CTC 114: Introduction to the Separatory Funnel and Immiscible Liquids Pre-Lab Discussion

Summary

The video covers a laboratory experiment focused on using a separatory funnel for liquid-liquid extraction. The separatory funnel helps separate immiscible liquids into two distinct layers. In Part A, students will compare two solvents, dichloromethane (DCM) and hexanes, to extract iodine from a solution. Part B involves extracting benzoic acid and comparing single vs. multiple extraction methods. Part C repeats the process with salicylic acid, using a UV-Vis spectrometer to measure absorbance. The experiment aims to test students' technique in using the separatory funnel and their ability to analyze results using laboratory equipment.

Takeaways

• 🔬 The separatory funnel is a key piece of glassware used in laboratories to separate immiscible solutions, which form two distinct layers.
• 💡 Immiscible means that the solutions do not mix, and the separatory funnel helps to easily separate them by tapering toward the bottom.
• 🧪 In Part A of the experiment, students will use two solvents—dichloromethane (DCM) and hexanes—to determine which one better extracts iodine from a solution.
• ⚠️ Both dichloromethane (DCM) and hexanes are potential carcinogens, so handling them with care is important.
• 🎨 The color of the iodine solution will help indicate which solvent extracts more iodine, with the darker color showing better extraction.
• 🧼 Part B of the experiment uses benzoic acid, which is colorless, requiring a titration method to measure extraction instead of visual observation.
• 🌡️ In Part B, the experiment compares single-step extraction versus multiple-step extraction to determine which method is more effective.
• 📏 The titration process in Part B will involve using a burette to determine the amount of solvent extracted by recording the endpoint as the solution turns pink.
• 💊 Part C uses salicylic acid, and instead of visual observation, the UV-Vis spectrometer will measure the color intensity after adding a ferric solution.
• 📊 A calibration curve will be provided to help calculate the concentration of the extracted substance using the absorbance value measured in the UV-Vis spectrometer.

Q & A

What is the purpose of a separatory funnel?

The purpose of a separatory funnel is to separate two immiscible liquids, allowing for the easy separation of layers based on their densities.

What are the two solvents used in Part A of the experiment?

The two solvents used in Part A are dichloromethane (also known as DCM or methylene chloride) and hexanes.

Why are DCM and hexanes considered hazardous in the lab?

Both DCM and hexanes are classified as carcinogens, meaning they have the potential to cause cancer, although there isn't concrete evidence. Precautions should be taken to avoid inhaling vapors or direct contact with these chemicals.

How can you tell which solvent is the better extraction solvent in Part A?

The solvent that produces a darker solution (more iodine dissolved) is considered the better extraction solvent because it has pulled more iodine into the solution.

What compound is used in Part B of the experiment and why is it challenging to visually observe the extraction?

Part B uses benzoic acid, which is colorless. The challenge is that there is no color change to visually track the separation, so a different method is required to measure the amount extracted.

How is the effectiveness of a single extraction compared to multiple extractions in Part B?

In Part B, the experiment compares a single extraction using 20 mL of solvent versus multiple extractions with smaller amounts (4 extractions with 5 mL each). The goal is to determine which method extracts more benzoic acid.

What technique is used to measure the amount of benzoic acid extracted in Part B?

A titration technique is used to measure the amount of benzoic acid extracted. The endpoint of the titration is when the solution turns pink, and the volume of titrant used is recorded.

What is the compound used in Part C of the experiment, and what is it commonly found in?

The compound used in Part C is salicylic acid, which is commonly found in face creams, lotions, and acne treatment products.

How do you determine the concentration of salicylic acid extracted in Part C?

The concentration of salicylic acid is determined by adding ferric chloride or ferric nitrate to the solution, which produces a color change. The solution's absorbance is measured using a UV-Vis spectrometer, and the concentration is calculated using a provided calibration curve.

Why is a UV-Vis spectrometer used in Part C instead of visual observation?

A UV-Vis spectrometer is used because the solutions are colorless and cannot be visually distinguished. The instrument measures how much light the solution absorbs, providing a quantitative way to determine concentration.