Determination of Calcium-Magnesium Hardness of Water

Aim

To determine the Calcium-Magnesium hardness of given water sample.

Apparatus

Burette, pipette, conical flask.

Reagents

  1. EDTA (0.01 M)
  2. 1 N NaOH solution
  3. Muroxide

Significance

Small amounts of Ca combat corrosion of metal pipes by forming a protective coating where as appreciable Ca content, On the other hand, forms scales in boilers, pipes, utensils etc.

Principle

When EDTA is added to water containing both Ca2+ and Mg2+, it combines with Ca2+ in preference to Mg2+. When the pH is sufficiently high (12 to 13), Mg2+ is largely precipated as hydroxide and Ca2+ can be determined directly using EDTA.

Procedure

  1. Pipette out 25m1 of water sample into a conical flask.
  2. Add 2m1 of 1 N NaOH, followed by 2 to 3 drops of Muroxide indicator and shake well. The solution turns pink in colour.
  3. Titrate this solution against Std EDTA solution taken in a burette and discontinue the titration when the colour changes from pink to purple.
  4. Note down the volume of EDTA run down from the burette.

Observation

Trial NoInitial ReadingFinal readingDifference
1
2
3
4

Calculation

Calcium Hardness = [A × B × 1000] / ml of sample =                    mg/l as CaCO3 Where,

A = Volume of EDTA consumed.

B = 1 (mg of CaCO3 equivalent to 1ml of EDTA titrant)

Magnesium Hardness = Total hardness – Calcium hardness =            mg/l as CaCO3 Concentration of Ca or mg/l of Ca = {A × B × 400.8} / ml of sample.

Concentration of Mg or mg/l of Mg = 0.243 × Calcium hardness.

Total
0
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