Titrasi Argentometri metode Mohr (Tutorial Prosedur analisis kadar NaCl + perhitungan)

Introduction

This tutorial guides you through the argentometric titration method, specifically using the Mohr method to analyze sodium chloride (NaCl) concentration. This procedure is essential in analytical chemistry for measuring halides and other compounds that form precipitates with silver nitrate (AgNO3). By following these steps, you will learn how to perform the titration, identify the endpoint using potassium chromate as an indicator, and understand the calculations involved.

Step 1: Prepare Your Materials

Gather all necessary materials before starting the titration process:

• Reagents:

  • Silver nitrate (AgNO3) solution
  • Sodium chloride (NaCl) solution (the analyte)
  • Potassium chromate (K2CrO4) solution (the indicator)

• Equipment:

  • Burette
  • Conical flask
  • Pipette
  • White tile (to better observe color changes)
  • Stirring rod
  • Analytical balance (for precise measurements)

Practical Tip: Ensure all glassware is clean and rinsed with the solutions to avoid contamination.

Step 2: Set Up the Titration

Follow these steps to prepare for the titration:

1. Fill the Burette:

   • Rinse the burette with the AgNO3 solution, then fill it without air bubbles. Record the initial volume.

2. Prepare the Analyte:

   • Using a pipette, measure a specific volume of the NaCl solution (e.g., 25 mL) and transfer it to the conical flask.

3. Add the Indicator:

   • Add 1-2 drops of potassium chromate solution to the NaCl solution in the conical flask.

Step 3: Conduct the Titration

Now, perform the titration by following these steps:

1. Titrate the Sample:

   • Gradually add the AgNO3 from the burette to the NaCl solution while continuously swirling the flask.

2. Observe the Endpoint:

   • Continue adding AgNO3 until you observe a persistent color change to reddish-brown. This indicates the formation of silver chromate (Ag2CrO4), signaling the endpoint of the titration.

Common Pitfall: Avoid adding too much AgNO3, as this can lead to inaccurate results.

Step 4: Record and Calculate Results

After reaching the endpoint, it's time to calculate the concentration of NaCl:

1. Note the Final Burette Reading:

   • Subtract the initial volume from the final volume to determine the volume of AgNO3 used.

2. Perform Calculations:

   • Use the following formula to calculate the concentration of NaCl:

   [ C_{NaCl} = \frac{C_{AgNO3} \times V_{AgNO3}}{V_{NaCl}} ]

   Where:

   • (C_{NaCl}) = concentration of NaCl
   • (C_{AgNO3}) = concentration of silver nitrate
   • (V_{AgNO3}) = volume of AgNO3 used
   • (V_{NaCl}) = volume of NaCl solution

Practical Tip: Ensure units are consistent when performing calculations.

Conclusion

In this tutorial, you learned the argentometric titration method using the Mohr technique to analyze sodium chloride. You prepared the necessary materials, set up the titration, conducted the procedure, and calculated the concentration of NaCl. This method is widely applicable in various fields, including food science, environmental testing, and pharmaceuticals. For further practice, consider applying this technique to other halides or compounds that form precipitates with silver nitrate.