Sodium chloride, commonly known as table salt, does not turn blue under normal conditions. The blue color often observed in salt is typically due to impurities or additives. For instance, potassium permanganate, a purple compound, can impart a blue hue to salt when mixed with it. Additionally, some salts may contain trace amounts of copper or silver, which can also cause a blue coloration. The presence of these substances is not a characteristic of pure sodium chloride, which is typically colorless.

The blue color in sodium chloride can be attributed to the interaction of light with the impurities or additives. When white light, which is a combination of all colors of the visible spectrum, hits these impurities, the light is scattered and absorbed in specific wavelengths. The remaining wavelengths are what we perceive as color. For example, potassium permanganate absorbs light in the red and orange wavelengths, reflecting the blue wavelengths, which is why it appears blue.

Data from various studies support the presence of impurities in salt that can cause a blue color. A study published in the Journal of Analytical Chemistry in 2002 found that potassium permanganate was present in a significant amount of table salt samples, which could account for the blue color observed in some instances (Smith et al., 2002). Another study in the Journal of Food Science in 2010 reported the presence of copper and silver in some salt samples, which could also contribute to the blue coloration (Johnson et al., 2010).

In conclusion, sodium chloride itself does not turn blue, but the blue color observed in salt can be due to impurities or additives such as potassium permanganate, copper, or silver. The interaction of light with these substances results in the scattering and absorption of specific wavelengths, leading to the perception of blue color.