Praktikum Kimia Analisis - 8. Gravimetri (Bagian Kedua)

Summary

This script details a step-by-step guide for an online quantitative analysis chemistry practical, focusing on the filtration and gravimetric determination processes. It covers the preparation of filtering apparatus, the process of filtering and separating the filtrate, and checking for impurities. After confirming the absence of contaminants, the procedure moves to heating, drying, and weighing the porcelain crucibles to achieve constant weight. It also includes repeated heating and weighing for accuracy, and concludes with calculations to determine the mass of the sample. The overall aim is to teach students essential laboratory techniques in gravimetric analysis.

Takeaways

• 😀 The experiment is conducted online due to certain limitations preventing a physical lab session.
• 😀 The filtering process requires specific equipment: a glass funnel, an Erlenmeyer flask, filter paper, and tweezers.
• 😀 Proper folding of filter paper is essential for successful filtration. The paper should be folded in half, then in quarters, and placed in the funnel correctly.
• 😀 Filtration separates the filtrate from the residue, ensuring no solid particles remain in the liquid.
• 😀 It is important to check the filtrate for any cloudiness, indicating the presence of impurities, and repeat the precipitation process if necessary.
• 😀 The chloride ion (Cl-) presence in the filtrate is tested using a silver nitrate (AgNO3) solution. No white precipitate indicates the absence of chloride.
• 😀 After filtration, the beaker and stirring rod should be rinsed with warm water to remove any remaining sample.
• 😀 The filter paper is then heated in a crucible to ensure complete drying of the sample, using a Bunsen burner and a tripod.
• 😀 After heating, the crucible is placed in a desiccator to cool before weighing to avoid moisture interference.
• 😀 The weighing process ensures constant mass is achieved for accuracy, with measurements repeated three times to confirm consistency.

Q & A

What is the purpose of the filtration process in this gravimetric analysis?

The filtration process is used to separate the solid residue from the liquid (filtrate), ensuring that only the clear solution is further analyzed, while the precipitate is removed for further processing.

How should the filter paper be prepared before use?

The filter paper should be folded into two parts and then folded again to form a cone. This ensures the paper fits neatly into the funnel and allows effective filtration.

Why is the filtrate checked for cloudiness during the filtration process?

The filtrate is checked for cloudiness to ensure that all solid particles have been removed. If any cloudiness is observed, it indicates that further sedimentation or filtration is needed.

What is the purpose of testing the filtrate with AgNO3?

The AgNO3 test is used to check for the presence of chloride ions (Cl⁻) in the filtrate. If a white precipitate forms, it indicates that chloride ions are still present in the solution.

How is the presence of chloride ions detected in the filtrate?

The presence of chloride ions is detected by adding silver nitrate (AgNO3) to the filtrate. If a white precipitate forms, it confirms the presence of chloride ions.

What steps are involved in the process of heating the filter paper with the residue?

The filter paper containing the residue is placed into a porcelain crucible, and the crucible is heated over a Bunsen burner. This process, called calcination, burns off any organic material and leaves behind an inorganic residue.

Why is it important to place the crucible in a desiccator after heating?

After heating, the crucible is placed in a desiccator to cool in a moisture-free environment. This prevents the residue from absorbing moisture from the air, which could affect the final weight measurement.

How is the final weight of the sample determined in gravimetric analysis?

The final weight of the sample is determined by weighing the crucible with the residue after it has cooled. The weight is measured multiple times until the results are consistent, with a difference of no more than 0.2 mg between successive weighings.

What is the purpose of performing the calcination step multiple times?

The calcination step is repeated to ensure that all organic material is completely burned off, leaving only the inorganic residue. This ensures accurate and consistent results during the weighing process.

What is the significance of ensuring that the balance’s water pass is centered during weighing?

Ensuring that the balance's water pass is centered ensures that the weight measurement is accurate and unaffected by external factors such as uneven placement or air currents.