Praktikum Kimia Lingkungan: Penentuan COD Sampel Air

Introduction

This tutorial provides a step-by-step guide on determining the Chemical Oxygen Demand (COD) of water samples, as showcased in the environmental chemistry practical session from the video by Analisis Kimia Sekolah Vokasi IPB. Understanding COD is crucial for assessing water quality, as it indicates the amount of organic pollutants present in the water.

Step 1: Prepare the Equipment and Materials

To accurately measure COD, gather the following materials:

• COD digestion apparatus
• COD test kits (including reagents)
• Water samples to be tested
• Glassware (flasks, pipettes)
• Distilled water for dilutions and rinsing
• Safety equipment (gloves, goggles)

Practical Tips:

• Ensure all glassware is clean to avoid contamination.
• Wear safety gear to protect against chemical exposure.

Step 2: Sample Collection and Preparation

Follow these steps to collect and prepare your water samples:

1. Collect water samples in clean, dry containers.
2. If possible, analyze samples immediately; if not, store them in a cool, dark place.
3. Measure a specific volume of the water sample (usually 50 mL) using a graduated cylinder or pipette.

Common Pitfalls:

• Avoid exposing samples to sunlight, as this can alter their composition.
• Ensure that the sample volume is consistent for accurate results.

Step 3: Add Reagents

To each water sample, add the required reagents from the COD test kit:

1. Add the appropriate amount of potassium dichromate (usually about 10 mL).
2. Add sulfuric acid carefully to the sample.
3. Mix the solution gently to ensure even distribution of the reagents.

Practical Advice:

• Always add acid to water, not the other way around, to prevent exothermic reactions.
• Follow the instructions provided with your COD test kit for precise reagent amounts.

Step 4: Digest the Samples

Place the prepared samples in a COD digestion block:

1. Set the temperature on the digestion block to 150°C.
2. Insert the samples and allow them to digest for a specified time (typically 2 hours).

Safety Reminder:

• Ensure the digestion block is in a well-ventilated area and follow all safety protocols when handling hot equipment.

Step 5: Measure the COD

After digestion, allow the samples to cool. Proceed to measure the COD:

1. Use a spectrophotometer to analyze the samples.
2. Prepare a calibration curve using standard COD solutions.
3. Measure the absorbance of your samples and compare it to the calibration curve to determine COD values.

Real-World Application:

• Understanding the COD levels helps in evaluating the potential impact of pollutants on aquatic life.

Conclusion

In this tutorial, we covered the essential steps for determining the Chemical Oxygen Demand of water samples. By preparing your equipment, collecting samples correctly, adding the right reagents, digesting the samples, and measuring the results accurately, you can effectively assess water quality. Next steps may include exploring the implications of your findings on environmental health or further testing for specific pollutants.