p - 19 Determination of Dissolved CO2

Part  – I

Last Update: January 24, 2007

M  – 19

DETERMINATION OF FREE CARBON -DI-OXIDE WATER  Free CO2 in neutral water is determined by titration with Na 2CO3 or NaOH to form NaHCO3 completion of the reaction indicates the development of pink colour of phenolphthalein indicator of the equivalent. The sample should be gently swirled during the titration but care must be taken before and during titration to keep aeration at a minimum. NaOH + CO2 + H2O = NaHCO3 i) Measuring cylinder ii) Conical flask iii) Burette iv) Burette stand. i) N/44 N/44 NaOH ii) Phenolphthalein indicator iii) Sample water 50 ml of sample water is taken in a conical flask and 2-3 drops of phenolphthalein is added. If the water turns to pink then there is no free CO 2 in water sample. If the sample remain colourless it is titrated with standard alkaline solution (NaOH or Na2CO3). Gentle string during titration is done until pink colour persists for 30 sec. The colour change indicates the end point of titration.

No of Observtion 1. 2. 3.

 As,

Vol of sample water (ml) 50 50 50

Buratte Reading (ml) Initial Final 0 0.6 1 1.6 2 2.6

Differences (ml) 0.6 0.6 0.6

Mean (ml) 0.6

1 mole of CO2  1 mole of NaOH 44 gm of CO2  40 gm of NaOH 1000 cc (N) NaOH  44 gm of solid NaOH 1000 cc (N) NaOH  44 gm of CO2 1000 cc (

 N  44

)NaOH = 44 / 44 44 gm of CO2 = 1 gm of CO2 = 1000 mg of CO2

N

1 ml (  / 44 44) NaOH  1 mg of CO2 0.6 ml (  / 44 44) NaOH  0.6 mg of CO2 Therefore 50 ml of sample sample water contains 0.6 mg of CO2 

N

1000 ml of sample water contains

0.6  100 50

 mg of CO2 = 12 mg of CO2

So the supplied sample contains 12 mg of CO 2 / lit or 12 ppm.  As CO 2 is liable to escape easily from the sample, analysis should be done immediately after collection of it. Stirring should be done gently during titration.

CO2  plays the same role in both aquatic & terrestrial system in fact it is utilized by the plants during photosynthesis. Besides this is an aquatic system amount of free CO 2 influences the metabolic and developmental rates, orientation and movement of some aquatic invertebrates after binding allow them to the oven for overnight.  According to swingle (1947) effect of dissolved O 2 level on fish population are stated below. Dissolved O2 ( ppm ) <1 1–5 >5 5 – 15

Effects. Lethal on exposure for more than few hours. Fish will survive, but reproduction and growth be poor. Normal growth and reproduction. Good for drinking purpose.

Therefore, from this result we can conclude that this water is not suitable for fish culture. Fish will survive, but the rate growth and reproduction will be poor.