Chapter 12:

• Carbon dioxide:

  Test: Bubble through lime water

  Result: Lime water goes cloudy if carbon dioxide is present
• Oxygen:

  Test: Glowing splint

  Result: Relights if oxygen is present
• Hydrogen:

  Test: Lit splint

  Result: Sqeaky pop is hydrogen is present
• Chlorine:

  Test: Blue litmus paper

  Result: Bleached (goes from blue to white) if chlorine is present
• A pure substance is one that is made up of just one substance. This substance can be an element or a compound.
• A pure substance has a specific fixed melting point
• Melting and boiling point data can be used to distinguish pure substances from mixtures
• If a substance melts over a range of temperatures it is impure. A pure substance will melt at a fixed temperature.

  An impure substance has different elements so will have a range of melting points.
• A formulation is a mixture that has been designed as a useful product e.g. medicines, paint, washing up liquid
• Formulations are made by mixing the components in carefully measured quantities to ensure that the product has useful required properties
• Chromamtography is used to separate substances in a mixture
• Solvent-the liquid in which the solute dissolves to form a soultion
• Mobile phase- phase in chromatography that moves, usually a solvent or mixture of solvents
• Stationary phase- phase in chromatography that does not move, for instance, the paper in chromatography
• The start line is drawn in pencil as it is insoluble so will not affect the results
• The inks shouldn't touch the solvent because the inks would comtaminate the results.
• Retention factor (Rf)= distance moved by substance / distance moved by solvent
• If multiple colour show the substance is impure
• Why calculate the Retention factor, Rf?

  • It allows us to identify the substances we have found by comparing them with a database
  • The larger the Rf value, the more soluble the substance is