Inversion of Sucrose by Digital Polarimeter

Inversion of Sucrose by Polarimeter Aim:

 To determine the specific rotation of sucrose at different concentrations. Apparatus: 1.

Polarimeter

2.

Sodium vapour lamp

3.

Five 100 ml standard flasks

Chemical required:

Sucrose, Distilled water. Principle:

Ordinary light has vibration in all the possible directions, whereas plane polarized light has vibration in only one direction. If an unpolarised light is passed through a nicol prism, the emerging light is plane polarized.

If this light is passed through an optical active substance solution present in a sample tube, the plane of the polarized light waves is rotated. The rotation is noticed by looking through the analyser as a change in intensity of illumination. To reach the same illumination as in the case of without an optical active sample the analyser (The nicol prism, which is paned with axis 90 0 rotated) must be turned around for an angle. Readings are taken in degrees (angle) α. Procedure:

Set up a sodium vapour lamp at a distance equal to the focal length of the lens from the end of the polarimeter. Adjust the height of the lamp and optical axis of the instrument for maximum illumination of the polarizer. Take a properly cleaned polarimeter tube. Fill the tube with solutions whose optical activity is to be measured. Avoid air bubbles in the tube. There should be no liquid drops on the outside of the glass plate windows. Place the tube between the two nicol prisms now look through the eye piece. Rotate the analyser until the two halves of the field of  view as equally dark . The reading on the scale is read through the scale eye piece. If this reading is not exactly zero, an adjustment may be made in the instrument. Solution of 5 %, 7.5 %, 10 %, 15 % and 20 % are made and the optical rotation is calculated for each of them. Calculations:

Length of polarimeter tube (l) = __________ dm S.N o

% concentration of solution (C) (in g per 100 ml)

Angle of  rotation (α)

Specific rotation

1

20

2

15

3

10

4

7.5

5

5 Calculate the specific rotation by using the formula

Where

α = observed angle of rotation l = length of polarimeter tube (dm) C = Concentration of solution (g/ml)

Graph:

Draw the graph between concentration of sucrose solution (on Xaxis) and angle of the rotation (on Y-axis).Find the slope and calculate the specific rotation by using the formula,

Result:

 The specific rotation of the sucrose solution = _________ deg dm –1 g–1 ml

Precautions: (No need to write in record book)

1. Make sure no air bubble is trapped in the path of light. 2. When the experiment is over, the solution used is removed from the polarimeter tube and the tube is washed well with distilled water and dried before being stored. The caps are unscrewed, or at least loosened, before storing.