Optical activity

Question 1

plane-polarised light is

Answer 1

monochromatic light that has oscillations in only one plane

Question 2

optically active substances rotate

Answer 2

the plane of polarisation of plane-polarised light

Question 3

unpolarised light has

Answer 3

oscillations in all planes at right angles to the direction of travel

Question 4

a polarimeter is

Answer 4

the apparatus used to measure the angle of rotation caused by a substance

Question 5

a polariser

Answer 5

is a material that converts unpolarised light into plane-polarised light

Question 6

an analyser is

Answer 6

a material that allows plane-polarised light to pass through it

Question 7

a racemic mixture is

Answer 7

an equimolar mixture of two enantiomers that has no optical activity

Question 8

describe the steps used to test the optical activity of a sample:

Answer 8

• a polariser, for example Polaroid, is placed in front of a monochromatic light source
• this light will be passed through a test tube containing some of the sample in solution
• if the substance is optically active, then the plane of polarisation will be rotated so that it is no longer vertical.
• a second filter, the analyser, is rotated to a position where the maximum light intensity can be seen. the angle of rotation is measured and is quoted as positive for a clockwise rotation and negative for an anticlockwise rotation