TO DETERMNNE CMC (CRITICAL MICELLE CON CONT- RATION) OF GIVEN SOAP BY SURFACE TENSION METHOD USING STALAGMOMETER

 

APPARATUS REQUIRED

• Volumetric flask

•  pipette

• pyknometer

• balance

• stalagmometer

CHEMICALS REQUIRED

• Distilled water

• a stock soln of 0.05M soap.

PRINCIPLE

Soap and detergents are active materials or good examples of surface to surfactants. A surface active material absorbs solid or liquid and decreases the surface tension of the medium. The aqueous solution of soap or detergent shows the property of a colloid and when the concentration is increased, the monomeric surfactant molecules or ions colloid soap aggregate The micelle ate to form micelles or associative formation become detectable at on completes and micelles of or above certain concentration which is called critical micelle concentration. (CMC) 

eg. C17H35COONa → C17H35COO + Na+

The surface tension decrease with the increase of concentration of soap upto criticle micelle concentration and above CMC the surface tension becomes constant.

PROCEDURE

0.05M stock son was prepared (of soap) in 250ML flask. 0.0005, 0.001, 0.002, 0.004, 0.005, 0.006, 0.008, 0.01 & 0.02M Soln of the soap were prepared in 100 ml fask by diluting the stock solution.(S,V,= S₂V₂) Surface tension of each the solutions was determined using stalagmometer. The surface tension against the concentration of the soap was plotted in the graph & point of intersection of 2 lines gave the fralue of CMC of the surfactant.

OBSERVATION

Laboratory temperature -25°c 

surface tension of water (w) = 72.09

weight of empty pyknometer (W₁) = 15.96 gm

Weight of pyknometer + water (W2)= 44.46 gm

Weight of 0.0005M+Pyknometer (W)=44.51gm

Weight of 0.001M+Pyknometer (W)= 44.54gm

Weight of 0,002M+ Pyknometer (W) = 44.13gm

weight of 0.004M + pyknometer (W)= 44.41gm

weight of 0.0054 + pyknometer (W)= 44.46gm

Weight of 0.006M+ pyknometer (w)= 44.16gm

Weight of 0.008M+pyknometer (W)= 44.057gm

Weight of 0.04M+pyknometer (w) = 44.19 gm

Weight 0.02M+Pyknometer (W) = 44.43 gm

concentration of surfacetant (mol-1)	no. of drops	Weight	ds/dw=ms/mw	rs=rw.nw.ms/ns.mw rw=72.09
0.02	175	28.47	0.99	9.349
0.01	165	28.33	0.985	9.87
0.008	155	28.96	0.982	10.47
0.006	139	28.2	0.985	11.72
0.005	117	28.7	1.002	14.23
0.004	115	28.45	0.993	14.317
0.002	112	28.17	0.984	14.54
0.001	34	28.58	0.998	48.64
0.0005	26	28.55	0.997	63.54
-	23	28.64	-

RESULTS

From graph: CMC: 0.0023 mol/L Surface tension at CMC 29.5 dynes/cm Hence the CMC of given soap solution was found to be 0.0023 mol/Ltr

CONCLUSION

The critical micelle concentration (CMC) of given soap can be determined by surface tension method using stalagmometer

TO COMPARE CLEANSING ACTION OF DETERGENT 'B' AND DETERGENT 'A' WITH THE HELP OF STALAGMOMETER