Step 1: Understanding the Concept:
Colloidal particles naturally carry an electrical charge, which can be positive or negative depending on the chemical nature of the dispersed phase and the specific method of preparation. We need to classify the given sols based on their standard accepted charge.
Step 2: Key Formula or Approach:
Approach: Classify the given colloidal sols based on standard charge conventions for basic/acidic components, metal sulfides, and biological macromolecules.
Step 3: Detailed Explanation:
Let's review the classification of common textbook sols based on their charge:
- Positively charged sols: Metallic hydroxides [like $\text{Fe(OH)}_3$, $\text{Al(OH)}_3$], basic dyes (like methylene blue), and biologically important basic macromolecules like haemoglobin in blood.
- Negatively charged sols: Metal sols (like $\text{Cu}$, $\text{Ag}$, $\text{Au}$), metallic sulfides (like $\text{As_2\text{S}_3$}, $\text{Sb}_2\text{S}_3$), acid dyes (like eosin, Congo red), and naturally occurring sols like starch, gum, gelatin, and clay.
Based strictly on this standard classification:
- $\text{As}_2\text{S}_3$ is a well-known negatively charged sol.
- Clay is a naturally occurring negatively charged sol.
- Congo Red is an acidic dye, hence it forms a negatively charged sol.
- Haemoglobin is a widely cited example of a positively charged macromolecular sol.
Step 4: Final Answer:
Haemoglobin is not a negatively charged sol; it is positively charged.