = 1.7 × 10^-4 A) 1.1 × 10^-4M B) 2.6 × 10^-4M C) 4.3 × 10^-4 M D) 6.7 × 10^-5 M E) none of the above

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Quizplus · Accepted Answer

First, we need to write the equation for the dissociation of HCOOH: HCOOH ⇌ H+ + HCOO- Next, we need to determine the direction the reaction will shift in the buffer solution. Since the buffer contains both HCOOH and HCOO-, we can use the Henderson-Hasselbalch equation: pH = pKa + log ([A-]/[HA]) where pH is the desired buffer pH, pKa is the acid dissociation constant (1.7 × 10^-4), [A-] is the concentration of the conjugate base (HCOO-), and [HA] is the concentration of the acid (HCOOH). Plugging in the values given in the problem, we get: pH = 3.77 + log (0.20/0.30) pH = 3.56 Since the buffer pH is below the pKa of HCOOH, the reaction will shift to the left to favor the undissociated acid (HCOOH) over the dissociated acid (HCOO-). Now, we can use the equation for the acid dissociation constant to calculate the concentrations of H+ and HCOO-: K_a = [H+][HCOO-]/[HCOOH] 1.7 × 10^-4 = x(0.20-x)/0.30 Solving for x, we get: x = 1.74 × 10^-5 Therefore, the concentration of H+ is also 1.74 × 10^-5 M. The total concentration of HCOO- is the sum of the initial concentration (0.20 M) and the concentration produced by dissociation (1.74 × 10^-5 M), which is approximately 0.20 M. Thus, the [H₃O⁺] in the buffer is: [H₃O⁺] = [HCOOH] + [HCOO-] [H₃O⁺] = 0.30 M + 0.20 M [H₃O⁺] = 0.50 M Finally, we can calculate the pH of the buffer using the concentration of H+ determined earlier: pH = -log[H+] pH = -log(1.74 × 10^-5) pH = 4.76 The answer is B, 2.6 × 10^-4 M.

What Is the [H3O+] in a Buffer That Consists of 0.30

What Is the [H₃O⁺] in a Buffer That Consists of 0.30