Question

Рассчитайте pH гидролиза раствора соли Na2CO3 концентрации 0,02 М

Answer 1

PH=-lg[H+]=-lg2*10^-2=2-0.301=1.699

Answer 2

Calculation of pH for the Hydrolysis of a 0.02 M Na2CO3 Solution

To calculate the pH of the hydrolysis of a 0.02 M Na2CO3 (sodium carbonate) solution, we need to consider the dissociation of the sodium carbonate and the subsequent hydrolysis of the resulting ions.

The dissociation of Na2CO3 in water can be represented as follows: Na2CO3 ⇌ 2Na+ + CO3^2-

The hydrolysis of the carbonate ion (CO3^2-) can be represented as follows: CO3^2- + H2O ⇌ HCO3- + OH-

To calculate the pH, we need to determine the concentration of the hydroxide ion (OH-) in the solution. The concentration of OH- can be calculated using the equilibrium constant expression for the hydrolysis reaction.

The equilibrium constant expression for the hydrolysis of CO3^2- is given by: Kw/Ka2 = [OH-][HCO3-]/[CO3^2-]

Where: - Kw is the ion product of water, which is equal to 1.0 x 10^-14 at 25°C. - Ka2 is the second dissociation constant of carbonic acid, which is equal to 4.8 x 10^-11.

Since the concentration of CO3^2- is equal to the concentration of Na2CO3 (0.02 M), we can substitute the values into the equilibrium constant expression and solve for [OH-].

Let's calculate the pH step by step:

1. Calculate the concentration of OH-: - Kw/Ka2 = [OH-][HCO3-]/[CO3^2-] - [OH-] = (Kw/Ka2) * [CO3^2-] - [OH-] = (1.0 x 10^-14)/(4.8 x 10^-11) * 0.02 M

2. Calculate the pOH: - pOH = -log10([OH-])

3. Calculate the pH: - pH = 14 - pOH

Let's perform the calculations:

1. Calculate the concentration of OH-: - [OH-] = (1.0 x 10^-14)/(4.8 x 10^-11) * 0.02 M - [OH-] ≈ 4.17 x 10^-4 M

2. Calculate the pOH: - pOH = -log10([OH-]) - pOH ≈ 3.38

3. Calculate the pH: - pH = 14 - pOH - pH ≈ 10.62

Therefore, the pH of the hydrolysis of a 0.02 M Na2CO3 solution is approximately 10.62.

Please note that this calculation assumes that the hydrolysis reaction is the only significant reaction occurring in the solution and that the activity coefficients are equal to 1.