Course Content
Introduction to Environmental Chemistry
Environmental chemistry is the study of the chemical and biochemical phenomena that occur in nature. It involves the understanding of how the uncontaminated environment works, and which naturally occurring chemicals are present, in what concentrations and with what effects. Environmental chemistry; is the study of sources, reactions, transport, effects and fate of chemical species in water, soil and air environment as well as their effects on human health and natural environment
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Introduction
Origin of the solar System
Cosmology; is the branch of astronomy involving the study of the of the universe and the solar system. Cosmo-chemistry ;( chemical cosmology); is the study of chemical composition of the matter in the universe and the process that led to those compositions The solar system is made up of the sun (a star) with nine planets orbiting around it. These planets together with all the other heavenly bodies moving around or between individual planet form members of the solar system. Other heavenly body include; asteroids, comets, meteors, meteorites and satellites such as moon. The solar system does not include other stars .
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Origin of The Universe and Solar System
Solutions
Solutions are defined as homogeneous mixtures that are mixed so thoroughly that neither component can be observed independently of the other. The major component of the solution is called solvent, and the minor component(s) are called solute.
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Introduction
Solubility of Solutions
Solubility Product
Solution Concentrations
Chemical Equilibria
Chemical equilibrium in the environment refers to the state where the rates of forward and reverse reactions of a chemical reaction reach a balance. In this state, the concentrations of reactants and products remain constant over time, although the reactions continue to occur.
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Introduction
The Concept of Equilibrium
Relation Between Chemical Kinetics and Chemical Equilibrium
Factors Affecting Chemical Equilibrium
Laws of Chemical Equilibria
Phase Interactions
Phase interactions in solutions refer to the behavior and changes that occur when two or more substances (solutes and solvents) mix together to form a homogeneous mixture. These interactions are related to the different phases of matter, such as solids, liquids, and gases, and how they interact and transform during the process of solution formation.
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Introduction
 Phase interactions
Colligative Properties of Solutions
COLLIGATIVE PROPERTIES OF SOLUTIONS Colligative properties are physical properties of solutions that depend on the concentration of solute particles, rather than the specific identity of the solute. The four colligative properties that can be exhibited by a solution are: 1.Boiling point elevation 2.Freezing point depression 3.Relative lowering of vapour pressure 4.Osmotic pressure
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Introduction
Colligative Properties Examples
Introduction To Organic Chemistry
Organic chemistry is the study of carbon containing compounds and their properties. This includes the great majority of chemical compounds on the planet, but some substances such as carbonates and oxides of carbon are considered to be inorganic substances even though they contain carbon.
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Introduction
The IUPAC Naming (nomenclature) 
Alkyl halides, Alkenes and Alkynes
Alcohols , Ethers, Aldehydes and Ketones
Carboxylic Acids, Esters and Amines
Simple Organic Molecules in the Environment
Soil Chemistry and Pollution
soil
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Introduction to Soil Chemistry
Chemical Characteristics of Soil
Biological Characteristics of Soil
Physical Characteristics of Soil
Soil Salinity, Conductivity and Ion Exchange Capacity
Soil Pollution
Water Chemistry and Polution
Water Chemistry
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Water and the Environment
Water Chemistry
Characteristics and Properties of Water
Portable water 
Water pollution
Water Quality Analysis
Biological Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
Air Quality and Pollution
Air Quality and Pollution
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Air Quality
Testing Air Quality
Biodegradation
Biodegradation
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Biodegradation
Mechanisms of Biodegradation 
Role of Microorganisms in Biodegradation
BioGeoChemical Cycles
BiogeoChemical Cycles
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Biogeochemical cycles
The Water Cycle
The Carbon Cycle
The Nitrogen Cycle
The Phosphorus Cycle
The Sulfur Cycle
Introduction To Environmental Chemistry
About Lesson

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Chemical Oxygen Demand (COD)

Chemical Oxygen Demand (COD) is a measure of the amount of oxygen required to chemically oxidize organic and inorganic substances in water. COD testing is used to determine the overall level of organic pollution in water samples, including wastewater and surface water

Chemical Oxygen Demand (COD)  is a widely used parameter for assessing the level of organic pollutants in water bodies and wastewater.

COD is determined by measuring the oxygen consumed during a chemical oxidation process, typically using a strong oxidizing agent such as potassium dichromate (K2Cr2O7) in the presence of a strong acid. The oxidation reaction converts the organic and inorganic compounds present in the water into carbon dioxide (CO2) and water (H2O), consuming oxygen in the process. The oxygen consumed is proportional to the concentration of oxidizable substances in the water.

COD is typically expressed in milligrams of oxygen consumed per liter of water (mg/L). Unlike Biological Oxygen Demand (BOD), which relies on microbial activity for organic matter decomposition, COD measures the oxygen demand resulting from both biologically and chemically decomposable substances.

COD testing is commonly used in wastewater treatment facilities, industrial processes, and environmental monitoring to assess the effectiveness of treatment processes, evaluate the pollution load in water samples, and determine compliance with regulatory standards. High COD levels in water indicate the presence of significant organic pollution, which can deplete dissolved oxygen and negatively impact aquatic life.

The procedure for COD testing generally involves the following steps:

  1. Sample Collection: Collect a representative water sample from the water body or wastewater source to be tested for COD. Proper sample handling and storage techniques should be followed to prevent contamination and preserve the sample integrity.

  2. Digestion: Prepare a COD reagent or digestion solution, typically containing a strong oxidizing agent such as potassium dichromate (K2Cr2O7) and a catalyst. Add a specific volume of the digestion solution to a COD digestion vial or digestion flask.

  3. Sample Addition: Carefully transfer a measured volume of the water sample into the digestion vial or flask containing the digestion solution. The volume used should be appropriate for the expected COD concentration to ensure accurate results.

  4. Chemical Reaction: Heat the digestion vial or flask in a digestion apparatus, often in a water bath or heating block, to promote the chemical oxidation reaction. The heating time and temperature vary depending on the specific method being used, but typical conditions involve heating at around 150-165°C for a specified period, such as 2 hours.

  5. Cooling: After the digestion period, remove the vial or flask from the heating apparatus and allow it to cool to room temperature.

  6. Colorimetric Measurement: Use a colorimetric method or a spectrophotometer to measure the absorbance of the digested sample at a specific wavelength (often around 600 nm). The absorbance is proportional to the amount of oxidizable substances in the sample.

  7. Calibration and Calculation: Prepare a series of standard solutions with known concentrations of an organic compound, typically glucose or potassium hydrogen phthalate, and measure their absorbance using the same procedure as the sample. This calibration curve is then used to calculate the COD value of the sample based on its absorbance.

  8. Reporting: Express the COD concentration in units of mg/L or ppm (parts per million). It indicates the amount of oxygen required to chemically oxidize the organic substances in the water sample.

It is important to follow standardized methods, use proper equipment and reagents, and adhere to quality control procedures to obtain accurate and reliable COD measurements. COD testing is valuable for monitoring water quality, assessing the effectiveness of treatment processes, and ensuring compliance with regulatory standards related to organic pollution.

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