SETUP DESCRIPTION :

The setup consists of a cylinder of benzoic acid mounted on a SS rod and with a D.C. motor. The operational range of rotation is between 10 to 30 rpm. The cylinder is immersed in an aqueous solution of sodium hydroxide of known concentration in a 500 ml vessel filled to two-third its capacity. The position of the benzoic cylinder is so adjusted that the liquid level rises above the top surface by about the top surface by about 3 cm. The dimensions of the benzoic acid may be fixed at diameter 2 or 3 cm,length 5 to 7 cm. the cylinder can be prepared by pouring molten benzoic acid in the mould of desired dimensions with 4 to 5 mm SS rod located in the center of the mould in a vertical position .

 

 

PROCEDURE :

1. Record the dimensions of the benzoic acid cylinder(o.d.,length and od of ss rod) and then fix it in a vertical position with the d.c motor.

2. Fill the vessel with aqueous naoh solution of known concentration upto 2/3rd of its volume.record the volume of aqueous NaOH solution added (v).

3. Start the water bath and fix the dissolution temperature,ambient upto 50 degree Celsius .

4. Fix the benzoic acid cylinder inside the vessel containing aqueous NaOH solution and start the motor at a fixed rortional speed N rpm.

5. Run the experiment for 10 minutes.

6. Stop the motor and remove benzoic acid cylinder and measure its dimensions again.

7. Mix thoroughly the contents of the vessel and analyse it for unreacted NaOH concentration by titration against standard HCl solution.

8. Measure the benzoic acid cylinder dimensions again.

9. Repeat steps 1 to 8 for different concentrations of aqueous NaOH solutions.

10. Repeat steps 1 to 8 using de-ionised water. This run may be carried for about 45 to 60 minutes duration. During this period small samples should be withdrawn at regular intervals of 10 minutes and analyzed for dissolved benzoic acid by titration against 0.02kmol/m3 NaOH solution.