Solubility of Compounds Experiment

Purpose

• Predict which of two solvents can solubilize various solutes based on solute-solvent interactions.

Key Concepts

• Electronegativity: Tendency of an atom to attract electrons in a bond.
• Intermolecular Forces: Forces that mediate interaction between molecules. Key types include:
  • London Dispersion Forces (Van der Waals)
  • Dipole-Dipole Interactions
  • Hydrogen Bonds
• Solute-Solvent Interactions: Determines solubility based on intermolecular force similarity.
• Polarity: A molecule is polar if it contains polar bonds and has a net dipole moment.

Intermolecular Forces Detailed

London Dispersion Forces

• Arise from instantaneous dipoles caused by electron movement.
• Weakest intermolecular force but significant enough for many compounds to exist as liquids or solids at room temperature.
• Example: Formation of induced dipoles in argon (Figure 1).

Dipole-Dipole Interactions

• Occur between molecules with permanent dipoles, arising from differences in electronegativity.
• Stronger than London forces.
• Example: HCl (polar) vs Cl2 (nonpolar) (Figure 2).
• Molecular Polarity: Depends on both electronegativity difference and molecular geometry.
  • Example: CCl4 is nonpolar despite polar C-Cl bonds due to symmetrical arrangement, while CHCl3 is polar due to its geometry (Figure 3).

Hydrogen Bonds

• Form when hydrogen is bonded to highly electronegative atoms like F, O, N, resulting in strong dipole interaction.
• An example is water molecules forming hydrogen bonds (Figure 4).

Solubility Principle

• "Like dissolves like": Polar solvents dissolve polar solutes, while non-polar solvents dissolve non-polar solutes. Similarity in intermolecular forces leads to solubility.
• Figure 5 illustrates solubility due to similar intermolecular forces.

Intermolecular Interactions in Ionic Compounds

• Ionic compounds dissociate into cations and anions in a solvent.
• Ion-Dipole Interactions: Strong interactions between ions and polar solvent molecules, enhancing solubility in polar solvents like water (Figure 6).

Example: Solubility Predictions

• Compounds: Pentane (C5H12), Ethanol (C2H5OH), Potassium Hydroxide (KOH)

1. Ethanol (C2H5OH)

• Exhibits London, dipole-dipole interactions, and hydrogen bonding due to the presence of O.
• Highly soluble in polar solvents.

2. Pentane (C5H12)

• Forms only London dispersion forces due to non-polar nature.
• Soluble in non-polar solvents such as hexane.

3. Potassium Hydroxide (KOH)

• An ionic compound that dissociates in solution, soluble in polar solvents due to ion-dipole interactions.

Experimental Procedure Notes

Safety Notes

• Prevent skin and eye contact with chemicals.
• Dispose of waste properly.
• Report any accidents to your instructor.

Experimental Steps

1. Predict solubilities of various compounds (e.g., octane, toluene, acetonitrile) in either water or 1-decene based on intermolecular interactions.
2. Test predictions by mixing solutes and solvents in test tubes.
3. Record observations to validate or revise predictions based on actual solubility results.

Conclusion

• Analyze a successful solute-solvent pairing, detailing intermolecular forces that confirmed solubility and explaining why another solvent was less suitable.
• The interactions between solute and solvent dictate the solubility outcomes, emphasizing the importance of understanding intermolecular forces in predicting solubility behavior.