Question

When \(\mathrm{NaCl}\) is added to the reaction mixture of an oil and caustic soda, the soap is thrown out because (1) \(\mathrm{NaCl}\) is an ionic compound (2) Soap is insoluble in the presence of chloride ions (3) The solubility product of \(\mathrm{NaCl}\) decreases in the presence of soap (4) The solubility product of the soap is excceded duc to the increased concentration of \(\mathrm{Na}^{-}\) ions

Short answer

The solubility product of the soap is exceeded due to the increased concentration of \(Na^+\) ions (Option 4).

Step-by-step solution

- Understand the reaction

The reaction involves the addition of \(\text{NaCl}\) to a mixture of oil and caustic soda (NaOH), resulting in the formation of soap.

- Identify the components produced

\(\text{NaCl}\) is composed of sodium ions (\(\text{Na}^+\)) and chloride ions (\(\text{Cl}^-\)). When added to the reaction mixture, it dissociates into these ions.

- Examine the role of sodium ions

The sodium ions (\(\text{Na}^+\)) will interact with the soap molecules in the mixture.

- Effect of ionic interaction on soap solubility

When the concentration of \(Na^+\) ions increases due to the addition of \(\text{NaCl}\), the solubility product of the soap exceeds. This causes the soap to precipitate out of the solution as it becomes less soluble.

Conclusion

The correct reason for the precipitation of soap is that the solubility product of the soap is exceeded due to the increased concentration of \(Na^+\) ions.

Key concepts

Ionic Interaction

Ionic interactions are fundamental in the world of chemistry. They involve positive and negative ions attracting each other.
When \(\text{NaCl}\) (table salt) is added to a mixture like the one described in the exercise, it dissociates into \(\text{Na}^+\) (sodium ions) and \(\text{Cl}^-\) (chloride ions).
These ions don't just float around aimlessly. They interact with other charged particles in the mixture. Imagine sodium ions acting like tiny magnets, seeking out negatively charged particles or polar molecules to bond with.
In the soap-making reaction, the added sodium ions cause the soap molecules to aggregate more tightly, making them less soluble in water. Remember, ionic interactions can drastically alter the properties of the substances in a mixture.

Solubility Product

The solubility product (Ksp) is an equilibrium constant that helps us understand the solubility of ionic compounds.
In simpler terms, Ksp tells us how much ionic compound can dissolve in a solution before it starts to precipitate out (form a solid).
When \(\text{NaCl}\) is added to the mixture, the concentration of \(\text{Na}^+\) ions increases significantly. This change affects the solubility product of the soap.
Soap is an ionic compound, and its precipitation is governed by its solubility product. As the \(\text{Na}^+\) concentration rises, the product of the ion's concentrations hits the Ksp threshold. When this limit is exceeded, the ions can't stay dissolved, leading to the soap precipitating out of the solution.

Sodium Ions Effect

Sodium ions (\text{Na}^+) play a crucial role in the precipitation of soap. Let's break it down in more detail:

• When \(\text{NaCl}\) is added, it dissolves, and \(\text{Na}^+\) ions are released into the solution.
• These \(\text{Na}^+\) ions increase the overall ion concentration in the reaction mixture.
• This increase in sodium ions impacts the solubility of the soap, which is another ionic compound.
• Due to the higher concentration of sodium ions, the solubility product (Ksp) for soap is exceeded.

As a result of this effect, the soap molecules are no longer able to stay dissolved, causing them to precipitate out.
In essence, the addition of sodium ions from \(\text{NaCl}\) modifies the reaction environment, leading to the precipitation of soap.