Table of Contents
Aim
To determine the Calcium-Magnesium hardness of given water sample.
Apparatus
Burette, pipette, conical flask.
Reagents
- EDTA (0.01 M)
- 1 N NaOH solution
- 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
- Pipette out 25m1 of water sample into a conical flask.
- Add 2m1 of 1 N NaOH, followed by 2 to 3 drops of Muroxide indicator and shake well. The solution turns pink in colour.
- Titrate this solution against Std EDTA solution taken in a burette and discontinue the titration when the colour changes from pink to purple.
- Note down the volume of EDTA run down from the burette.
Observation
| Trial No | Initial Reading | Final reading | Difference |
| 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.
