Final answer:
The statement is true; UV-vis spectroscopy is used for both qualitative identification of molecules and quantitative analysis in organic and biological chemistry, following the Beer - Lambert Law for concentration measurements.
Step-by-step explanation:
The statement True or False: UV-vis is used both qualitatively and quantitatively is true. UV-vis (ultraviolet-visible) spectroscopy is a versatile analytical technique widely applied in organic and biological chemistry. It can be used to qualitatively identify molecules by observing their spectra in the ultraviolet and visible regions, particularly for molecules with conjugated systems. This is because these molecules exhibit characteristic absorption patterns, with chromophores absorbing at specific wavelengths based on the nature of their electronic transitions. Qualitative analysis may involve determining the color of the compound, as for example, a compound with maximum absorbance at 630 nm in the orange range would appear blue due to complementary color perception.
UV-vis spectroscopy is equally important for quantitative analysis, as it follows the Beer - Lambert Law. This law states that within certain limits, the absorbance at a given wavelength is proportional to the concentration of the chromophore, enabling accurate quantification. Examples include measuring the concentration of DNA using a Nanodrop spectrometer, where absorbance at 260 nm is used as an indicator of DNA quantity. Therefore, UV-vis spectroscopy can provide both a description of the quality (qualitative) and the specific amount (quantitative) of a substance, making it a critical tool in scientific research.