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How can turbidity indicate that a reaction is complete?

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combustion — chemical reaction Log burning in a fire. Burning wood is an example of a chemical reaction in which wood in the presence of heat and oxygen is transformed into carbon dioxide, water vapor, and ash.

In chemistry, turbidity can serve as a visual indicator to signal the completion of a reaction, often referred to as the end point. While many indicators signal completion through color changes, some reactions rely on the formation or disappearance of suspended particles that create a cloudy appearance.12

A reaction reaches its end point when the concentration of a specific chemical species reaches a critical threshold. For example, when a soluble silver salt is added to a solution containing cyanide and a trace of iodide, the solution remains clear as long as the cyanide is reacting to form a soluble complex. Once all the cyanide has been consumed, the addition of further silver causes the formation of insoluble silver iodide, resulting in visible turbidity. In this instance, the iodide acts as an indicator for the presence of excess silver ions, marking the completion of the primary reaction.1

The degree of such cloudiness can be analyzed using turbidimetry, a method that measures the intensity of light transmitted through a sample to determine the concentration of suspended material.2