C12 - Chemical analysis

• What is meant by purity in chemistry?

  A pure substance has nothing added to it.
• What defines a pure substance?

  A pure substance consists of only one substance.
• What are the two types of pure substances?

  Elements and compounds
• How do melting and boiling points relate to purity?

  They are specific for pure substances.
• How do impurities affect melting and boiling points?

  Impurities lower melting points and raise boiling points.
• What is the melting point range of purified caffeine?

  234-237 °C
• What does a wider melting point range indicate?

  It indicates an impure sample.
• What is a formulation in chemistry?

  • A mixture designed for a useful product
  • Contains specific proportions of components
  • Examples include medicinal drugs and paints
• What percentage of active drug do medicinal drugs typically contain?

  5% to 10%
• What are the components of paint formulations?

  Pigment, binder, and solvent
• What is the role of a surfactant in cleaning agents?

  It removes grease from surfaces.
• What is the purpose of a rinse agent in washing up liquids?

  To help water drain off crockery.
• What is the difference between pure in advertising and in chemistry?

  Advertising may imply purity, while chemistry defines it.
• What is the melting range of the white powder in the experiment?

  158 °C to 169 °C
• What does the melting range of the white powder indicate?

  It suggests the powder is impure.
• Why is oil used instead of water in the melting point apparatus?

  Oil has a higher boiling point than water.
• What is the positive test for hydrogen gas?

  A lighted splint pops.
• How is oxygen gas produced for testing?

  By decomposing hydrogen peroxide with a catalyst.
• What is the positive test for oxygen gas?

  A glowing splint relights.
• What is the positive test for carbon dioxide gas?

  Limewater turns milky.
• What is the positive test for chlorine gas?

  Damp blue litmus paper turns white.
• Why is safety important when testing for chlorine gas?

  Chlorine is a toxic gas.
• What is the purpose of flame tests in chemistry?

  To identify metal ions.
• What are the key points about gases in chemical reactions?

  • Many reactions produce gases.
  • Quick tests exist to identify gases.
  • Each gas has a specific test.
• Why does hydrogen gas 'pop' when a lighted splint is applied?

  It burns rapidly, producing a sound.
• What is the first step in testing for chlorine gas?

  Add concentrated hydrochloric acid to potassium manganate(VII).
• What should be done with damp blue litmus paper during the chlorine gas test?

  Hold it in the mouth of the boiling tube.
• What happens to damp blue litmus paper when exposed to chlorine gas?

  It bleaches the paper white.
• What are the key points for testing gases?

  • Hydrogen gas: 'pops' with a lighted splint.
  • Oxygen gas: relights a glowing splint.
  • Carbon dioxide: turns limewater milky.
  • Chlorine gas: bleaches damp blue litmus paper.
• Why do scientists analyze and identify substances?

  To monitor the environment and ensure safety.
• What is the procedure for conducting a flame test?

  1. Clean nichrome wire loop with hydrochloric acid.
  2. Dip in hydrochloric acid again.
  3. Dip into the metal compound.
  4. Hold in a Bunsen burner flame.
  5. Observe the flame color to identify metal ion.
• What happens if a sample contains a mixture of metal ions during a flame test?

  Some flame colors can be masked.
• What precipitate forms when aluminium, calcium, or magnesium ions react with sodium hydroxide?

  A white precipitate forms.
• What happens to the precipitate formed with aluminium ions when more sodium hydroxide is added?

  It dissolves in excess sodium hydroxide.
• What color flame do calcium ions produce in a flame test?

  Orange-red flame.
• What color precipitate do copper(II) ions produce with sodium hydroxide?

  Blue precipitate.
• What color precipitate do iron(II) ions produce with sodium hydroxide?

  Green precipitate.
• What color precipitate do iron(III) ions produce with sodium hydroxide?

  Brown precipitate.
• How can you identify carbonates in a substance?

  Add dilute acid to produce carbon dioxide.
• What is the reaction when magnesium carbonate is tested with hydrochloric acid?

  Produces magnesium chloride, water, and carbon dioxide.