Colligative Properties

Concept: In colloidal chemistry, protective colloids are lyophilic colloids that prevent the coagulation of lyophobic sols by forming a protective layer around dispersed particles. The effectiveness of a protective colloid is measured using the Gold Number. Definition of Gold Number: Gold number is defined as the minimum mass (in milligrams) of a protective colloid required to prevent the coagulation of 10 mL of a standard gold sol when 1 mL of 10% sodium chloride solution is added.
Explanation: When an electrolyte like NaCl is added to a gold sol, the colloidal particles tend to coagulate. A protective colloid adsorbs onto the surface of gold particles and stabilizes them by:

• Providing a protective layer
• Preventing particle aggregation
• Enhancing colloidal stability

Significance of Gold Number:

• Measure of protective power: It indicates the efficiency of a protective colloid.
• Inverse relationship: Lower gold number means higher protective power.
• Comparison tool: Used to compare different protective colloids (e.g., gelatin vs starch).
• Industrial relevance: Important in pharmaceuticals, paints, and food industries where colloidal stability is essential.

Conclusion: Thus, the gold number is a quantitative measure of the protective ability of a colloid, with smaller values indicating better protection against coagulation.

Concept: Raoult's law describes the relationship between the vapor pressure of a solvent and the presence of a solute in a solution. It is especially applicable to dilute solutions and ideal solutions. Statement: For a solution containing a non-volatile solute, Raoult's law states that: \begin{quote} The vapor pressure of the solvent over the solution is directly proportional to the mole fraction of the solvent present in the solution. \end{quote} Mathematically, where:

• = vapor pressure of the solvent in the solution
• = vapor pressure of the pure solvent
• = mole fraction of the solvent

Since the solute is non-volatile, it does not contribute to vapor pressure. Its presence lowers the vapor pressure of the solvent compared to the pure solvent. Conclusion: Thus, in a solution containing a non-volatile solute, the vapor pressure of the solvent decreases in proportion to the mole fraction of the solvent.