Colloids

Step 1: Precipitation of AgI.
When silver nitrate ( ) solution is added to excess potassium iodide ( ) solution, silver iodide ( ) precipitates out according to the following reaction:
Step 2: Formation of colloidal particles.
The precipitate formed, , can form colloidal particles in the presence of excess . Due to the presence of excess iodide ions ( ), these particles will be negatively charged.
Step 3: Conclusion.
Thus, the colloidal particles formed are negatively charged .