Question

The sol formed in the following unbalanced equation is:
\[ As_2O_3 + H_2S \rightarrow \]

• A. \(As_2S_2\)
• B. \(As_2S_3\)
• C. \(As\)
• D. \(S\)

Hint:

Arsenic sulfide sol \((As_2S_3)\) is a common example of a lyophobic colloid prepared by double decomposition reaction.

Answer 1

The Correct Option is B

Step 1: Write the reaction of arsenic trioxide with hydrogen sulfide.
When As₂O₃ reacts with H₂S in acidic solution: \[ As_2O_3 + 3H_2S \rightarrow As_2S_3 + 3H_2O \]
Step 2: Identify the product and its nature.
As₂S₃ (arsenic trisulfide) is a yellow solid that is insoluble in water. When formed from dilute solutions, it does not precipitate immediately but forms a colloidal dispersion.
Step 3: Explain the colloidal sol formation.
As₂S₃ particles formed in this reaction are extremely small (1-100 nm range). They remain dispersed in water as a colloidal sol due to adsorption of H₂S on their surface (stabilization by the excess reagent), creating a negatively charged colloidal sol.
Step 4: Classify the colloid type.
As₂S₃ sol is a lyophobic (solvent-hating) colloid. The dispersion medium is water, and As₂S₃ forms the dispersed phase. The sol is negatively charged (H₂S adsorbed on particles releases H⁺, leaving S^2- on the surface).
Step 5: Confirm this is a sol (colloidal solution).
A sol is a colloidal dispersion of a solid in a liquid. As₂S₃ in water = As₂S₃ sol - fits perfectly.
Step 6: Final answer.
The product formed is As₂S₃ (arsenic trisulfide sol), a negatively charged lyophobic colloidal sol.
\[ \boxed{As_2S_3 \text{ sol (option 2)}} \]