Question

0.01 moles of a weak acid HA (\[{k_a}\] = \[2.0 \times {10^{ - 6}}\]) is dissolved in 1.0 L of 0.1 M HCl solution. The degree of dissociation of HA is? (Round off to the nearest Integer and find the answer in terms of \[{10^{ - 5}}\]). Assume the degree of dissociation << 1.

Answer 1

Hint: When an acid is dissolved in water, the covalent bond between the electronegative atom and the hydrogen atom is broken by a heterolytic fission. As a result, it releases a proton \[{H^ + }\] and a negative ion \[O{H^ - }\] . The word “degree” here stands for the “extent”.

Complete Step by Step Solution:
Dissociation in chemistry can be defined as a process in which molecules or ionic compounds, such as complexes or salts, split or separate into smaller particles such as atoms, ions or radicals, usually in a reversible manner.
Here, HA dissociates into \[{H^ + }\] and \[{A^ - }\]
                              HA ⇌ \[{H^ + }\] + \[{A^ - }\]
\[{C_1}\] 0.01 0 0
\[{C_{aq}}\] \[0.01(1 - \alpha )\] 01 \[\alpha \] + 0.1 0.01 \[\alpha \]
\[{K_\alpha }(\dfrac{{[{H^ + }][{A^ - }]}}{{[HA]}})\]
\[ \Rightarrow 2 \times {10^{ - 6}} = \dfrac{{\{ [0.1][0.01\alpha ]}}{{[0.01]}}\]
\[\alpha = 2 \times {10^{ - 5}}\]

Note: There is a basic difference between the degree of dissociation and the dissociation constant. Dissociation simply refers to the breaking down of ionic compounds into their constituents, and degree of dissociation is defined as the proportion of solute matter dissociated per mole of solution. Simply said, degree of dissociation is the number of moles of dissociated solute divided by the number of moles of solution.
A dissociation constant is a form of equilibrium constant that quantifies a bigger object's tendency to separate (dissociate) reversibly into smaller components, such as when a complex breaks down into its constituent molecules or when a salt splits up into its constituent ions. The inverse of the association constant is the dissociation constant, which is generally represented as K_d.
The dissociation constant is also known as an ionisation constant in the case of salts. The degree of dissociation is the dissociation of molecules into smaller particles, ions or radicals, whereas dissociation constant stands for the ratio of the dissociated ions to the undissociated ones or the original molecules. The value of α for a strong electrolyte is nearly 1. On the other hand, for a weak electrolyte it is less than 1, when it is under normal dilution.