Question

$\mathrm{KF}$ is a strong electrolyte, and $\mathrm{HF}$ is a weak electrolyte. How does their dissociation in water differ?

Short answer

KF completely dissociates in water, whereas HF only partially dissociates.

Step-by-step solution

Understand Electrolytes

Electrolytes are substances that conduct electricity when in aqueous solution. They dissociate into ions.

Identify Strong and Weak Electrolytes

A strong electrolyte, like $\text{KF}$, completely dissociates into its ions in water. A weak electrolyte, like $\text{HF}$, only partially dissociates into its ions.

Write the Dissociation Equations

The dissociation of a strong electrolyte, $\text{KF}$, is given by: $$\text{KF}\to {\text{K}}^{+}+{\text{F}}^{-}$$ The dissociation of a weak electrolyte, $\text{HF}$, is given by: $$\text{HF}\rightleftharpoons {\text{H}}^{+}+{\text{F}}^{-}$$

Compare the Degree of Dissociation

Since $\text{KF}$ completely dissociates, all of it turns into ${\text{K}}^{+}$ and ${\text{F}}^{-}$ ions. In contrast, because $\text{HF}$ is a weak electrolyte, only a small fraction of $\text{HF}$ will dissociate into ${\text{H}}^{+}$ and ${\text{F}}^{-}$ ions. Most of the $\text{HF}$ remains as undissociated molecules.

Key concepts

Strong Electrolytes

Strong electrolytes are compounds that completely dissociate into ions when dissolved in water.
This means that every molecule of the electrolyte separates into its respective ions.
For example, when potassium fluoride (KF) is added to water, it fully breaks down into potassium ions (K\textsuperscript{+}) and fluoride ions (F\textsuperscript{-}).
As a result, the solution becomes a good conductor of electricity.
The dissociation equation for KF in water can be written as:
$$\text{KF}\to {\text{K}}^{+}+{\text{F}}^{-}$$
Strong electrolytes include most salts, strong acids, and strong bases.
Their complete dissociation ensures that there are plenty of ions available to carry electric current.

Weak Electrolytes

Weak electrolytes, unlike strong electrolytes, only partially dissociate in water.
This means that only a small fraction of the molecules break down into ions, while the rest remain as intact molecules.
An example is hydrofluoric acid (HF), which only slightly dissociates into hydrogen ions (H\textsuperscript{+}) and fluoride ions (F\textsuperscript{-}).
The partial dissociation leads to a solution that is a relatively poor conductor of electricity.
The dissociation equation for HF in water is:
$$\text{HF}\rightleftharpoons {\text{H}}^{+}+{\text{F}}^{-}$$
Examples of weak electrolytes include weak acids and weak bases.
Their degree of dissociation is influenced by factors such as concentration and temperature.

Dissociation in Water

Dissociation in water refers to the process of molecules or compounds breaking down into ions when they are dissolved.
This process varies between strong and weak electrolytes. Strong electrolytes, like salts and strong acids, fully dissociate in water. This full dissociation provides many ions in the solution, which can conduct electricity well.
Weak electrolytes partially dissociate, thus producing fewer ions. This partial dissociation makes the solution a poor conductor of electricity.
Dissociation is essential in chemical reactions, especially those in biological systems and industrial applications.
Dissociation is often represented using chemical equations where a single-headed arrow denotes complete dissociation, while a double-headed arrow indicates partial dissociation.
The nature of the electrolyte and conditions such as temperature and concentration significantly impact the degree of dissociation.

Degree of Dissociation

The degree of dissociation measures the extent to which an electrolyte breaks down into ions in solution.
In the case of strong electrolytes, this degree is 100%, meaning complete dissociation.
Weak electrolytes have a degree of dissociation less than 100%, often much lower.
For example, if we dissolve HF in water, only a small portion of HF molecules will convert into H\textsuperscript{+} and F\textsuperscript{-} ions.
Most HF molecules remain intact as neutral molecules.
The degree of dissociation ($\text{α}$) is calculated using the formula:
$$\text{α}=\frac{\text{number of dissociated molecules}}{\text{total number of molecules}}$$
A higher degree means stronger electrolyte properties and better conductivity.
Several factors affect the degree of dissociation, including the nature of the electrolyte, solvent properties, temperature, and concentration.
Understanding the degree of dissociation helps predict the behavior of electrolytes in various chemical reactions and processes.