Avobenzone and dioxybenzone are two commercial sunscreens. Using the principles of solubility, p

step 1 This is the answer to chapter three, problem number 43 from the Smith Organic Chemistry textbook

Avobenzone and dioxybenzone are two commercial sunscreens....

Key Concepts

Like Dissolves Like

This fundamental solubility principle states that substances with similar polarity will tend to dissolve in one another. It means that non-polar substances are more likely to dissolve in non-polar solvents, while polar substances dissolve more readily in polar solvents. In the context of sunscreen, this concept helps predict whether a sunscreen ingredient will wash off in water, which is a polar solvent.

Polarity

Polarity refers to the distribution of electrical charge in a molecule, determining whether the molecule is polar or non-polar. The polarity of a sunscreen component will influence its interaction with water. Polar molecules are attracted to water and hence could dissolve or be displaced by water more easily compared to non-polar molecules, which tend to stick to oily or hydrophobic surfaces.

Hydrophilicity versus Lipophilicity

This concept distinguishes between substances that are attracted to water (hydrophilic) and those that repel water (lipophilic). In sunscreen formulations, hydrophilic ingredients are more prone to washing off in water, whereas lipophilic ingredients are more likely to adhere to the skin or an oily matrix. Understanding this balance helps in predicting the performance of sunscreen ingredients when exposed to water.

Partition Coefficient

The partition coefficient is a quantitative measure of how a compound divides itself between a water phase and an oil phase. It indicates the relative solubility of a substance in water compared to an organic solvent. A compound with a high partition coefficient toward the aqueous phase suggests that it might be more easily washed off by water, making this parameter crucial in evaluating and designing sunscreen formulations for water resistance.

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