Solubility – What Dissolves in Water?

📚 Key Concepts

🔹 Understanding Solubility

Solubility is the ability of a material to dissolve completely in water, forming a uniform mixture.

image

Key Terms:

  • Solute: The substance that dissolves (sugar, salt)
  • Solvent: The substance that does the dissolving (water)
  • Solution: The uniform mixture formed (sugar water, salt water)

🔹 Soluble Materials

Materials that dissolve completely in water are called soluble materials.

image

Common Soluble Materials:

  • Sugar – completely dissolves, sweetens water
  • Salt – completely dissolves, makes water salty
  • Lemon juice – mixes completely with water
  • Honey – dissolves slowly but completely
  • Baking soda – dissolves completely
  • Coffee powder – dissolves to make coffee
  • Food coloring – dissolves and colors water

Characteristics of Dissolution:

  • Material disappears from view
  • Solution becomes uniform
  • Cannot be separated by simple filtration
  • Properties of water change (taste, color, etc.)

🔹 Insoluble Materials

Materials that do not dissolve in water are called insoluble materials.

Common Insoluble Materials:

  • Sand – settles at bottom
  • Chalk powder – makes water cloudy
  • Sawdust – floats on surface
  • Oil – forms separate layer
  • Plastic pieces – remain unchanged
  • Stone chips – sink to bottom
  • Wax – floats as solid pieces

Characteristics of Insoluble Materials:

  • Remain visible in water
  • Can be separated by filtration
  • Do not change water’s basic properties
  • May float, sink, or remain suspended

🔹 Factors Affecting Solubility

1. Temperature:

  • Hot water dissolves more sugar than cold water
  • Heat increases molecular movement
  • Most solids dissolve better in hot water

2. Stirring:

  • Increases rate of dissolution
  • Brings fresh solvent to solute surface
  • Does not increase total amount that can dissolve

3. Particle Size:

  • Smaller particles dissolve faster
  • More surface area exposed to solvent
  • Powdered sugar dissolves faster than crystal sugar

4. Nature of Materials:

  • Some materials are naturally more soluble
  • Chemical structure determines solubility
  • “Like dissolves like” principle

🔹 Partial Solubility

Some materials dissolve partially:

  • Flour – some dissolves, some remains suspended
  • Mud – small particles remain suspended
  • Milk powder – dissolves but may leave residue

🔹 Applications of Solubility

In Cooking:

  • Dissolving sugar in tea/coffee
  • Adding salt to curry
  • Making lemonade with sugar and lemon
  • Dissolving spices in water

In Medicine:

  • Dissolving tablets in water
  • Making ORS (Oral Rehydration Solution)
  • Liquid medicines use solubility

In Cleaning:

  • Soap dissolves in water for cleaning
  • Detergents dissolve dirt and grease
  • Stain removers use solubility principles

In Industry:

  • Purification processes
  • Chemical manufacturing
  • Food processing
  • Paint and dye making

🔹 ORS – A Life-Saving Application

Oral Rehydration Solution (ORS):

  • Used to treat dehydration
  • Contains sugar and salt dissolved in water
  • Available in ready-made packets
  • Can be made at home: 6 teaspoons sugar + ½ teaspoon salt in 1 liter boiled water

Why ORS Works:

  • Sugar provides energy
  • Salt replaces lost electrolytes
  • Water rehydrates the body
  • All dissolve completely for easy absorption