MCAT extraction and chromatography practice questions

What is liquid-liquid extraction?

A technique used to separate compounds based on their solubility in two immiscible liquids.

True or False: A polar compound is better extracted using a nonpolar solvent.

False. Polar compounds are better extracted using polar solvents due to solubility.

List two common solvents in extraction.

1. Water 2. Ethyl acetate

What is the purpose of a drying agent?

To remove trace amounts of water from organic solutions, improving yield.

Fill in the blank: The __________ phase in extraction is where the target compound is located.

organic

Describe the role of pH in acid-base extraction.

pH alters the ionization state of compounds, enhancing separation efficiency.

Compare simple extraction to fractional extraction.

Simple extraction uses one solvent; fractional uses multiple stages for better separation.

What is the function of a separatory funnel?

To facilitate the separation of two immiscible liquids by decanting.

Cause → Effect: What happens when a base is added to a mixture of acid and its salt?

The acid converts to its free base form, increasing solubility in organic phase.

What is the significance of partition coefficient?

It quantifies the distribution of a compound between two phases, guiding extraction choice.

True or False: Increasing the volume of solvent always improves extraction efficiency.

False. Excessive volume can lead to dilution and decrease efficiency.

Explain the term 'back extraction.'

A technique where the extracted compound is re-extracted into a new solvent for purification.

What is an example of solid-liquid extraction?

Brewing coffee involves extracting soluble compounds from coffee grounds.

List the steps of liquid-liquid extraction.

1. Mix two solvents 2. Separate phases 3. Collect layers 4. Dry organic layer

Fill in the blank: The __________ solvent should have a higher density than the aqueous phase.

organic

What type of compounds does Soxhlet extraction target?

Soluble compounds in solid matrices, often used for natural products.

Define solubility product (Ksp) in the context of extraction.

Ksp relates to the maximum concentration of solute that can dissolve in a solvent.

True or False: Heating the mixture can enhance extraction efficiency.

True. Heating increases solubility and speeds up the extraction process.

What is the ultimate goal of extraction?

To isolate a desired compound from a mixture for further analysis or use.

How does temperature affect extraction?

Increased temperature may enhance solubility and diffusion, improving yield.

What is chromatography?

A technique for separating mixtures based on different interactions with a stationary phase and a mobile phase.

True or False: Chromatography can only separate liquid samples.

False - Chromatography can separate gases and solids as well.

Define stationary phase in chromatography.

The phase that remains fixed in place; typically a solid or a viscous liquid.

List two common types of chromatography.

1. Thin Layer Chromatography (TLC) 2. High-Performance Liquid Chromatography (HPLC)

Define mobile phase in chromatography.

The mobile phase is the solvent that carries the sample through the stationary phase, facilitating separation based on interactions.

True or False: Thin-layer chromatography (TLC) requires large sample sizes.

False. TLC is ideal for small sample sizes, making it efficient for preliminary analysis.

What does Rf stand for in chromatography?

Rf (retention factor) is the ratio of the distance traveled by the compound to the distance traveled by the solvent front.

Compare column chromatography and high-performance liquid chromatography (HPLC).

Column chromatography is slower and less precise than HPLC, which provides higher resolution and speed due to increased pressure.

Fill in the blank: In gas chromatography, compounds are separated based on their _______.

Boiling points and vapor pressures.

Cause → Effect: Increasing the polarity of the mobile phase in reversed-phase chromatography.

Leads to increased elution of non-polar compounds, enhancing separation.

What principle does size-exclusion chromatography rely on?

It separates molecules based on size, allowing larger molecules to elute first while smaller ones are retained.

True or False: Paper chromatography can analyze ionic compounds effectively.

False. Paper chromatography is not suitable for ionic compounds due to their solubility issues.

Describe the role of temperature in gas chromatography.

Higher temperatures reduce viscosity and volatility, allowing samples to vaporize and separate more efficiently.

What is the main advantage of using HPLC?

HPLC allows for the separation of complex mixtures with high resolution and speed, suitable for detailed analysis.

Define affinity chromatography.

A technique that separates biomolecules based on specific interactions, such as antibody-antigen binding.

List two common stationary phases used in chromatography.

- Silica gel - Alumina

What is the purpose of a guard column in HPLC?

To protect the main column from contaminants and extend its lifespan by trapping particulate matter.

Fill in the blank: The principle of liquid-liquid chromatography involves _______.

Partitioning of compounds between two immiscible liquids.

True or False: Normal-phase chromatography uses a non-polar stationary phase.

True. Normal-phase chromatography employs a polar stationary phase with non-polar solvents.

What equation relates retention time to the efficiency of a chromatography column?

$\displaystyle N = 16\\frac{t_R^2}{w^2}$, where $\displaystyle N$ is the number of theoretical plates, $\displaystyle t_R$ is retention time, and $\displaystyle w$ is peak width.