Solutions and solubility | Year 8 Chemistry (Cambridge) PDF Download

Introduction to Solutions

• Solutions are homogeneous mixtures composed of a solvent and one or more solutes.
• The solvent is the substance in which the solute dissolves, forming a uniform mixture.

Concentration of Solutions

• Molarity (M): Molarity is defined as the number of moles of solute per liter of solution (mol/L).
• Example: A solution with 0.5 M concentration means there are 0.5 moles of solute in 1 liter of solution.

Factors Affecting Solubility

• Temperature: Generally, solubility increases with temperature for solids and decreases for gases.
  • Example: Sugar dissolves faster in hot tea compared to cold tea.
• Pressure: Affects mainly gases; higher pressure increases solubility.
  • Example: Carbon dioxide is more soluble in soda under pressure.

Solubility and Saturated Solutions

• Saturated Solution: Contains the maximum amount of solute that can dissolve at a given temperature.
  • Example: A solution of sugar in water where no more sugar can dissolve at a specific temperature.
• Supersaturated Solution: Holds more solute than normally possible at a given temperature, achieved by careful cooling of a saturated solution.
  • Example: Creating a supersaturated sugar solution by heating and then slowly cooling it.

Solubility Units

• Molality (m): Molality is the number of moles of solute per kilogram of solvent.
• Example: 1 molal (1 m) solution has 1 mole of solute dissolved in 1 kilogram of solvent.

Factors Affecting Dissolving Rate

• Stirring: Increases the rate by bringing fresh solvent into contact with the solute.
• Temperature: Generally, higher temperatures increase the rate of dissolution for solids in liquids.
• Particle Size: Smaller solute particles dissolve faster due to increased surface area.

Conclusion

Understanding solutions and solubility helps in various applications from chemistry labs to everyday life, such as cooking and cleaning.