Chemistry Post-Lab: Solvent & Pigment Extraction

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Questions and Answers

What is the primary purpose of solvent extraction in the experiments conducted?

To dissolve the samples for observation.

To extract pigments from the samples.

To analyze the physical properties of the solvents used.

To measure the % yield and determine partition coefficient (Kp). (correct)

Which of the following is NOT a method of solvent extraction discussed in the experiments?

Liquid-liquid extraction

Solid-liquid extraction

Gas-liquid extraction (correct)

Liquid-solid extraction

Which solvent was specifically mentioned for dissolving samples in Experiment 1?

Diethyl Ether

EtAc (correct)

Acetone

Ethanol

In the context of solid-liquid extraction, which of the following is a correct example?

Extracting pigments from fruits using ethanol. Signup and view all the answers

What observation was likely expected after dissolving samples in both H2O and EtOH?

Different solubility patterns suggesting varying polarities. Signup and view all the answers

What are emulsions primarily composed of?

Tiny droplets suspended between polar and non-polar layers Signup and view all the answers

What condition is necessary for the extraction and solution solvent in solvent extraction?

The solvents must be immiscible with each other Signup and view all the answers

What is the role of detergents in an emulsion?

To stabilize the emulsion and prevent separation Signup and view all the answers

What issue does 'salting out' address in solvent extraction?

Separation of layers obscured by dark colors Signup and view all the answers

Which of the following is NOT a requirement for an extraction solvent?

Must be highly flammable and toxic Signup and view all the answers

How can one visualize the interface when it cannot be seen due to dark layers?

Using a flashlight to shine through the solution Signup and view all the answers

Which of the following solvents has a higher density based on the given data?

Ethyl acetate (0.90 g/mL) Signup and view all the answers

What does the Beer-Lambert Law express?

The relationship between absorbance and concentration. Signup and view all the answers

Why is a quartz cuvette preferred over other materials for measuring absorbance?

It allows light to pass with minimal interference. Signup and view all the answers

What role does dark incubation play in pigment extraction?

It minimizes light-induced degradation of pigments. Signup and view all the answers

What is the order of solubility of salicylic acid from highest to lowest in various solvents?

Ethanol, Ethyl Acetate, Carbon Tetrachloride, Xylene, Water Signup and view all the answers

What unit is used to express molar absorptivity in the content?

L mol⁻¹ cm⁻¹ Signup and view all the answers

If a compound has an absorbance of 1.35 in a 10-mm cuvette, what might be inferred about its concentration?

It has a high concentration. Signup and view all the answers

Among the solvents listed, which has the highest boiling point?

Water Signup and view all the answers

Which solvent has a reported miscibility with water?

Ethanol Signup and view all the answers

What is the purpose of using acetone, methanol, and ethanol in pigment extraction?

To enhance the solubility of different pigments. Signup and view all the answers

What effect does cohesive energy have on the solubility of salicylic acid?

Lower cohesive energy is linked to higher solubility in ethanol and ethyl acetate. Signup and view all the answers

What information is conveyed by the unique wavelength (wv) of a compound's absorbance?

It is specific to the type of compound present. Signup and view all the answers

How is pigment concentration determined after absorbance measurement?

Using the Beer-Lambert Law formula. Signup and view all the answers

At what temperature is the solubility of salicylic acid least in water?

60°C Signup and view all the answers

What is the solubility of salicylic acid in carbon tetrachloride (CCl4) at 25°C?

17.5 mg/mL Signup and view all the answers

Which of the following statements about xylene is correct?

Xylene has a lesser affinity for salicylic acid compared to ethanol. Signup and view all the answers

What form does salicylic acid crystallize into after heating?

Needles Signup and view all the answers

What are the two general steps conducted in the microscale extraction process?

Mixing the two immiscible solutions and separating the layers. Signup and view all the answers

What is the role of the solvents used in the extraction process?

To separate solutes based on their solubility. Signup and view all the answers

What type of mixtures are formed during the solvent extraction process?

Immiscible solutions forming distinct layers. Signup and view all the answers

Which of the following solvents is typically used in extraction due to its low density?

Ether Signup and view all the answers

How are solutes like SA, BA, and sucrose characterized in the extraction process?

Their solubility varies between the two layers. Signup and view all the answers

What is typically determined after conducting the extraction process?

Percentage yield and partition coefficient (Kp). Signup and view all the answers

Why is the density of extraction solvents important?

It influences the separation of layers in the extraction. Signup and view all the answers

What happens to the solutes after extraction in the process?

They get separated into distinct layers. Signup and view all the answers

Study Notes

Experiments Overview

Experiment 1 focused on solvent extraction techniques.
Experiment 2 examined pigment extraction methods.

Solvent Extraction

Extraction Defined: Process of separating a substance from a mixture based on its different solubility in two immiscible liquids.
Liquid-Liquid Extraction: Involves separating compounds dissolved in two different liquids, e.g., using dichloromethane (DCM) and water.
Solid-Liquid Extraction: Involves extracting substances from solid matrices into liquids, e.g., coffee extraction with hot water.

Key Compounds Used

Salicylic Acid (HOC₆H₄COOH)
Benzoic Acid (C₆H₅COOH)
Sucrose (C₁₂H₂₂O₁₁) splits into glucose and fructose upon hydrolysis.

Extraction Methodology

Samples dissolved in a combination of water and ethanol (EtOH).
Utilize ethyl acetate (EtAC) and DCM for separation.
Monitoring extraction involves calculating % yield and distribution coefficients (Kp).

Observations in Extraction

Aqueous and organic layers exhibit clear separation post-extraction.
Two steps: mixing immiscible liquids and separating resulting layers.

Solubility Insights

Solubility of salicylic acid decreases in this order: Ethanol > Ethyl Acetate > Carbon Tetrachloride > Xylene > Water.
High boiling points and cohesive energies of solvents affect their solubility characteristics.

Density of Solvents

Density impacts separation efficiency of organic extracts.
Ethyl acetate has a lower density (0.90 g/mL) compared to DCM (1.33 g/mL).

Troubleshooting Extraction

Emulsions may form, complicating separation. Strategies include “salting out” to enhance separation.
Dark layers can obscure visual identification of interfaces; use of light or funnel tilting aids in clarity.

Considerations for Effective Extraction

Immiscibility between extraction and solution solvents is crucial.
Extraction solvent should possess a high distribution coefficient (Kp) to favor the target component.
Ideal solvents should be easily separable, low in toxicity, and cost-effective.

Pigment Extraction

Conducted using acetone, methanol, and ethanol for sample preparation.
Absorbance measured via spectrophotometry; Beer-Lambert Law relates absorbance to concentration.

Key Calculation in Pigment Extraction

Example provided for determining molar absorptivity from absorbance data.
Absorbance (A) of 1.35 at 750 nm in a 10-mm cuvette requires application of the Beer-Lambert Law for calculations.

Pigment Measurement

Spectrophotometer measures light intensity absorbed by solutions, crucial for assessing pigment concentrations.

Conclusion

Vital techniques in extraction methods include proper solvent selection, solubility understanding, and analytical measurements to ensure efficient and accurate outcomes in both experiments.

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Description

This quiz focuses on the post-laboratory discussions of two experiments: solvent extraction and pigment extraction. You will define key concepts and examples related to liquid-liquid and solid-liquid extraction methods. Test your understanding of these fundamental chemistry techniques.