Specific Rotation by Polarimeter

(1)

EXPERIMENT NO. -3

Polarization of Light

OBJECT

OBJECT_{:: To find the specific rotation of cane- sugar solution by a polarimeter at}_{To find the specific rotation of cane- sugar solution by a polarimeter at}

room temperature, using half-shade / Bi-quartz device. room temperature, using half-shade / Bi-quartz device.

APPARATUS USED

APPARATUS USED_{:: A polarimeter, cane sugar, a physical balance, weight box,}_{A polarimeter, cane sugar, a physical balance, weight box,}

a measuring cylinder, a beaker and a source of light. a measuring cylinder, a beaker and a source of light. [Note:

[Note: Use monochromatic source for half-shade device and white light sourceUse monochromatic source for half-shade device and white light source for bi-quartz device.

for bi-quartz device.]]

FORMULA USED

FORMULA USED_{:: The specific rotation of cane- sugar solution is given by}_{The specific rotation of cane- sugar solution is given by}

S = θ / l.c = θ.V / l.m S = θ / l.c = θ.V / l.m Where

Where θθ == rotation produced in degrees,rotation produced in degrees, ll == length of the tube in decimetre,length of the tube in decimetre, m

m == mass of sugar in gms. Dissolved in water,mass of sugar in gms. Dissolved in water, V

V == volume of sugar solution in cc.volume of sugar solution in cc. c

c == concentration of cane-sugar solutionconcentration of cane-sugar solution = m/V= m/V

OBSERVATIONS OBSERVATIONS_::

Length

Length of of the the polarimeter polarimeter tube tube = = --- --- dm.dm. R

Roooom m tteemmppeerraattuurre e = = --- oo_C._C.

Mass

Mass of of the the paper paper = = ---gm.---gm. M

Maasss s oof f tthhe e ppaappeer r pplluus s ssuuggaarr = = ---ggmm.. M

Maasss s oof f tthhe e ssuuggaar r ttaakkeen n ‘‘mm’’ = = --- - ggmm.. V

Voolluumme e oof f tthhe e ssoolluuttiioon n ‘‘VV’’ = = ---cccc.. Concentration

(2)

OBSERVATION FOR THE ANGLE OF ROTATION OBSERVATION FOR THE ANGLE OF ROTATION_:-

:-Value of one division of the main scale (MS) = x Value of one division of the main scale (MS) = x Total no. of division on the vernier scale (VS) = y Total no. of division on the vernier scale (VS) = y Least count of instrument (LC) = x/y

Least count of instrument (LC) = x/y

Analyzer reading with pure water Analyzer reading with pure water

S. S. No. No. Conc. in gm /cc. Conc. in gm /cc. c=m/V c=m/V

Analyzer reading with solution Analyzer reading with solution

Angle of rotation Angle of rotation (θ) (θ) IIsst t ppoossiittiioonn 118800oo a

appaarrt t ppoossiittiioonn IIsst t ppoossiittiioonn 118800oo

apart position apart position ((aa) ) ==MMSS++VVSSxxLLCC ((bb) ) ==MMSS++VVSSxxLLC C ((cc) ) ==MMSS++VVSSxxLLCC ((dd) ) ==MMSS++VVSSxxLLCC Ist Ist position position e=a~c e=a~c 180 180oo_apart_apart f=b~d f=b~d Mean Mean θ =(e + f)/2 θ =(e + f)/2 1 1 _c_c₁₁ θθ11 2 2 _c_c₂₂ θθ22 3 3 _c_c₃₃ θθ33 3 3 -Ray diagram:

(3)

Ray diagram:

Ray diagram: (Should be on left page by pencil)(Should be on left page by pencil)

CALCULATIONS

CALCULATIONS_{:: (Should be on left page by pen)}_{(Should be on left page by pen)}

S

S11 = θ= θ11/ l.c/ l.c11 =…………; S=…………; S22 = θ= θ22/ l. c/ l. c22 =………….. =………….. ; ; SS33 = θ= θ33/ l. c/ l. c33 =………… ;=………… ;

S

S = = (S(S11 + S+ S22 + S+ S33) / 3) / 3

RESULTS

RESULTS_{:: The specific rotation for cane- sugar solution at ________}_{The specific rotation for cane- sugar solution at ________}00_{C is}_{C is}

_________ degree per dcm per unit concentration. _________ degree per dcm per unit concentration.

(4)

CALCULATION FOR MAXIMUM PROBABLE ERROR

CALCULATION FOR MAXIMUM PROBABLE ERROR _{:: (Should be on left page}_{(Should be on left page}

by pen) by pen)

