Chapter 5

• What is the boiling point of pure water?

  $100^\circ \text{C}$
• What is the freezing point of pure water?

  $0^\circ \text{C}$
• What is the density of pure water?

  $1\text{ g cm}^{-3}$
• What happens to water when heat is absorbed?

  • Solid (melting) → Liquid
  • Liquid (evaporation/boiling) → Gas
  • Solid (sublimation) → Gas
• What happens to water when heat is released?

  • Gas (condensation) → Liquid
  • Liquid (freezing) → Solid
  • Gas (sublimation) → Solid
• What is the composition of water in terms of atoms?

  Water is made up of 2 hydrogen atoms and 1 oxygen atom.
• How can the composition of elements in a water molecule be determined?

  Through electrolysis.
• What gas is produced at the anode during electrolysis of water?

  Oxygen gas.
• What gas is produced at the cathode during electrolysis of water?

  Hydrogen gas.
• What is evaporation?


  Evaporation is the process that happens at the surface of water that changes water to water vapour.
• What factors affect the rate of evaporation?

  • Humidity
  • Surrounding temperature
  • Exposed surface area of water
  • Movement of air
• How does the exposed surface area of clothes affect their drying time?

  • Clothes hung on clothes lines have large exposed surface areas.
  • This allows them to dry faster due to increased evaporation.
• How is sea salt obtained?

  Sea salt is obtained from the evaporation of seawater.
• Why can dried seafood be kept longer?

  Because microorganisms cannot survive without water.
• What are the physical characteristics of pure water?

  • Boiling point: \(100^\circ \text{C}\)
  • Freezing point: \(0^\circ \text{C}\)
  • Colourless
  • Density: \(1\text{ g cm}^{-3}\)
• What is a solute?


  A solute is a substance that can dissolve in a liquid.
• What is a solvent?


  A solvent is a liquid that dissolves a substance.
• What is a solution?


  A solution is the mixture formed when a solute dissolves in a solvent.
• What are the characteristics of a dilute solution?

  • Less amount of solute in the solvent
  • Can dissolve more solute
• What are the characteristics of a concentrated solution?

  • More amount of solute in the solvent
  • Can dissolve less solute
• What are the characteristics of a saturated solution?

  • Excess amount of solute in the solvent
  • Cannot dissolve any more solute and forms a precipitate
• How does a solution differ from a suspension?

  A solution is a clear mixture formed when a solute dissolves in a solvent, while a suspension is a cloudy mixture formed from undissolved solute particles in a solvent.
• What is solubility?


  Solubility of a solute is the maximum amount of the solute that can dissolve in 100 ml of solvent at a specific temperature.
• How does temperature affect the rate of solubility?

  The higher the temperature of the solvent, the higher the rate of solubility.
• How does stirring affect the rate of solubility?

  The higher the rate of stirring, the higher the rate of solubility.
• What is a colloid?

  • A mixture of two or more solutes dispersed evenly in a solvent
  • Intermediate between a solution and a suspension
  • Examples: Foam (Shaving cream) & Emulsion (Milk)
• What is considered the universal solvent?

  Water is considered the universal solvent.
• Why is water referred to as a universal solvent?

  Water dissolves almost all substances, including solids, liquids, or gases.
• Give an example of how water acts as a universal solvent.

  Water dissolves detergents used in the cleaning process.
• What are organic solvents?

  • Carbon-based solvents
  • Used to dissolve solutes that are insoluble in water
  • Examples: Alcohol, Kerosene, Acetone, Turpentine, Ether
• Name an example of an organic solvent.

  Alcohol
• What is the purpose of organic solvents?

  Organic solvents are used to dissolve solutes that are insoluble in water.