Question

Which solvent, water or hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\), would you choose to dissolve each of the following? a. \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) d. \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{CH}_{2} \mathrm{OH}\) b. \(\mathrm{CS}_{2}\) e. \(\mathrm{HCl}\) c. \(\mathrm{CH}_{3} \mathrm{OH}\) f. \(\mathrm{C}_{6} \mathrm{H}_{6}\)

Short answer

a. Water d. Hexane b. Hexane e. Water c. Water f. Hexane

Step-by-step solution

Identify the polarity of solvents

Water is a polar solvent, as oxygen is more electronegative than hydrogen, leading to a partial negative charge on oxygen and a partial positive charge on hydrogen atoms. Hexane, on the other hand, is a nonpolar solvent comprised of carbon and hydrogen atoms only, with minimal differences in electronegativity, and therefore no significant positive or negative charges on the molecule.

Identify the polarity of each compound

a. Copper nitrate (Cu(NO₃)₂) is a polar compound as it contains ionic bonds between copper (Cu²⁺) and nitrate (NO₃) ions. d. CH₃(CH₂)₁₆CH₂OH is a large nonpolar hydrocarbon with a small polar hydroxyl (-OH) group at the end, so it's mostly nonpolar. b. Carbon disulfide (CS₂) is a nonpolar compound as both carbon and sulfur have similar electronegativities, and there is no charge separation within the molecule. e. Hydrogen chloride (HCl) is a polar compound due to the electronegativity difference between hydrogen and chlorine atoms, leading to a partial positive charge on hydrogen and a partial negative charge on chlorine. c. Methanol (CH₃OH) is a polar compound due to the electronegativity difference between oxygen and hydrogen atoms in the hydroxyl group. f. Benzene (C₆H₆) is a nonpolar compound comprising carbon and hydrogen atoms only, with no significant electronegativity difference.

Determine which solvent would be a better choice

a. For Cu(NO₃)₂, choose water as the solvent because both are polar. d. For CH₃(CH₂)₁₆CH₂OH, choose hexane as the solvent because the molecule is mostly nonpolar. b. For CS₂, choose hexane as the solvent because both are nonpolar. e. For HCl, choose water as the solvent because both are polar. c. For CH₃OH, choose water as the solvent because both are polar. f. For C₆H₆, choose hexane as the solvent because both are nonpolar.

Key concepts

Polar and Nonpolar Compounds

Understanding the difference between polar and nonpolar compounds is crucial in chemistry. This distinction often determines how substances interact with each other.

Polar compounds have molecules that possess distinct regions of positive and negative charge. This occurs due to differences in electronegativity between atoms, such as in water (H₂O) where the oxygen atom is more electronegative than hydrogen. This imbalance creates a dipole moment, leading to one side of the molecule being more positive and the other more negative.

On the other hand, nonpolar compounds have molecules with symmetrical charge distribution, resulting in no distinct positive or negative regions. In nonpolar molecules such as hexane (C₆H₁₄) or benzene (C₆H₆), the atoms have similar electronegativities and share electrons more equally. This lack of poles means these compounds can share electrons freely, without tugging them towards one side.

Knowing whether a compound is polar or nonpolar helps predict how it will behave in solutions, especially when deciding which solvent to use.

Solubility in Chemistry

Solubility is a key concept in chemistry that describes how well a substance dissolves in a solvent. The principle "like dissolves like" usually applies, meaning that polar substances tend to dissolve well in polar solvents and nonpolar substances dissolve well in nonpolar solvents.

This principle can be observed when trying to dissolve ionic compounds such as copper nitrate (Cu(NO₃)₂) in water. Because both are polar, the water molecules interact with the charged particles in copper nitrate, making it soluble.

Conversely, nonpolar solvents, such as hexane, are effective at dissolving other nonpolar substances, like carbon disulfide (CS₂) or benzene (C₆H₆). These substances have similar molecular structures that allow them to combine without strong attractions to polar molecules or ions.

Understanding solubility is vital for predicting reactions and behaviors of substances in natural and controlled environments. Whether you’re working in the lab or cooking a meal, knowing what dissolves in what can be extremely useful.

Solvent Selection

Choosing the right solvent is essential in many chemical processes, whether in research, industry, or daily applications. Solvent selection is mainly guided by the polarity of both the solvent and the solute involved.

For example, polar solvents like water are excellent at dissolving other polar solutes or ionic compounds due to their ability to stabilize different charges. When dealing with a substance like methanol (CH₃OH), which is polar, water is an effective solvent.

Meanwhile, nonpolar solvents like hexane work best with nonpolar solutes since there's no attraction to polar molecules to disrupt their structure. This is why nonpolar compounds like CH₃(CH₂)₁₆CH₂OH or benzene dissolve well in hexane.

In scenarios where the solute can have both polar and nonpolar characteristics, the dominant portion of the molecule usually dictates the best solvent choice. For instance, long-chain alcohols with a nonpolar body and a polar head might be better dissolved in a nonpolar solvent.

Solvent selection is not always straightforward, but recognizing the relationship between solute and solvent polarity helps guide effective decision-making in practical applications.