Penentuan Fosfor Dalam Tanah Dengan Spektrofotometer UV-Vis

Summary

This video script provides a detailed guide to conducting a soil phosphorus determination experiment using a UV-Vis spectrophotometer. It covers the necessary materials and tools, starting with the water content measurement of soil. The script walks through the preparation of test samples, including the addition of HCl and a standard P2O5 solution, followed by a one-hour stirring process. The procedure also includes preparing a standard solution series and conducting absorbance readings for both the sample and standard solutions. The final steps involve using the spectrophotometer to measure maximum wavelength and absorbance, with results entered into Excel for analysis.

Takeaways

• 😀 Distilled water, citric acid (2%), and 25% HCl are some of the essential materials needed for the phosphorus determination process.
• 😀 The experiment begins with determining the water content in the soil by weighing the soil sample before and after drying.
• 😀 Soil samples are placed in a porcelain cup, oven-dried at 105°C for three hours, and then cooled in a desiccator before weighing again.
• 😀 A sample of 2 grams of soil is added to 10 mL of 25% HCl to prepare the sample for further analysis.
• 😀 The sample is stirred for one hour, then split into two: one for the sample and one for the spike.
• 😀 The sample and spike are pipetted with 2% citric acid to ensure proper dilution before adding the reagents.
• 😀 Ammonium molybdate vanadate solution is added to the sample and spike for phosphorus determination.
• 😀 After preparing the sample, it's diluted with distilled water to a 100 mL mark, ensuring proper homogenization.
• 😀 Standard solutions of P2O5 with a concentration of 1000 PPM are used to create a series of standards with different concentrations.
• 😀 A UV-Vis spectrophotometer is used to measure the absorbance of the sample and the standard solutions, beginning with finding the maximum wavelength.
• 😀 The absorbance data is entered into Excel for further analysis and interpretation of phosphorus levels in the soil samples.

Q & A

What is the primary objective of this practicum?

The primary objective of the practicum is to determine the phosphorus content in soil samples using a UV-Vis spectrophotometer.

What are the key materials required for the experiment?

Key materials required for the experiment include distilled water, citric acid (2%), 25% HCl, a standard solution of P₂O₅ (1000 PPM), ammonium molybdate vanadate solution, filter paper, soil samples, and various glassware.

How do you determine the water content in the soil sample?

The water content in the soil sample is determined by weighing the empty porcelain cup, adding 1 gram of the soil sample, drying it in an oven at 105°C for 3 hours, and then weighing it again after cooling in a desiccator.

Why is the sample stirred with a stirrer for 1 hour during preparation?

The sample is stirred with a stirrer for 1 hour to ensure that the soil sample and reagents are thoroughly mixed and to facilitate the extraction of phosphorus for analysis.

What is the purpose of adding ammonium molybdate vanadate solution to the sample?

Ammonium molybdate vanadate solution is added to the sample to react with the phosphorus, forming a complex that can be measured using the UV-Vis spectrophotometer.

What is the significance of preparing a standard series for the UV-Vis spectrophotometer?

Preparing a standard series is important to create a calibration curve that allows for the accurate determination of the phosphorus concentration in the unknown soil samples based on their absorbance readings.

How is the maximum wavelength for the UV-Vis spectrophotometer determined?

The maximum wavelength for the UV-Vis spectrophotometer is determined by measuring the absorbance of the standard series solutions and identifying the wavelength that gives the highest absorbance.

Why is the UV-Vis spectrophotometer instrument covered and cleaned before use?

The UV-Vis spectrophotometer is covered and cleaned before use to ensure there is no contamination or interference from dirt or residues that could affect the accuracy of the measurements.

How is the phosphorus concentration in the soil sample determined after measurement?

The phosphorus concentration in the soil sample is determined by comparing its absorbance value to the calibration curve derived from the standard series.

What are the advantages and limitations of the UV-Vis spectrophotometry method for determining phosphorus in soil?

The advantages include high accuracy and precision in determining phosphorus concentrations. However, limitations include potential errors in sample preparation or calibration, which could affect the results.