Melaksanakan Analisis Kolorimetri Mengikuti Prosedur - Teknik Kimia

Summary

The video is a practical chemistry lesson on the colorimetric method, specifically using photometry to determine potassium permanganate concentration. The instructor guides students through preparing standard and sample solutions, setting up the spectrophotometer, measuring absorbance at optimal wavelengths, and calculating sample concentration using the standard absorbance. The session combines clear step-by-step instructions with hands-on demonstration, emphasizing accuracy in solution preparation and measurement. Students actively participate in the experiment, learning to apply theoretical knowledge to practical lab work. The lesson concludes with recording results and reinforcing proper laboratory techniques, offering a comprehensive, engaging introduction to colorimetric analysis.

Takeaways

• 😀 The lesson begins with a greeting and a quick check-in with students about their well-being.
• 😀 The main topic of the lesson is the colorimetric method, a chemical analysis technique based on color comparison.
• 😀 There are two types of colorimetric methods: visual colorimetry (using the eye) and photometric colorimetry (using a photosensor).
• 😀 The practical experiment focuses on determining the concentration of potassium permanganate using photometric colorimetry.
• 😀 Students are instructed to prepare the potassium permanganate sample and calculate the volume needed for dilution to create a standard solution.
• 😀 Proper handling includes transferring 2.5 mL of stock potassium permanganate solution into a 50 mL volumetric flask and adding distilled water to the mark.
• 😀 Homogenization and careful drying of the flask neck with tissue are emphasized before measurement.
• 😀 The spectrophotometer is set to 420 nm initially, with a blank measured at 100% transmittance, followed by recording absorbance for standard and sample solutions.
• 😀 The wavelength with the highest absorbance is identified (510 nm), and measurements are repeated to obtain accurate absorbance data.
• 😀 The sample concentration is calculated using the formula: sample concentration = (sample absorbance / standard absorbance) × standard concentration.
• 😀 The experiment concludes with recording the results, with a correct example given as 71.74 ppm for the potassium permanganate sample.

Q & A

What is the colorimetric method in chemical analysis?

The colorimetric method is a chemical analysis technique based on comparing the color intensity of a sample solution with a standard solution. It can be done visually or using instruments like a photometer.

What are the two types of colorimetric methods mentioned in the transcript?

The two types are visual colorimetry, which uses the human eye as a detector, and photometric colorimetry, which uses a photosensor or photodetector to measure absorbance.

What substance is being analyzed in the practical experiment?

The substance being analyzed is potassium permanganate (KMnO4).

What is the purpose of preparing a standard solution in this experiment?

The standard solution of potassium permanganate is prepared to have a known concentration. It serves as a reference to determine the concentration of the unknown sample by comparing absorbance values.

How is the absorbance of a solution measured in this experiment?

Absorbance is measured by first setting the photometer to a specific wavelength, inserting a blank cuvette to calibrate the device to 100%, and then inserting the sample or standard solution to record its absorbance value.

Why is the wavelength set to 420 nm initially and later changed to 510 nm?

The initial measurement at 420 nm allows preliminary readings, while 510 nm corresponds to the wavelength at which potassium permanganate shows maximum absorbance, providing the most accurate data for concentration determination.

What formula is used to calculate the concentration of the sample?

The concentration of the sample is calculated using: Sample concentration = (Absorbance of sample ÷ Absorbance of standard) × Concentration of standard.

Why is it important to homogenize the solution in the volumetric flask?

Homogenizing ensures that the solution is uniformly mixed, so the concentration throughout the solution is consistent and measurements are accurate.

What is the role of the blank solution in this experiment?

The blank solution, usually distilled water, is used to calibrate the photometer to 100%, eliminating background interference so that only the sample's absorbance is measured.

What steps should be taken to prepare a diluted standard solution from a stock solution?

Measure a precise volume of the stock solution, transfer it into a volumetric flask, add distilled water up to the calibration mark, and mix thoroughly to obtain a homogenous standard solution.

What value of potassium permanganate concentration was obtained in the sample according to the transcript?

The concentration obtained for the potassium permanganate sample was 7.174 ppm (parts per million).

Why is it necessary to wipe the neck of the volumetric flask with tissue during preparation?

Wiping the neck removes any droplets that may stick to the glass, ensuring accurate volume measurement and precise concentration in the solution.