What property does a polarimeter measure?

What property does a polarimeter measure?

• A. Refractive index
• B. Absorbance
• C. Optical rotation
• D. Density

Answer: (C)

A polarimeter measures optical rotation—the rotation of the plane of polarization that light experiences as it passes through a chiral (optically active) substance. In practice, plane-polarized light is produced, passes through a sample in a cell, and an analyzer determines the angle at which transmitted light is maximum. That angle is the observed optical rotation, usually reported in degrees. Optical rotation depends on the substance’s concentration and path length (captured in the specific rotation, [α] = α/(l c)) and on the light’s wavelength. The sign of the rotation tells whether the substance is dextrorotatory or levorotatory. In contrast, refractive index, absorbance, and density are measured with other instruments (refractometer, spectrophotometer, and density meter, respectively).

A polarimeter measures optical rotation—the rotation of the plane of polarization that light experiences as it passes through a chiral (optically active) substance. In practice, plane-polarized light is produced, passes through a sample in a cell, and an analyzer determines the angle at which transmitted light is maximum. That angle is the observed optical rotation, usually reported in degrees. Optical rotation depends on the substance’s concentration and path length (captured in the specific rotation, [α] = α/(l c)) and on the light’s wavelength. The sign of the rotation tells whether the substance is dextrorotatory or levorotatory. In contrast, refractive index, absorbance, and density are measured with other instruments (refractometer, spectrophotometer, and density meter, respectively).