How does colorimetric testing determine the presence of a substance?

Colorimetric testing is a method that qualitatively or quantitatively determines the presence of a substance based on color changes that occur during a chemical reaction. When a sample is tested, specific reagents are added that react with the target substance, producing a color change that correlates with its concentration. The intensity of the resulting color can then be measured using colorimetric instruments to provide a precise indication of the amount of the substance present. This method is widely utilized in forensic science for analyzing various substances, such as drugs, toxins, or biological markers, because it offers a clear and rapid visual result that is easy to interpret.

The other options do not align with the fundamental principle of colorimetric testing. Measuring the weight of a sample does not provide information about its chemical composition, while the analysis of sound frequencies pertains to different analytical techniques like spectroscopy. Infrared spectroscopy involves examining the interaction of infrared light with matter, which is not based on color change but rather on the absorption of specific wavelengths by molecular bonds.