Chemical Oxygen Demand Calculator
Compute chemical oxygen demand using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
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.
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
What formula does Chemical Oxygen Demand Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.