TASK 2 - POLARIMETRY:
QUANTITATIVE EVALUATION OF SUCROSE

Polarimetry is a method of qualitative or quantitative analysis of optically active chemical agents that contain an asymmetric atom of carbon. It is based on measurement of rotation of the plane of linearly polarized light (while normal light oscillates in all directions, polarized light - only in one direction) when travelling through liquids, some solids, or gases. The polarized light can be got by passage of the normal light through a Nicol prism. According to direction of the rotation of polarized light we recognize dextrorotatory and laevorotatory (in living organisms) chemical agents.

The optic activity depends on:

• specific properties of the agent,
• thickness of the layer through which the light travels,
• wave-length of light,
• concentration of solution,
• temperature of solution, and
• density of solution.
  
  Except for the wave lenght or temperature, all items are directly proportional.

Specific rotation α is mearured in degrees:

(1)

D - wave lenght of sodium-spectrum (589 nm)
α - optical rotation in degrees
l - path lenght in decimetres (in our case = 1)
c - concentration of agent in 100 g of solution
ρ - density of solution

Polarimetry is used for qualitative or quantitative evaluation of optically active agents in research as well as in practice, e.g. in the sugar industry to measure syrup concentration, in chemistry to characterize substances in solution, in optical mineralogy to help to identify certain minerals in thin sections, in medicine for mesurement of sugar in urine or blood, proteins, steroids, vitamines, or alkaloids.

1. Fill the polarimetric tube with tested solution, close it, dry the closing glasses, and put the polarimetric tube into the body tube;
2. Turn the driver to the left, and find picture of the 1^st stopping (see figure);
3. Then turn the driver to the right, and find picture of the 2^nd stopping;
4. Afterwards turn the driver a little back until you find the picture filled with neutral grey, then read the result;

   1st stopping	neutral grey	2nd stopping

5. Read resulting value: Read on the right-hand scale. It consists of the inner and outer scales: "0" point of the inner scale points units on the outer scale; the bar of the inner scale that is just opposite to a bar on the outer scale points decimal places (value read on the inner scale). On the following figure the measured value is 1.30^o (always read on 2 decimal places).

   

1. Solutions: From the stock solution of 50% sucrose prepare the following solutions: 2.5; 5.0; 10.0; 15.0, and 20.0%, 50 ml each; for the calculation use the RULE OF THREE:
   
   

   RULE OF THREE

   E.g.: to prepare 2.5% solution from the stock solution (50%): 50% .............................. 50 ml 2.5% ............................. x ml consequently: (50 x 2.5) / 50 = 2.5 ml. To prepare 2.5% solution use 2.5 ml of the stock solution (50%) and supplement it up to 50 ml with deionized water.

   
   
2. Measurements: Measure all solutions of sucrose plus 3 unknown samples (I, II, and III), 5times each. Calculate the average value for each series of measurements;
3. Results: