Lecture Notes: Polarity and Solubility

Introduction

• Polarity: Concept of having charge(s).
  • Polar molecule: Has charge or charges.
  • Nonpolar molecule: Does not have a charge.
• Example: Water is a polar molecule with hydrogen (delta positive) and oxygen (delta negative) forming a dipole.

Solubility

• Definition: Ability of a substance to dissolve in a solvent.
• Importance: Linked with polarity; focus primarily on water as a solvent.

Experiment with Salt and Oil

• Salt in Water:
  • Salt (sodium chloride) dissolves in water.
  • Disappears into the solution indicating solubility.
• Oil in Water:
  • Forms a layer on top; does not dissolve.

Factors Affecting Solubility

• Water's Dipole Nature:
  • Partially positive and negative charges of water affect solubility.
• Salt (Sodium Chloride):
  • Contains sodium (positive) and chloride (negative) ions.
  • Interacts with water due to polarity.
  • Sodium interacts with water's negative side, chloride with positive side.
  • This interaction leads to salt being hydrophilic (water-loving) and soluble.
• Oil:
  • Nonpolar, lacks charge.
  • Water cannot form interactions with oil; oil forms a separate layer.
  • Hydrophobic nature (water-hating) leads to insolubility.

Summary of Concepts

• Polar Molecules:
  • Interact and dissolve in water (e.g., sugars, amino acids, salts like sodium chloride).
• Nonpolar Molecules:
  • Do not dissolve in water (e.g., oils, fats, polysaccharides).

Special Cases

• Alpha Glucose vs. Starch:
  • Alpha glucose is soluble.
  • Starch (amylose) is insoluble despite both being carbohydrates.

Key Takeaways

• Solubility in water largely depends on the polarity of the substance.
• Understanding the interaction between solute and solvent is crucial for predicting solubility.