How do you find specific rotation of sugar solution using bi-quartz polarimeter?

Answer 1

Take a sample of inactive solvent say tap water(400 ml).Switch on the light source of the polarimeter.

1. Fill the polarimeter tube with it there should not be any air bubble left in the tube. Rotate the knob (that controls the movement of nicol prism analyser)in clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
2. Record the readings in both sides of the vernier scale.
3. Rotate the knob (that controls the movement of nicol prism analyser)in anti-clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
4. Again, record the readings in both sides of the vernier scale.

Preparing the sugar solution of required concentration weight by weight.

• 10% sugar solution is prepared by adding 10 gram sugar to 80 ml water and making final volume of the solution so formed to 100 ml.

1. Fill the polarimeter tube with 10% sugar solution ,there should not be any air bubble left in the tube. Rotate the knob (that controls the movement of nicol prism analyser)in clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
2. Record the readings in both sides of the vernier scale.
3. Rotate the knob (that controls the movement of nicol prism analyser)in anti-clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
4. Again, record the readings in both sides of the vernier scale.

Subtract:

1. the clockwise reading for tap water from the clockwise reading recorded for 10% sugar solution .
2. the anti-clockwise reading for tap water from the anti-clockwise reading recorded for 10% sugar solution .

Add the results obtained from step 1 and step 2 of the subtract operation and divide by 2. this gives the average value of angular rotation produced by sugar component alone for 10% concentration.

• 5% sugar solution is prepared by adding 5 gram sugar to 80 ml water and making final volume of the solution so formed to 100 ml.

1. Fill the polarimeter tube with 5% sugar solution ,there should not be any air bubble left in the tube. Rotate the knob (that controls the movement of nicol prism analyser)in clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
2. Record the readings in both sides of the vernier scale.
3. Rotate the knob (that controls the movement of nicol prism analyser)in anti-clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
4. Again, record the readings in both sides of the vernier scale.

Subtract:

1. the clockwise reading for tap water from the clockwise reading recorded for 5% sugar solution .
2. the anti-clockwise reading for tap water from the anti-clockwise reading recorded for 5% sugar solution .

Add the results obtained from step 1 and step 2 of the subtract operation and divide by 2. this gives the average value of angular rotation produced by sugar component alone for 5% concentration.

• 2.5% sugar solution is prepared by adding 2.5 gram sugar to 80 ml water and making final volume of the solution so formed to 100 ml.

1. Fill the polarimeter tube with 2.5% sugar solution ,there should not be any air bubble left in the tube. Rotate the knob (that controls the movement of nicol prism analyser)in clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
2. Record the readings in both sides of the vernier scale.
3. Rotate the knob (that controls the movement of nicol prism analyser)in anti-clockwise direction until you get a critical region in which illumination of the central band as observed from the eyepiece changes from slight brightness to complete darkness or vice-versa.
4. Again, record the readings in both sides of the vernier scale.

Subtract:

1. the clockwise reading for tap water from the clockwise reading recorded for 2.5% sugar solution .
2. the anti-clockwise reading for tap water from the anti-clockwise reading recorded for 2.5% sugar solution .

Add the results obtained from step 1 and step 2 of the subtract operation and divide by 2. this gives the average value of angular rotation produced by sugar component alone for 2.5% concentration.

TO CALCULATE THE SPECIFIC ROTATION OF THE CANE-SUGAR .

• Plot the graph with concentration on x-axis and angular rotation produced by sugar component alone for different concentrations taken on y-axis.
• slope of the straight line so obtained on the graph divided by length of polarimeter tube gives the specific rotation of the cane sugar.
• note the temperature at which experiment is performed.

Answer 2

The specific rotation of a chemical compound [α] is defined as the observed angle of optical rotation α when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample concentration of 1 gram per 1 millilitre. The specific rotation of a pure material is an intrinsic property of that material at a given wavelength and temperature. Values should always be accompanied by the temperature at which the measurement was performed and the solvent in which the material was dissolved. Often the temperature is not specified; in these cases it is assumed to be room temperature. The formal unit for specific rotation values is deg dm-1cm3 g-1 but scientific literature uses just degrees. A negative value means levorotatory rotation and a positive value means dextrorotatory rotation. Some examples:

• Sucrose +66.47°

Optical rotation is measured with an instrument called a polarimeter. There is a linear relationship between the observed rotation and the concentration of optically active compound in the sample. There is a non-linear relationship between the observed rotation and the wavelength of light used. Specific rotation is calculated using either of two equations, depending on the sample you are measuring:

For pure liquids:

In this equation, l is the path length in decimeters, and d is the density of the liquid in g/mL, for a sample at a temperature T (given in degrees Celsius) and wavelength λ (in nanometers). If the wavelength of the light used is 589 nanometer (the sodium D line), the symbol "D" is used. The sign of the rotation (+ or -) is always given.°

For solutions, a different equation is used:

In this equation, l is the path length in decimeters and c is the concentration in g/100mL, for a sample at a temperature T (given in degrees Celsius) and wavelength λ (in nanometers). If the wavelength of the light used is 589 nanometer (the sodium D line), the symbol "D" is used. The sign of the rotation (+ or -) is always given. When using this equation, the concentration and the solvent are always provided in parentheses after the rotation. The rotation is reported using degrees, and no units of concentration are given (it is assumed to be g/100mL).

Answer 3

To find the specific rotation of a sugar solution using a bi-quartz polarimeter, you will need to measure the angle of rotation of polarized light passing through the solution. This angle is then used to calculate the specific rotation using the formula: [α] = observed rotation / (concentration of solution * path length). Make sure to follow proper calibration and measurement procedures for accurate results.

Answer 4

1024