To start the experiment do the following:

1. Determine the cell constant of the conductivity cell by calibration with two standard potassium chloride (0.10 M and 0.01 M) solutions. The value of the cell constant is determined by measuring the conductance of the standard solutions. The conductivities for 0.10 M and 0.01 M solutions are 0.012856 mho.cm-1 and 0.0014088 mho.cm-1 respectively at 25°C. Determine the mean cell constant. Here the cell constant of the cell was 1.1 cm^-1. Note that the instrument readouts are in milli-mohs units.
2. All the solutions should be placed in a constant temperature bath maintained at 25°C for at least 20 minutes before measurements.
3. During measurement, one should take care so that no air bubbles remain trapped at the electrodes. If necessary, one has to shake the electrode gently to release the possible trapped air bubbles.
4. One has to use sufficient solution that allows full immersion of the electrodes portion of the conductivity cell in the solution.
5. After each measurement, the conductivity cell should be washed thoroughly and then be carefully dipped in a beaker containing deionized water. Before dipping the cell in the experimental solution, the water adhering to the cell should be soaked with the help of a piece of a lint free paper.
6. Prepare a 0.05 M stock solution of SDS (Mol. wt. = 288.38). SDS solution is prepared by weighing appropriate amount of SDS in an electronic or analytical balance. SDS should be weighed directly in an analytical flask. First dissolve the substance adding a small quantity of deionized water, and then it is fully dissolved by adding remaining volume of water. One must use only a very gentle mixing motion to avoid the foam formation.
7. All other solutions are prepared by exact dilution.
8. To measure the conductance at different concentrations of surfactant, prepare the most dilute solution first (see Table 1) and measure the conductance of the solution by dipping the cell in the experimental solution. Note down the reading after stabilization of the display on the instrument scale.
9. Repeat the measurement step 4 with next higher concentration. Carry out measurements always starting from the dilute sample to the next concentrated one. When proceeding to a new sample, rinse the beaker taking a small quantity of the solution whose conductance to be measured. Thus perform the measurements with all the concentrations.
10. Plot specific conductance vs. SDS concentration graph and find out the intersection of the two straight lines and their slopes.
11. Determine CMC and the degree of micellar ionization.
12. Plot molar conductance vs. square root of SDS concentration and check whether SDS behave as strong electrolyte or not (Hint: Strong electrolyte gives a linear plot). Determine the CMC value from this plot?
13. Compare the CMC values found from this experiment with the literature data.

**Table No. 1. Electrical conductivity of aqueous sodium dodecylsulfate (SDS) solutions **

TYPES OF COLLOIDS

S.No |SDS concentration[SDS] × 102 M| Measured Conductance | Specific Conductance| Molar Conductance (λ_m) | √SDS|