Question

Рассчитайте константу кислотности неизвестной одноосновной кислоты, если pH ее 0.01 М раствора равен 4.75.

Answer 1

Найдем количество кислоты, продиссоциировавшей на ионы
10^(-4.75)= 0.000018 моль/л
Константа кислотности = 0.000018 /0.01= 0.0018 или 0.18%

Answer 2

Calculation of Acid Dissociation Constant (Ka)

To calculate the acid dissociation constant (Ka) of an unknown monoprotic acid, we can use the pH of a 0.01 M solution of the acid. The pH of a solution is a measure of its acidity or alkalinity. In this case, we are given that the pH of the 0.01 M solution of the acid is 4.75.

The pH of a solution is related to the concentration of hydrogen ions ([H+]) in the solution. The relationship between pH and [H+] is given by the equation:

pH = -log[H+]

To calculate the [H+] from the given pH, we can rearrange the equation:

[H+] = 10^(-pH)

Substituting the given pH value of 4.75 into the equation, we can calculate the concentration of hydrogen ions:

[H+] = 10^(-4.75)

Using a calculator, we find that [H+] is approximately 1.78 x 10^(-5) M.

The acid dissociation constant (Ka) is defined as the ratio of the concentration of the dissociated form of the acid ([A-]) to the concentration of the undissociated form of the acid ([HA]) in a solution. For a monoprotic acid, the dissociation reaction can be represented as:

HA ⇌ H+ + A-

The equilibrium expression for this reaction is:

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

Since we know the concentration of hydrogen ions ([H+]) and the initial concentration of the acid ([HA]), we can substitute these values into the equation to calculate Ka:

Ka = ([H+][A-]) / [HA] = ([H+])^2 / [HA]

Substituting the values we calculated earlier, we have:

Ka = (1.78 x 10^(-5))^2 / 0.01

Using a calculator, we find that the acid dissociation constant (Ka) of the unknown monoprotic acid is approximately 3.17 x 10^(-10).

Please note that the above calculation assumes that the acid is a monoprotic acid and that the dissociation reaction is complete. In reality, the dissociation of acids can be influenced by various factors, such as temperature and the presence of other ions.