ANALYTICAL cHEMISTRY - III

MSCM301

Experiment 5

Aim of the Experiment

To determine the total cation concentration in the water.

Principle

  • When water containing dissolved ionized salts are passed through a cation exchange resin in the hydrogen form, all the cations are removed and replaced by hydrogen ions. By this means any alkalinity present in water is destroyed and neutral product present in a solution are converted to the corresponding mineral acids. The effluent is titrated with 0.002 M NaOH solution using phenolphthalein as indicator.

  • The most abundant cations present in water are Ca2+, Mg2+, Na+, K+ and the most abundant anions present in water are bicarbonate.

  • The ionic composition of water sample is determined and chemical quality of water can be characterized and described.

  • The ionic composition of water is used to classify it into ionic types based on the dominant dissolved cation and anion expressed in milliequivalents per liter.

  • Here, we determine the total cations present in water by ion exchange method on a cation exchanger.

  • Ion exchange is a method in which ions attached to a high molecular weight polymer is normally in the form of small round sphere called beads.

  • Ion exchange resin is used to determine water and to separate mixture of ions. One important characteristic of ion exchange resin is its capacity expressed in terms of milliequivalents of exchangeable ion per g of resin.

Apparatus required

Column, Burette, Pipette, Beakers, Conical flasks, etc.

Chemicals required

2 M HCl solution, 10 ppm NaCl solution, 10 ppm KCl solution, 0.002 N NaOH solution, Cation exchange resin, etc.

Preparation of reagent

  • 0.002 N NaOH solution:

1000 mL 1N NaOH = 40 g

250 mL 0.002 N NaOH = ______ g.

  • 10 ppm NaCl Solution:

1 mg / litre = 1 µg/ mL = 1 ppm

Thus, 10 µg/ mL = 10 ppm

Procedure

1. Prepare a cation exchange column, regenerate with 2 M HCl solution and give washing with conductivity water till the column is chloride free.

2. Drain out the liquid content till above 0.5 cm from resin bead. Now, introduce 1 mL of 20 ppm Na+ and K+ mixture into the column. (mix 10 ppm 100 mL solution of Na+ and K+ and pipette out 1 mL of this solution into column)

3. Elute the mixture with 100 mL conductivity water and collect into conical flask placed at the end of the column as reservoir.

4. Titrate this 100 mL elute with 0.002 N NaOH solution from burette using phenolphthalein as indicator.

Note: set the column flow rate as 3 - 4 mL/min.

Observation

Calculations

Result

The amount of total cations present in water sample is __________ ppm.

% Error = _____________.

References

  1. G H Jeffery, J Bassett, J Mendham and R C Denney, Vogel's Textbook of Quantitative Chemical Analysis, 5th Edition

  2. Ion exchange column, https://www.youtube.com/watch?v=VUKxTJMUE4E

Developed by

Dr. Viraj Bhanvadia,

Assistant Professor, Chemistry,

viraj.bhanvadia@gsfcuniversity.ac.in