Determination of Hardness of Water / Water Hardness

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Hardness of Water:
The presence of Calcium, Magnesium salt i.e bi-carbonates, sulphates, Chloride in water is called causes of hardness of water. The water which contains these salt is called hard water. Water's hardness is determined by the concentration of multivalent cations in the water. There are two types of hardness: Temporary hardness and Temporary hardness.

Reagent:
  1. Hardness buffer
  2. Calmagite Indicator
  3. HI 3812-0 EDTA Solution
Procedure:

For High Range – 0 to 300 mg/L CaCO3
  1. Remove the cap from the small plastic beaker. Rinse the plastic beaker with the water sample, fill to the 5 ml mark and replace the cap.

  2. Add 5 drops of Hardness Buffer through the cap port and mix carefully swirling the beaker in tight circles.
  3. Add 1 drop of Calmagite Indicator through the cap port and mix as described above. The solution becomes a red violet colour.
  4. Take the titration syringe and push the plunger completely into the syringe. Insert tip into HI 3812-0 EDTA Solution and pull the plunger out until the lower edge of the seal is on the 0 ML mark of the syringe.
  5. Place the syringe tip into the cap port of the plastic beaker and slowly add the titration solution drop wise, swirling to mix after each drop.
  6. Continue adding the titration solution until the solution becomes purple, then mix for 15 seconds after each additional drop until the solution turns blue.
  7. Read off the milliliters of titration solution from the syringe scale and multiply by 300 to obtain mg/L (ppm) CaCO3.
For Low Range – 0.0 to 30.0 mg/L CaCO3
If result is lower than 30 mg/L, the precision of the test can be improved by following the procedure below.

  1. Remove the cap from the large plastic beaker. Rinse it with the water sample, fill to the 50 ml mark and replace the cap.
  2. Proceed with the titration as for the high range test.
  3. Read off the millilitres of titration solution from the syringe scale and
  4. Multiply by 30 to obtain mg/L (ppm) CaCO3 
 
Author of This Article:
Apu Das
B.Sc. in Textile Technology
Chittagong Textile Engineering College
Facebook: Apu Das

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