The stability of lyophobic colloids is significantly affected by the pH of the surrounding medium. Lyophobic colloids, also known as hydrophobic colloids, are colloidal systems in which the dispersed phase has little to no affinity for the dispersion medium. Examples of lyophobic colloids include sols of metals, metal sulfides, and certain organic compounds.The effect of pH on the stability of lyophobic colloids can be explained through the following factors:1. Charge on colloidal particles: The stability of lyophobic colloids is primarily due to the presence of charges on the surface of the colloidal particles. These charges create a repulsive force between particles, preventing them from aggregating and precipitating. The pH of the medium can affect the charge on the colloidal particles, and hence, their stability. For example, in the case of metal hydroxide sols, increasing the pH can lead to the formation of negatively charged particles, which can enhance the stability of the colloid.2. Solubility of the dispersed phase: The solubility of the dispersed phase in the dispersion medium is another factor that influences the stability of lyophobic colloids. The pH of the medium can affect the solubility of the dispersed phase, and hence, the stability of the colloid. For instance, the solubility of metal sulfides decreases with increasing pH, which can lead to the precipitation of the colloidal particles and destabilization of the colloid.Experimental data supporting the effect of pH on the stability of lyophobic colloids:A classic example of the effect of pH on the stability of lyophobic colloids is the gold sol. In acidic conditions low pH , gold sol particles carry a positive charge and repel each other, maintaining the stability of the colloid. However, when the pH is increased, the gold sol particles lose their positive charge, leading to a decrease in repulsive forces and subsequent aggregation and precipitation of the particles.Another example is the sol of ferric hydroxide. At low pH, the sol is positively charged and stable due to repulsive forces between the particles. As the pH is increased, the sol becomes negatively charged, and the stability is maintained. However, at very high pH, the solubility of ferric hydroxide decreases, leading to the precipitation of the colloidal particles and destabilization of the colloid.In conclusion, the pH of the surrounding medium plays a crucial role in determining the stability of lyophobic colloids. Changes in pH can affect the charge on the colloidal particles and the solubility of the dispersed phase, which in turn influence the stability of the colloid.