chemical analysis

• What defines a pure substance in chemistry?

  Contains a single element or compound
• What happens to pure substances at specific temperatures?

  They melt and boil at specific temperatures
• What characterizes an impure substance?

  Contains more than one type of element or compound
• How do impure substances behave when heated?

  Melt and boil at a range of temperatures
• What is matter defined as?

  Any substance that occupies space and has mass
• What is a mixture in chemistry?

  A combination of two or more pure substances
• What is a homogeneous mixture?

  Has uniform composition and properties throughout
• What is a heterogeneous mixture?

  Has non-uniform composition and varying properties
• What defines pure substances in terms of composition?

  Has a defined and constant composition
• What is an element made up of?

  Atoms that each have the same atomic number
• What is a compound composed of?

  A combination of atoms or ions in a fixed ratio
• What are formulations in chemistry?

  Examples of mixtures with specific proportions
• Why do scientists work on formulations?

  To get the right components in useful proportions
• What methods can be used to separate mixtures?

  • Filtration: separates insoluble solids from liquids
  • Crystallisation: evaporates solvent leaving solute
  • Simple distillation: separates solvent from solution
  • Fractional distillation: separates substances from liquid mixtures
• What is chromatography used for?

  To separate different components in a mixture
• How can you test for the presence of gases?

  • Hydrogen: Hold lighted splint, hear squeaky pop
  • Oxygen: Hold glowing splint, splint re-lights
  • Carbon dioxide: Bubble through limewater, turns cloudy white
  • Chlorine: Hold damp litmus, bleaches litmus white
• What happens when you hold a lighted splint near hydrogen gas?

  You hear a squeaky pop
• What occurs when a glowing splint is held near oxygen gas?

  The splint re-lights
• What is the result of bubbling carbon dioxide through limewater?

  The limewater turns cloudy white
• What happens when damp litmus is held near chlorine gas?

  It bleaches the litmus white