The substance that turns red when mixed with sodium chloride is phenolphthalein. Phenolphthalein is an organic compound that is colorless in its neutral form but turns pink or red in an alkaline environment. When sodium chloride, which is commonly known as table salt, is dissolved in water, it dissociates into sodium and chloride ions. These ions do not affect the color of phenolphthalein directly. However, when an alkali, such as sodium hydroxide, is added to the solution, the hydroxide ions react with the sodium ions, forming sodium hydroxide, which is a strong base. This increase in pH causes the phenolphthalein to change color from colorless to pink or red.

The color change is a result of the chemical structure of phenolphthalein. In its neutral form, the molecule has a planar structure with a hydrogen bond between the oxygen atom of the carboxyl group and the oxygen atom of the phthalhydrazide group. When the pH increases, the hydrogen bond is broken, and the molecule adopts a non-planar structure, which allows it to absorb light at a different wavelength, resulting in the red color. This pH range for the color change is typically between 8.2 and 10.0.

The phenomenon is widely used in chemistry for titrations, where a known concentration of an acid or base is used to determine the concentration of an unknown substance. For example, in acid-base titrations, phenolphthalein is often used as an indicator to signal the endpoint of the reaction. The sharp color change from colorless to pink or red is a clear and visible indicator that the reaction has reached its endpoint.

Data supporting the pH range for the color change of phenolphthalein can be found in various chemistry textbooks and scientific literature. For instance, according to "Principles of Instrumental Analysis" by Douglas A. Skoog, F. James Holler, and Stanley R. Crouch, the pH range for the color change of phenolphthalein is between 8.2 and 10.0 (Skoog et al., 2004). This information is crucial for accurate and reliable chemical analysis.