S = θ/ l.c = θ.V/ l.m S = θ/ l.c = θ.V/ l.m

Taking log both side and differentiate Taking log both side and differentiate ΔS/S = Δ θ / θ + ΔV / V+ Δ l / l + Δ m/ m ΔS/S = Δ θ / θ + ΔV / V+ Δ l / l + Δ m/ m = …………. % = …………. % [Note: Δ θ = 0.1º, Δ V =0.1c.c, Δ l = 0.1cm, Δ m = 0.001gm] [Note: Δ θ = 0.1º, Δ V =0.1c.c, Δ l = 0.1cm, Δ m = 0.001gm]

SOURCES OF ERROR AND PRECAUTIONS: SOURCES OF ERROR AND PRECAUTIONS:

(i) End faces of the polarimeter tube should be cleaned and fitted air tight. (i) End faces of the polarimeter tube should be cleaned and fitted air tight. (ii) Water and the solution must be dust free.

(ii) Water and the solution must be dust free.

(iii) There should be no air bubble in the part of light through the polarimeter tube. (iii) There should be no air bubble in the part of light through the polarimeter tube. (iv) The tube should be well rinsed before filling it with the solution every time. (iv) The tube should be well rinsed before filling it with the solution every time.

PROCEDURE: PROCEDURE:

1.

1. The leThe least couast count of nt of vernier vernier attached attached to the to the instrumeinstrument is nt is determindetermined.ed.

2.

2. The eye piece attached to the analyzer is focused on the half-shade.The eye piece attached to the analyzer is focused on the half-shade.

3.

3. The polarimeter tube is then carefully cleaned and filled with water (takingThe polarimeter tube is then carefully cleaned and filled with water (taking care that no air bubble is enclosed in it). The tube is now placed at its proper care that no air bubble is enclosed in it). The tube is now placed at its proper place inside the polarimeter.

place inside the polarimeter.

4.

4. The The sosourcurce e of of liglight ht is is swiswitchtched ed onon. . LoLookoking ing thrthrouough gh ththe e teltelescescopope, e, thethe analyzer is rotated till the two half of the field of view are equally illuminated analyzer is rotated till the two half of the field of view are equally illuminated (in half-shade arrangement)). This position of the analyzer is noted by reading (in half-shade arrangement)). This position of the analyzer is noted by reading the main and vernier scales.

the main and vernier scales.

5.

5. A second position of equal illumination of the two half of the field of view (inA second position of equal illumination of the two half of the field of view (in half-shade), nearly 180

half-shade), nearly 18000

apart of the first position is also noted. apart of the first position is also noted.

(5)

6.

6. A solution of cane sugar of known strength is prepared (say by dissolving 5A solution of cane sugar of known strength is prepared (say by dissolving 5 gm of sugars in water till solution is 50 c.c.). The solution is kept in a beaker. gm of sugars in water till solution is 50 c.c.). The solution is kept in a beaker.

7.

7. The water of the polarimeter tube is then replaced by the sugar solution andThe water of the polarimeter tube is then replaced by the sugar solution and the analyzer is reset for equal brightness. Both the positions (1

the analyzer is reset for equal brightness. Both the positions (1 stst _{and 180º}_{and 180º}

apart) are found out by taking the readings of the main and vernier scales. apart) are found out by taking the readings of the main and vernier scales.

8.

8. The mean of the differences of the corresponding positions of the analyzer The mean of the differences of the corresponding positions of the analyzer (for water and solution) gives the angle of rotation produced by the solution. (for water and solution) gives the angle of rotation produced by the solution.

9.

9. The experiment is repeated with sugar solution of different strengths. (For thisThe experiment is repeated with sugar solution of different strengths. (For this 25cc. of the prepared original solution is taken in the measuring cylinder and 25cc. of the prepared original solution is taken in the measuring cylinder and water is added to it so that the volume of the solution becomes 50cc.

water is added to it so that the volume of the solution becomes 50cc.

This 50cc. obviously, contains 2.5gm of sugar. The experiment is repeated This 50cc. obviously, contains 2.5gm of sugar. The experiment is repeated with this solution. Again 25cc of the above solution is taken in the

with this solution. Again 25cc of the above solution is taken in the

measuring cylinder and water is added to it so that the volume of the solution measuring cylinder and water is added to it so that the volume of the solution becomes 50cc. This 50cc. obviously, contains 1.25gm of sugar. The

becomes 50cc. This 50cc. obviously, contains 1.25gm of sugar. The experiment is repeated with this solution).

experiment is repeated with this solution).

10.

10.The The lelengngth th of of the the popolarlarimimeteeter r tubtube e is is memeasuasured red in in dedecimcimetretres. es. SpSpececifiificc rotation is calculated for each strength of the solution separately and its mean rotation is calculated for each strength of the solution separately and its mean value is evaluated.

value is evaluated. 11.

11. Plot the grapPlot the graph betweeh between concenn concentrattration and the angle of rotatioion and the angle of rotation. It n. It will be awill be a straight line.