Topic 2 states of matter and mixtures

• filtration

  used to separate an insoluble solid from a liquid
• crystallisation


  used to separate a soluble solid from a solution
• particles in solids

  don't have much energy and are held together in fixed positions by strong forces of attraction
• particles in liquids

  have more energy than those in solids, so can move past each other (but normally stick close together in a random arrangement).

  -forces are attraction are weaker in liquids than in solids
• particles in gases


  particles have more energy than in solids.

  -forces of attraction are very weak, so the gas particles are free to move constantly in random motion
• changes of state

  physical changes so can be undone by heating or cooling a substance
• chemical changes result in what?

  bonds breaking between atoms changing places, so they are difficult to reverse
• pure substance


  made up of only one element or compound

  -melts at a specific temperature
• mixture

  substance that contains two or more compounds or elements

  -melts at a range of temperatures
• simple distillation

  used to separate a liquid from a mixture where the components have large differences in boiling points
• fractional distillation

  used to separate a mixture of different liquids and is useful when the liquids have similar boiling points
• suitable separation method depends on what?

  the properties of the substances in a mixture
• stationary phase

  is a solid or a very thick liquid where the molecules can't move
• mobile phase

  liquid or a gas that carries the molecules over the stationary phase
• Rf value

  the ratio between the distance that a solute travels and the distance travelled by the solvent

  -can be used to analyse the components of a mixture by comparison with the Rf values of known compounds
• chromatography

  used to separate and identify soluble substances from a mixture.

  -pure substances can't be separated out by chromatography so will only produce one spot
• potable water

  (drinkable water) has been treated to make it safe to drink
• process of water purification:

  1.filiration: wire mesh screens out any solid bits

  2. sedimentation: iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom

  3. chlorination: chlorine gas bubbled through to kill harmful bacteria and other microbes
• distilling sea water

  sea water is boiled to produce steam, which is then condensed- this separates the water from the dissolved salts
• water used in analysis is what?

  deionised, as the dissolved ions in normal water could affect the results of an experiment
• look at paper chromatography and simple distillation core practical and answer Rf value questions
• What are the two categories of substances discussed in the study material?

  Metals and non-metals
• How can the properties of metals be explained?

  In terms of metallic structure and bonding
• How many types of bonding are mentioned in the study material?

  Four types
• What are the four types of bonding discussed?

  • Ionic bonding
  • Simple covalent molecular
  • Giant covalent network
  • Metallic bonding
• What occurs during ionic bonding?

  An electron is transferred between atoms
• What is formed as a result of ionic bonding?

  A positive-negative ion pair
• What is the structure of simple covalent molecular substances?

  Small groups of atoms held together
• How are giant covalent networks structured?

  Billions of atoms are held together
• What characterizes metallic bonding?

  Outer electrons are free to move
• What type of structure do ionic compounds form?

  A regular lattice structure
• What is an example of an ionic compound?

  Sodium chloride
• What are the limitations of bonding models?

  • They may not show multiple layers
  • They can oversimplify electron behavior
  • They might not represent real structures accurately
• What do simple molecular substances consist of?

  Atoms joined by strong covalent bonds
• How are molecules in simple molecular substances held together?

  By weak intermolecular forces
• What happens when a simple molecular substance melts or boils?

  Intermolecular forces are broken
• What is an example of a simple molecular substance?

  Water
• What are the key features of ionic compounds?

  • Form regular lattice structures
  • Strong attraction between oppositely charged ions
  • High melting and boiling points
• What are the key features of simple molecular substances?

  • Strong covalent bonds within molecules
  • Weak intermolecular forces between molecules
  • Low melting and boiling points
• What are the key features of giant covalent substances?

  • Billions of atoms held together
  • High melting and boiling points
  • Strong covalent bonds throughout the structure