Chemical Oxygen Demand Calculator
Compute chemical oxygen demand using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
COD = ((A - B) * N * 8000) / V * D
Where A is blank titrant volume (mL), B is sample titrant volume (mL), N is normality of FAS, V is sample volume (mL), D is dilution factor, and 8000 converts milliequivalents to mg O2/L.
Worked Examples
Example 1: Municipal Wastewater COD
Problem:Blank titrant = 25.0 mL, Sample titrant = 10.5 mL, FAS normality = 0.25 N, Sample volume = 20 mL
Solution:COD = ((25.0 - 10.5) * 0.25 * 8000) / 20\nCOD = (14.5 * 0.25 * 8000) / 20\nCOD = 29000 / 20 = 1450 mg/L
Result:COD = 1450 mg/L
Example 2: Industrial Effluent with Dilution
Problem:Blank = 22.0 mL, Sample = 18.0 mL, FAS = 0.1 N, Volume = 10 mL, Dilution = 5x
Solution:COD = ((22.0 - 18.0) * 0.1 * 8000) / 10 * 5\nCOD = (4.0 * 0.1 * 8000) / 10 * 5\nCOD = 320 / 10 * 5 = 1600 mg/L
Result:COD = 1600 mg/L
Frequently Asked Questions
What is Chemical Oxygen Demand (COD)?
Chemical Oxygen Demand is a measurement of the amount of oxygen required to chemically oxidize organic and inorganic matter in a water sample using a strong oxidizing agent, typically potassium dichromate. COD is expressed in milligrams of oxygen per liter (mg/L) and is a key indicator of water pollution levels. Higher COD values indicate greater contamination, with typical domestic wastewater having COD values between 250-800 mg/L, while industrial effluents can exceed 10,000 mg/L.
What is chemical equilibrium and Le Chatelier's principle?
Chemical equilibrium occurs when forward and reverse reaction rates are equal. Le Chatelier's principle states that a system at equilibrium will shift to counteract any change. Adding reactant shifts equilibrium toward products. Increasing temperature favors the endothermic direction.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy