Question

Вичеслить pH 0.017 M ростаора муравиной кислоти. -4 ( КД =2•10)

Answer 1

Ответ:

HCOOH + H2O ↔ H3O+ + HCOO-

pH = -log[H3O+]

Kd = [H3O+][HCOO-] / [HCOOH]

2•10^-4 = x^2 / (0.017 - x)

2•10^-4 = x^2 / 0.017

x = √(2•10^-4 * 0.017) = 0.00412 М

pH = -log[H3O+] = -log(0.00412) = 2.384

Answer 2

To calculate the pH of a 0.017 M solution of formic acid (HCOOH), you need to consider the dissociation of formic acid in water. Formic acid is a weak acid, so it partially dissociates into hydrogen ions (H+) and formate ions (HCOO-). The dissociation reaction can be represented as follows:

HCOOH ⇌ H+ + HCOO-

The dissociation constant (Ka) for formic acid is given as 2 × 10^-4 (or 2 × 10^-5, depending on the context).

To calculate the pH, you need to determine the concentration of H+ ions in the solution, which can be obtained by solving the equilibrium expression for the dissociation reaction.

Let x be the concentration of H+ ions in mol/L. Since the initial concentration of formic acid is 0.017 M, the concentration of H+ ions at equilibrium will be (0.017 - x) M. The concentration of HCOO- ions will also be (0.017 - x) M.

Using the Ka expression, we can write:

Ka = [H+][HCOO-] / [HCOOH]

Substituting the known values:

2 × 10^-4 = x × (0.017 - x) / 0.017

Simplifying the equation:

2 × 10^-4 = (0.017x - x^2) / 0.017

Multiplying both sides by 0.017:

0.000034 = 0.017x - x^2

Rearranging the equation:

x^2 - 0.017x + 0.000034 = 0

This is a quadratic equation, which can be solved using the quadratic formula:

x = (-b ± √(b^2 - 4ac)) / (2a)

For our equation:

a = 1, b = -0.017, c = 0.000034

Calculating the values:

x = (-(-0.017) ± √((-0.017)^2 - 4 × 1 × 0.000034)) / (2 × 1)

x = (0.017 ± √(0.000289 - 0.000136)) / 2

x = (0.017 ± √0.000153) / 2

x ≈ (0.017 ± 0.012369) / 2

Now we have two potential values for x:

x₁ ≈ (0.017 + 0.012369) / 2 ≈ 0.014685

x₂ ≈ (0.017 - 0.012369) / 2 ≈ 0.002315

Since x represents the concentration of H+ ions, we need to select the value that is physically meaningful. In this case, x₁ ≈ 0.014685 is the appropriate concentration.

Finally, to calculate the pH, we use the equation:

pH = -log[H+]

pH = -log(0.014685)

pH ≈ 1.83

Therefore, the pH of a 0.017 M solution of formic acid (HCOOH) with a dissociation constant (Ka) of 2 × 10^-4 is approximately 1.83.