High School Quiz: Test Your Knowledge of BOD and COD

📚 Quick Study Guide

• 💧 Biochemical Oxygen Demand (BOD): The amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a water sample at certain temperature over a specific time period. Higher BOD indicates more pollution.
• 🌡️ BOD Measurement: Typically measured over 5 days at 20°C (BOD₅).
• 🧮 BOD Formula: $BOD = DO_{initial} - DO_{final}$, where $DO$ is dissolved oxygen in mg/L.
• 🧪 Chemical Oxygen Demand (COD): The amount of oxygen consumed to chemically oxidize organic matter and inorganic substances in a water sample. COD is always higher than BOD because it measures more substances.
• ⚙️ COD Measurement: Uses strong oxidizing agents like potassium dichromate ($K_2Cr_2O_7$) in acidic conditions.
• 📊 COD Formula: $COD = \frac{(A-B) * M * 8000}{mL \ of \ sample}$, where A = mL of $Fe(NH_4)_2(SO_4)_2$ used for blank, B = mL of $Fe(NH_4)_2(SO_4)_2$ used for sample, and M = Molarity of $Fe(NH_4)_2(SO_4)_2$
• ⚠️ Importance: BOD and COD are crucial indicators of water quality, helping assess pollution levels and the effectiveness of wastewater treatment.

🧪 Practice Quiz

1. Which of the following best describes Biochemical Oxygen Demand (BOD)?
   1. The amount of carbon dioxide in water.
   2. The amount of dissolved oxygen consumed by microorganisms to decompose organic matter.
   3. The amount of chemicals in a water sample.
   4. The temperature of a water sample.
2. What does a high BOD level in a water body indicate?
   1. High water quality.
   2. Low levels of pollution.
   3. High levels of organic pollution.
   4. Balanced ecosystem.
3. Which of the following best describes Chemical Oxygen Demand (COD)?
   1. The amount of oxygen required for biological processes only.
   2. The amount of oxygen required to chemically oxidize organic and inorganic matter.
   3. The amount of oxygen naturally present in water.
   4. The pressure of oxygen in a water sample.
4. Why is COD typically higher than BOD for the same water sample?
   1. COD measures only biodegradable substances.
   2. COD measures a wider range of substances, including non-biodegradable organic matter.
   3. BOD measures both organic and inorganic matter.
   4. BOD is measured at a lower temperature.
5. What is the standard temperature and duration for measuring BOD₅?
   1. 25°C for 7 days.
   2. 15°C for 3 days.
   3. 20°C for 5 days.
   4. 10°C for 2 days.
6. Which chemical is commonly used as an oxidizing agent in COD analysis?
   1. Sodium chloride (NaCl).
   2. Potassium permanganate ($KMnO_4$).
   3. Potassium dichromate ($K_2Cr_2O_7$).
   4. Hydrochloric acid (HCl).
7. What is the primary purpose of measuring BOD and COD in wastewater treatment?
   1. To determine the aesthetic appeal of the water.
   2. To assess the level of pollution and the effectiveness of treatment processes.
   3. To measure the pH of the water.
   4. To count the number of microorganisms present.