Purity, formulations, chromatography

• Cooling curve


  A graph, which plots the temperature of a substance as it cools over time.
• flatline


  when the bonds are re-arranging itself.
• (everyday life) pure substance

  substance that has had nothing added to it. e.g pure milk
• (chemistry) pure substance

  A single element or compound, not mixed with any other substances.
• Every element and compound has its own properties and it melts and boils as specific temperatures.
• uncertainty


  the amount of error your measurements may have.
• Pure substances will always have a definite melting or boiling point.


  Impure substances have a range of melting or boiling points.
• The presence of impurities usually:

  • Lowers the melting point
  • raises the boiling point
• Formulations 


  A complex mixture that has been carefully designed as a useful product in which each chemical has a particular purpose.
• formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
• Examples of formulations:

  • fuels
  • cleaning products
  • paints
  • medicines
  • alloys
  • fertilisers
  • foods
• In paint, the components mixed together include:

  • Pigment: Provides the colour
  • Binder: Creates a film to hold the pigment in place
  • Solvent: dissolves the components and alter the viscosity (the state of being thick and semi-fluid).
• Calpol contains:

  • Paracetamol: Used as a painkiller
  • Glycerol: Improves texture
  • Water: dissolves the chemical in
• Chromatography


  A technique used to separate and identify components in a mixture.
• Mobile phase


  The phase where molecules move usually a liquid or gas. E.g. (In paper chromatography), it would be the water or solvent used.
• Stationary phase


  The phases where the molecules don't move, often a solid or thick liquid. E.g. (In paper chromatography), it would be paper.
• • During chromatography, the solvent moves up and carries the components in the mixture with it.
  • the distance a component moves up depends on the distribution between the mobile and stationary phase.
• Atom


  the smallest part of an element that can exist, which are incredibly small and makes up everything in the universe.
• Element


  A substance made up of one type of atom and cannot be broken down into simpler substances by chemical means.
• Compound


  substances that form when two or more elements react and their atoms chemically combine in a fixed ratio by mass.
• Mixture


  A physical combination of two or more substances that aren't chemically joined.
• Molecules


  A cluster of non-metal atoms that are chemically bonded together.
• Solute


  A solid that dissolves
• Solvent


  A liquid that does the dissolving
• Solution


  formed when a solute completely dissolves in a solvent
• soluble


  if a solute dissolves in a solvent then its...
• insoluble


  when a solute doesn't dissolve in a solvent then its...
• 1. The more soluble a component is in the solvent, the more time it would spend in the mobile phase, which means it will travel further up.

  2. The more attracted a component is to the paper, the more time it would spend in the stationary phase, meaning it will NOT travel as far up.

  
• The CHROMATOGRAM will show the different components in the mixture:

  • The number of SPOTS observed tells you the number of COMPONENTS in the mixture.
  • If there is only ONE SPOT on the chromatogram, the original sample is a PURE SUBSTANCE.
  • If the sample does NOT MOVE, it is INSOLUBLE in the solvent.

  A) 3 components in the sample

  B) pure sample

  C) sample is insoluble

  
• Rf Values


  Values used to identify the components within a mixture.
• Rf values equations:

  A) substance

  B) solvent

  
• The ink has 3 DYES, two are known and one is unknown.

  The components with the same heights have the same Rf values, so are the same substances.

  Therefore, the ink contains DYE 1 and DYE 2 but does NOT contain DYE 3, as it is at a completely different height to the others.

  
• Method for Chromatography:

  1. Draw a PENCIL LINE near the bottom of the chromatography paper.
  2. Place dots of KNOWN DYE COLOURS and a dot of the INK being investigated.
  3. Place the bottom of the paper IN THE SOLVENT, making sure the pencil line is ABOVE the solvent.
  4. The solvent will move up the paper, taking the substances with it.
  5. Before the solvent reaches the top, remove the paper and let it dry to see the CHROMATOGRAM.
  6. Compare the positions of the dots on the KNOWN DYES to those of the INK.

  
• substances that are very soluble will travel a long way up the chromatogram and will have larger Rf values.
• substances that are attracted to the stationary phase will not travel far and will have smaller Rf values.
• Mixture


  A substance that produces two or more spots.
• The distance is different for each substance.
• Filtration


  separates insoluble solids from a liquid
• crystallisation


  evaporates a solvent, leaving the solute.
• simple distillation


  separates solvent from a solution as long as the solvent has a lower boiling point than the solute.