Atomic structure and periodic table

• Showing what's happening in a chemical reaction

  1. Understand chemical equations

  2. Use a word equation

  3. Use a symbol equation
• Word equation

  Shows the reactants on the left and the products on the right, with an arrow in the middle
• Reactants

  The molecules that react together
• Products

  The molecules that are produced
• Symbol equation

  Uses the chemical symbols of each molecule involved
• Oxygen exists as a molecule made up of two atoms, so it is written as O2
• Balancing a chemical equation

  1. Ensure the total number of each type of atom is the same on both sides of the arrow

  2. Can't change the little numbers, only the big numbers in front of elements/compounds

  3. Need to keep whole numbers
• When balancing, it's recommended to balance the least common elements first
• In today's video we're going to look at how we can separate both soluble and insoluble solids from liquids using techniques such as filtration, evaporation and crystallization
• Mixture

  A liquid and an insoluble solid
• Solution

  A liquid and a soluble solid, where the solid is the solute and the liquid is the solvent
• Filtration

  1. Place filter paper with tiny holes in a filter funnel

  2. Pour the mixture through, leaving the insoluble solid behind on the paper
• Filtration cannot separate a soluble solid from a liquid
• Evaporation

  1. Place the solution in an evaporating dish or crucible

  2. Slowly heat with a Bunsen burner

  3. Solvent evaporates, leaving behind concentrated solution and eventually dry crystals
• Evaporation

  • Relatively quick and easy
  • Some solids may thermally decompose
• Crystallization

  1. Place solution in evaporation dish

  2. Heat gently, e.g. using a water bath

  3. Stop heating once crystals start to form

  4. Filter out the crystals

  5. Dry the crystals
• Crystallization

  • Slower than evaporation
  • Avoids thermal decomposition of solids
• Solids are less soluble at colder temperatures
• Simple distillation

  Used for separating out a liquid from a solution, e.g. separating pure water from seawater
• Simple distillation

  1. Heat the mixture so the liquid evaporates

  2. Vapour passes through condenser where it cools and condenses into liquid

  3. Liquid collects in beaker
• Equipment for simple distillation

  • Flask containing the liquid mixture
  • Thermometer to measure temperature
  • Condenser with water jacket for cooling
  • Beaker to collect the pure liquid
  • Heating device like a Bunsen burner
• Simple distillation doesn't work for separating liquids with similar boiling points
• Fractional distillation

  Main technique used for separating mixtures of liquids with similar boiling points
• Fractional distillation

  1. Vapours pass through a fractionating column

  2. Column is cooler at the top than bottom

  3. Vapours condense at different heights in the column based on boiling points

  4. Separate pure liquids collected
• Fractionating column

  • Contains glass rods to provide high surface area
  • Cooler at the top than bottom
• Liquids separated by fractional distillation

  • Methanol
  • Ethanol
  • Propanol
• Methanol has the lowest boiling point

  It evaporates first and passes through the column
• Ethanol and propanol have higher boiling points

  They condense back into the flask as they rise up the cooler column
• The only liquid that passes through the column is pure methanol
• Repeating the process for ethanol and propanol

  1. Raise temperature to boil off ethanol

  2. Raise temperature again to boil off propanol