The stability of a colloidal sol of Fe OH 3 is highly dependent on the pH of the solution. The solubility and aggregation behavior of Fe OH 3 particles are influenced by the pH due to the surface charge of the particles and the concentration of ions in the solution.At low pH values acidic conditions , the surface of Fe OH 3 particles becomes positively charged due to the adsorption of H+ ions. This leads to electrostatic repulsion between the particles, which prevents them from aggregating and keeps the sol stable.At high pH values alkaline conditions , the surface of Fe OH 3 particles becomes negatively charged due to the deprotonation of hydroxyl groups OH- on the surface. This also results in electrostatic repulsion between the particles, maintaining the stability of the sol.However, at the isoelectric point IEP , which is the pH at which the surface charge of the particles is neutral, the electrostatic repulsion between the particles is minimized. This allows the particles to aggregate and form larger clusters, leading to the destabilization and precipitation of the colloidal sol. For Fe OH 3, the IEP is typically around pH 8.Experimental evidence to support this can be obtained by preparing a series of Fe OH 3 sols with varying pH values and monitoring their stability over time. The stability can be assessed by measuring the turbidity or particle size distribution of the sols. The results would show that the sols are stable at low and high pH values, but unstable and prone to precipitation at the IEP.Additionally, zeta potential measurements can be performed to determine the surface charge of the Fe OH 3 particles at different pH values. These measurements would confirm the positive surface charge at low pH, negative surface charge at high pH, and neutral surface charge at the IEP, providing further evidence for the effect of pH on the stability of the Fe OH 3 colloidal sol.