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Free Carbon Dioxide and Chemical Oxygen

Problem-free analyzed carbon dioxide that is in the form of carbon dioxide gas contained in water. The content of CO 2-free in pure water at a pressure of 1 atm and a temperature of 25 ° C is about 0.4 ppm. CO 2 in water is obtained from the air of the diffusion process and the results of the process of respiration of aquatic organisms. the bottom waters of the CO 2 is also generated by the decomposition process. commonly used method for the measurement of CO 2 is free titrimetric method with sodium carbonate (Na 2 CO 3).

Principle analysis of free carbon dioxide reacts with sodium carbonate or sodium hydroxide to form sodium bicarbonate standard three colorless solution that requires penolpthalein indicator (PP) which will give a red / pink when the solution becomes alkaline (pH> 8.3). so that the slightest excess sodiumkarbonat or sodium hydroxide solution will cause red marks the end of titration. Measurements of carbon dioxide-free titration method can be carried out according to the procedures below

Tool :
 reaction tubes
 Pumpkin erlenmeyer
 Buret and the stand

Material :
 Indicators Phenol ptalein
 Sodium bicarbonate

Ways of working :
 Enter the 50 mL water sample into erlenmeyer flask.
 Add 3-5 mL PP indicators.
 Titration standard bicarbonate Ntrium dropwise until pink.
 Note mL Sodium bicarbonate is standard in use.

Calculation :
Levels of CO 2 = 1000 x mL Na-Na-bicarbonate bicarbonate x x BA Na-bicarbonate

COD (Chemical Oxygen Demand)
COD (Chemical Oxygen Demand) stating the total amount ooksigen needed to oxidize all of the organic material contained in the waters, into CO2 and H2O. COD value will increase with increasing value of organic matter in the water. COD inversely with Dissolved Oxygen (DO). That is, the less the air content in the water, the COD number will be even greater.

The amount of COD figures show that the presence of organic substances in the water are in large numbers. The organics are changing oxygen into carbon dioxide and water so that the water becomes starved of oxygen. This is the indicator of how much contamination in the wastewater by the disposal of domestic and industrial. The less oxygen in the water means that the greater the amount of pollutants (organic) in these waters.

Therefore logically we can say that the water we consume must have very low levels of COD. In principle the measurement of COD is the addition of a certain amount of potassium bichromate (K 2 Cr2O 7) as an oxidant in the sample (with a known volume) which has been added the concentrated acid and silver sulfate catalyst, then heated for some time. Furthermore, excess potassium bichromate ditera by titration.

Thus potassium bichromate are used for the oxidation of organic material in the sample can be calculated and the value of COD can be determined. The disadvantage, inorganic complex compounds in water that can be oxidized also participate in the reaction, so that in certain cases the COD value may be slightly ‘over estimate’ for a description of the content of organic material. COD can be measured in two ways, namely by:
a) COD meter
Kubet each containing samples and blanks are added Potassium Dichromate (K2Cr2O7) 0,25N 2 ml Shaken then introduced into the reactor for 2 hours COD readings Forum on DR 2000, after 2 hours reading Record
b) Titration (reflux)
Tool :
(1) The Erlenmeyer flask, cooling Liebing 30 cm
(2) Hot Plate
(3) flask of 100 ml and 1000 ml
(4) Buret 50 ml
(5) Pipette volume of 5 ml, 10 ml, 15 ml and 50 ml
(6) 250 ml Erlenmeyer flask (flask reflux)
(7) Scales analytical
(8) Pots
(9) basin to cool

Material :
(1) The sample solution 10ml
(2) Material Solution Potassium dichromate (K2Cr2O7) 0,25N
(3) K2Cr2O7 solution was diluted with distilled water
(4) Sulfuric Acid solution – silver sulfate
(5) indicator solution Ferroin
(6) solution of ferrous ammonium sulfate (FAS) 0,1N
(7) standard solution of potassium hydrogen phthalat (KHP)
(8) Powder mercury sulfate (HgSO4)
(9) Stone Boiling
(10) Distilled

Procedure :
(1) 125 ml Erlenmeyer washed clean, free of organic material
(2) 10 ml of water sample is introduced into erlenmeyer using a pipette,
(3) Added 5 ml K2Cr2O7 and stir
(4) was then added cautiously 15 ml of concentrated H2SO4 (using the hood),
(5) Erlenmeyer covered with a glass cover and left for 30 minutes,
(6) After it was diluted by adding 7.5 ml of deionized distilled water and stir
(7) Added 2-3 drops of indicator Ferroin, then titrated with fas until the color changes from yellow, orange or turquoise to red-brown,
(8) After it made the reference solution with 10 ml of distilled water in the same way,

Calculation :
COD (mg / l) = ((AB) × N × 8000) ml sample
Description: A: FAS volume needed for the blank (ml) B: FAS solution volumes required for the sample (ml)
N: Normality FAS solution Limits COD (100-300) mg / L


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