Chemical Analysis of Water

Estimation of free chlorine #

Alkalinity #

Alkalinity is present due to OH⁻, CO₃⁻², HCO₃⁻ 

• OH⁻ and HCO₃⁻ do not exist together 
• If one is present the other can’t be: OH⁻+HCO₃⁻=CO₃²⁻+H₂O

1. OH⁻  
2. CO₃²⁻ [these two consist of P, for Phenolphthalein indicator] 
3. HCO₃⁻ [the above three consist of M, for Methyl orange indicator] 

Reactions: OH⁻+H⁺ → H₂O CO₃²⁻+H⁺ → HCO₃⁻ HCO₃⁻+H⁺ → H₂O+CO₂

Determination of Alkalinity of water https://readcivil.com/determination-alkalinity-water/

1. Pipette 20 mL of sample into a clean Erlenmeyer flask (V ml).
2. Add two drops of phenolphthalein indicator. If the pH is above 8.3 the colour is pink.
3. Titrate this sample against standard acid, 0.02 N H2SO4 in the burette till the colour just disappears. Note the volume of the titrant used (V1 ml).
4. Then add two drops of methyl orange indicator. The colour turns yellow.
5. Titrate this again against the acid in the burette, till the yellow colour just turns orange-yellow.
6. Note the volume of titrant used (V2 ml)