Determination of temporary and permanent hardness of water by complexometric titration.

Procedure

Follow these steps to determine the temporary and permanent hardness of water by complexometric titration.


    1. Standardization of EDTA sulution

    (i) In a clean and dry conical flask pipette out 20 ml of standard hard water solution.

    (ii) To this add 5 ml of ammonia buffer solution and then add 2-3 drops of EBT indicator, blue color of EBT changes to wine-red color.

    (iii) Fill the burette with EDTA solution after rinsing, note the initial burette reading. Titrate the solution in the conical flask till the wine red color changes to blue and note the final burette reading.


    2. Determination of Total hardness

    (i) Repeat the above titration method for hard water sample and note the initial and final burette readings.


    3. Determination of Permanent hardness

    (i) To remove temporary hardness take 100 ml of hard water sample in 250 ml beaker and boil it off till half of the volume is reduced and cool to room temperature.

    (ii) To remove insoluble precipitate of CaCO3 and MgCO3, filter it using Watt man filter paper.

    (iii) Make up the volume of filtered water to original 100 ml by adding distilled water.

    (iv) Now pipette out 20 ml of this solution into a clean and dry conical flask.

    (v) Repeat the titration process as mentioned under standardization of EDTA and note the initial and final burette reading of EDTA.


    Precautions:

    1. Clamp the burette perfect vertically, so that it is easy to read the scale properly.

    2. Before use rinse the burette thoroughly, while filling the burette no air bubble should be present in the burette and dispense off working solution from the burette.

    3. Remove funnel after filling burette upto mark zero. Read the lower meniscus of the burette.

    4. Add basic buffer (NH4Cl + NH4OH) to maintain the pH =10 during titration. Add ammonia buffer just before starting the titration if you add long before the titration pH of the solution may vary due to evolution of NH3(g) from the solution.

    5. Add same number of drops (vol.) of indicator in each titration.

    6. To get better visibility of color change at the end point use filter paper below the conical flask.

    7. During titration conical flask should be stirred continuously and correctly observe the end point.