[PHA6113 lab] Activity 5: Optical Activity

Question 1

Property of substances to rotate the plane of polarization to the polarized light

Answer 1

Optical Activity

Question 2

What USP number is Optical Activity?

Answer 2

<781>

Question 3

[Characteristics]
T or F: Molecules should be superimposable

Answer 3

False, should not be superimposable (disymmetric)

Question 4

[Characteristics]
T or F: There should be a presence of a chiral carbon

Answer 4

True

Question 5

A carbon that has 4 different molecules attached to it

Answer 5

Chiral carbon

Question 6

What do you call the rotation for liquids?

Answer 6

Optical rotation

Question 7

What do you call the rotation for solids or substances in a solution?

Answer 7

Specific rotation

Question 8

What instrument is used for taking optical activity?

Answer 8

Polarimeter

Question 9

Different types of Polarimeter

Answer 9

Visual and Photoelectric

Question 10

General parts of a Polarimeter

Answer 10

Light source, Polarizer, Analyzer

Question 11

This holds the sample inside a polarimeter

Answer 11

Sample tube or Polarimeter tube

Question 12

<781A>

Answer 12

Determination of Angular Rotation

Question 13

Symbol used for Angular Rotation

Answer 13

a (alpha)

Question 14

The optical rotation of the neat liquid is measured in a ___________

Answer 14

1.0-dm tube at 589nm at 25 degrees (unless otherwise stated)

Question 15

Laboratory Procedure for Determination of Angular Rotation

Answer 15

> Turn on light source
Rotate analyzer until tripartite field becomes equal in intensity
Rinse the polarimeter tube with distilled water then fill to the top (overflow)
Tighten the screw caps carefully - not too tight and not too loose to prevent double refraction under pressure
Place the tube in the polarimeter and rotate the analyzer until the field is equally illuminated – Make 1 reading of this blank

Question 16

[Interpretation]
Dextrorotatory

Answer 16

(+) - clockwise

Question 17

[Interpretation]
Levorotatory

Answer 17

(-) - counterclockwise

Question 18

When there is an equal portion of both levo and dextro, what is it called?

Answer 18

Racemic Mixture

Question 19

REMEMBER

Answer 19

Do readings clockwise
Do readings counterclockwise
Compare and the lesser one will be used

Question 20

HOW TO READ A POLARIMETER

Answer 20

PRACTICE READINGS FROM THE PPT

Question 21

[Determination of Angular Rotation]
What is the general equation?

Answer 21

a solute = a solution - a solvent

Question 22

[Determination of Angular Rotation]
When there are different signs, what is the rule?

Answer 22

Add then take the sign of the larger value

Question 23

[Determination of Angular Rotation]
When there are same signs, what is the rule?

Answer 23

Subtract and copy the sign

Question 24

Angle through which the plane of polarization of light is rotated when polarized light passes through a 1dm layer of the liquid at a specified temperature

Answer 24

Specific Rotation

Question 25

<781S>

Answer 25

Specific Rotation

Question 26

Symbol for Specific Rotation

Answer 26

[a]^t_y

Question 27

T or F: Measurements for Specific rotation is the same with optical rotation

Answer 27

True –> 1.0-dm tube at 589nm at 25 degrees

Question 28

Formula for Specific or Optical Rotation

Answer 28

[a]^t_y = a/lc
where; a - angular rotation
l - length of the tube
c - concentration (solids or solutions); density (liquids)

Question 29

Rotation of plane polarized light occurs at a ____________, so the extent of the rotation is ___________ to the amount of optically active material

Answer 29

Molecular level, proportional

Question 30

[Determination of Molar Rotation]
Formula of Molar Rotation

Answer 30

[o] = ([a]^t_y x MW) / 100

Question 31

PRACTICE PROBLEMS

Answer 31

PRACTICE USING PPT