Organic Chemistry MCAT Practice Exam

How is the eluting strength of a solvent related to its polarity?

1. More polar solvents have weaker eluting strength.

2. Higher polarity generally increases eluting strength.

3. Non-polar solvents are stronger for elution.

4. Eluting strength is unaffected by polarity.

The correct answer is: Higher polarity generally increases eluting strength.

Polarity plays a significant role in determining the eluting strength of a solvent in techniques such as thin-layer chromatography (TLC) or column chromatography. Elution strength refers to the ability of a solvent to displace or carry compounds as they interact with a stationary phase. Higher polarity solvents typically exhibit increased eluting strength because they can better solvate polar compounds, leading to stronger interactions with the stationary phase. This effectively helps to break the attractions between the compounds and the stationary phase, allowing the polar compounds to be eluted more efficiently. Solvents with high polarity can disrupt hydrogen bonds or other polar interactions present in the stationary phase, facilitating the movement of substances through the column or across the plate. Alternative options point toward misunderstandings of how elution works. For instance, non-polar solvents do not effectively elute polar compounds as they do not provide sufficient interaction or solvation, thus promoting the idea that increased polarity translates to a better elution process. Choosing a solvent with compatible polarity to the compounds is crucial for effective separation.