Estimation of free CO2 in water sample

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Requirement 

• Water sample
• Phenolphthalein indicator
• N/44 NaOH
• Conical flask
• Measuring cylinder
• Pipette
• Beaker

Principle 

Free CO₂ is an important chemical parameter of an aquatic ecosystem which is available in free state as carbonic acid. The value fluctuate according to acid-base buffer system. Free CO₂ influence the pH and alkalinity of water. Generally, developed due to respiration of the organism and decomposition. It is usually utilized during photosynthesis.

Procedure

Water sample was collected in a 250ml of conical flask and 100ml of the sample was taken in another conical flask in which 2-3 drops of phenolphthalein indicator was added. No any color developed.

The sample was titrated again N/44 NaOH till a permanent faint pink color just appeared. The volume of N/44 NaOH used during the titration was multiplied with 10 to obtained free CO₂ value in ppm (parts per million).

Free CO₂ in the water sample = volume of N/44 NaOH consumed × 10                  

                                                     = 0.4 ml × 10

                                                     = 4.0 ppm