Free Carbon Dioxide Determination in Waste Water

7) FREE CARBON DIOXIDE:

Industrial waste water containing the carbon dioxide can be found by titrating the sample with Std sodium carbonate solution using phenolphthalein indicator.
Reagents
1. Phenolphthalein indicator solution
2. Std sodium carbonate
Procedure
Take 100ml of unfiltered sample in a measuring cylinder avoiding agitation. Add 10 drops of phenolphthalein indicator, run in Std sodium carbonate solution 0.5ml at a time, stirring the sample gently but thoroughly by raising and lowering a glass rod. The end point is reached when a definite pink colour persists for 5 min.
Calculation
Free carbon dioxide as (CO2), mg/l = 4.4 V
Where
V= volume in ml of Std sodium carbonate sol consumed.

Free carbon dioxide is the amount of carbon dioxide dissolved in water and waste water. The quantity of free carbon dioxide show the acidic nature of the sample water caused by carbonic acid, which is formed by reaction of carbon dioxide and water.