Colloids

Step 1: Understanding colloids.
Colloids are classified into two categories based on the interaction of dispersed phase with dispersion medium: lyophilic (solvent-loving) and lyophobic (solvent-hating).
Step 2: Differences.
\begin{tabular}{|c|c|c|} \hline Property &
Lyophilic Colloids &
Lyophobic Colloids
\hline Affinity for medium & High affinity for dispersion medium & Little or no affinity for medium
\hline Stability & Very stable and not easily coagulated & Unstable and easily coagulated
\hline Reversibility & Reversible sols & Irreversible sols
\hline Examples & Starch sol, Gum, Gelatin & Gold sol, Sulphur sol, As S sol
\hline Preparation & Form spontaneously & Require special methods
\hline \end{tabular} Conclusion:
Lyophilic colloids are stable and reversible due to strong attraction for solvent, while lyophobic colloids are unstable, irreversible and need stabilizers for existence.

Step 1: Understanding colloids.
Colloids are heterogeneous systems where one substance is dispersed in another. Based on affinity between dispersed phase and dispersion medium, colloids are of two types – lyophilic and lyophobic.
Step 2: Key differences.
\begin{tabular}{|c|c|c|} \hline Property &
Lyophilic Colloids &
Lyophobic Colloids
\hline Affinity & High affinity for dispersion medium & Little/no affinity for dispersion medium
\hline Stability & Very stable & Less stable, easily coagulated
\hline Reversibility & Reversible sols & Irreversible sols
\hline Examples & Starch, proteins, gum & Gold sol, sulphur sol, As S sol
\hline Preparation & Form spontaneously & Need special methods
\hline \end{tabular} Conclusion:
Lyophilic colloids are stable and reversible due to high affinity with solvent, while lyophobic colloids are unstable and need stabilizing agents.

(i) The colloidal solution of Fe(OH) obtained from FeCl is positively charged:
When FeCl is hydrolyzed, Fe(OH) sol is formed. The Fe ions from FeCl get adsorbed on the surface of Fe(OH) particles.
This leads to the development of a positive charge on the colloidal particles. Hence, the sol of Fe(OH) is positively charged. (ii) Alum is used for the purification of water:
Alum (K SO Al (SO ) 24H O) produces Al ions in water. These ions neutralize the negative charges on colloidal impurities present in water.
As a result, the colloidal particles coagulate, settle down, and can be easily removed. Hence, alum acts as a coagulant in water purification. (iii) Rivers form a delta while joining a sea/ocean:
Rivers carry colloidal particles like clay and silt. When river water meets sea water (which contains electrolytes like NaCl, MgCl ), the electrolytes coagulate the colloidal particles.
These coagulated particles settle at the river mouth, gradually forming delta regions. Conclusion:
The above examples demonstrate the role of adsorption and coagulation in colloidal chemistry and natural phenomena.