Determination Of Ion Exchange Capacity For Cation

Technically, resin capacity is a measurement of total capacity, as determined by a test performed in the lab by a titration methodology. A measured quantity of cation resin, for example, is fully converted to the hydrogen (H) form with an excess of strong acid and then well rinsed. A measured quantity of Sodium Sulphate is then passed through the resin so as to totally exhaust the resin. The effluent is captured. The Sodium sulphate that passed through the column represents the sodium (Na) ions that were not captured by the resin. This solution is then titrated with Sodium hydroxide to neutralize it and the amount of NaOH required is expressed in equivalents. The difference between the total equivalents of Sodium sulphate passed through the column and the Sodium sulphate exiting the column represents the total equivalents of Na captured by the resin. The capacity of the resin is then determined.

Exchange capacity can be measured by exchanging sodium ion (Na+) for hydrogen form (H+ initially attached to the resin).  The hydrogen ion is then titrated with standard sodium hydroxide solution.  The exchange reaction can be represented as:

2R-H⁺ + 2Na⁺_(aq) + SO₄^-2_(aq) ⇔ 2R-Na⁺ + 2H⁺_(aq) + SO₄^-2_(aq)

PURPOSE: 

This procedure is to determine the Total ion exchange capacity of Cation exchange resin.

 REQUIREMENTS:              

0.25 M Sodium sulphate

0.1 N Sodium hydroxide

Phenolphthalein indicator

PROCEDURE:

The column is assembled from three pieces; a relatively long glass column, a valve assembly, and a delivery tip.  Before using the column, test it for leaks by filling it with water.  If it leaks, tell your instructor so that the problem can be corrected before you start the experiment.  Place a small plug of glass wool at the bottom of the chromatography column.  The glass wool prevents beads of ion exchange resin from plugging the valve assembly

1.      1.  Weigh accurately about 0.5 g resin (Previously moisture removed by tissue paper) and transfer               into a 15 cm column.

       2. Prepare 250 ml 0.25 M Sodium sulphate solution and transfer into 500 ml separating funnel.

       3. Allow the solution to drip into the column at a rate of about 2 ml per minute.

4.      4. Collect the effluent into a 500 ml conical flask.  When all the solution has passed through the                  column.

       5. Titrate the effluent with 01 N Sodium hydroxide using phenolphthalein as an indicator.

 CALCULATION:

                                                       V     X      A         
                                Assay      =     ---------------  
                                                              W
                                     V         =     Titer value
                                    N         =     Normality of 0.1N Sodium hydroxide solution.
                                    W        =    Weight of Resin