Methods of separating and purifying substances 5b 1d 4a

• What is a pure substance?

  A single element or compound not mixed with anything else.
• Mixture

  Consists of two or more elements or compounds not chemically bonded togeather.
• What is a pure substance in everyday language?

  Something that hasn't had anything added to it.
• What is the melting point of a pure substance like?

  In a pure substance, There is only one exact melting and boiling point where all particles of that element begin to melt.
• Why do impure substances and mixtures melt over a range of temperatures?

  Different elements within the substance have different melting points therefore have a range.
• What is chemical analysis?

  The instruments and methods we use to separate, identify, and quantify different substances.
• What is an example of a pure substance?

  Distilled water
• What is a formulation?

  Mixtures that have been prepared using a specific formula.
• What are formulations made from?

  Precise amounts of different components, each component having a particular function.
• Examples of formulations

  Medicines, paints and cleaning agents.
• What is simple distillation used for?

  Seperating a solvent from a solution.
• Why does simple distillation work?

  The dissolved solute has a higher boiling point than the solvent.
• What happens during simple distillation?

  The solution is heating causing the solvent to evaporate from the solution. The gas moves away and is cooled and condensed. The remaining solution becomes more concentrated in solute as amount of solvent decreases.
• What are the steps of simple distillation?

  1. A solution is heated, usually using a Bunsen burner.
  2. The liquid in the mixture evaporates into a gas. 
  3. The gas is cooled by a water jacket, and condenses into a liquid, which then flows into the beaker. 
• What is fractional distillation used for?

  Seperating mixtures of liquids that each have different boiling points.
• What happens during fractional distillation?

  Heat is applied and liquid with lowest boiling point condenses into beaker - If other liquids evaporate, they condense by the fractionating column back into the flask - Temperature is altered and repeat process for the second liquid and repeat process until last liquid is remaining in the flask.
• How would you carry out crystalisation?

  Pour solution into evaporating dish which you heat gently with bunsen burner, Stop heating when crystals begin to form and allow it to cool. Filter out the crystals using filter paper and filter funnel. Lastly, Dry the crystals in a warm oven.
• When do you do crystalisation instead of evaporation?

  For solids more susceptible to thermal decomposition.
• How do you carry out evaporation?

  Pour solution into evaporating dish, place dish on top of tripod, Heat with a Bunsen burner. Solvent should start to evaporate leaving a concentrated solution, Crystals begin to form as the solution is so concentrated and the solvent disappears leaving dry crystals.
• Paper chromotography is the separation of a mixture of soluble substances by running a solvent through the mixture on paper, causing substances to move at different rates over the paper.
• What is chromotography?

  Chemical analysis used to seperates substances from a mixture.
• What is the name for the pencil line?

  The baseline
• Why is pencil used for baseline but not pen?

  Pen would dissolve in the substance and move up.
• The baseline shouldn't be submereged in the solvent
• Which solvents are usually used during chromatography?

  Ethanol and Water
• A substance which is less soluble in the mobile phase will spend more time in the stationary phase, so move slower, and not travel very far up the paper.
• RF value formula = Distance travelled by substance/ distance travelled by colvent