Chemical analysis

• What is a pure substance in chemistry?

  A pure substance is a single element or compound, not mixed with any other substance.
• How can melting point and boiling point data be used in chemistry?

  They can be used to distinguish pure substances from mixtures.
• What does the term "pure substance" mean in everyday language?

  It refers to a substance that has had nothing added to it, making it unadulterated.
• How should students use melting point and boiling point data?

  Students should use this data to distinguish pure from impure substances.
• What is a formulation in chemistry?

  • A mixture designed as a useful product
  • Each chemical has a specific purpose
  • Components are mixed in measured quantities
  • Examples: fuels, cleaning agents, paints, medicines, alloys, fertilizers, foods
• What should students be able to identify regarding formulations?

  Students should be able to identify formulations given appropriate information.
• What is the purpose of chromatography?

  Chromatography is used to separate mixtures and identify substances.
• What are the two phases involved in chromatography?

  The stationary phase and the mobile phase.
• How does separation in chromatography depend on the substances?

  Separation depends on the distribution of substances between the stationary and mobile phases.
• What is the formula for calculating the Rf value in chromatography?

  $R_f =$$\frac{distance\ moved\ by\ substance}{distance\ moved\ by\ solvent}$
• What does a pure compound produce in chromatography?

  A pure compound will produce a single spot in all solvents.
• How can chromatographic methods be used in chemistry?


  They can be used for distinguishing pure substances from impure substances.
• What can be interpreted from chromatograms?

  Students should be able to interpret chromatograms and determine Rf values from them.
• What is the test for hydrogen gas?

  The test for hydrogen uses a burning splint held at the open end of a test tube of the gas.
• What happens when hydrogen burns in the test?

  Hydrogen burns rapidly with a pop sound.
• What is the test for oxygen gas?

  The test for oxygen uses a glowing splint inserted into a test tube of the gas.
• What happens to a glowing splint in the presence of oxygen?

  The splint relights in oxygen.
• What is the test for carbon dioxide gas?

  The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water).
• What happens when carbon dioxide is bubbled through limewater?

  The limewater turns milky (cloudy).
• What is the test for chlorine gas?

  The test for chlorine uses damp litmus paper.
• What happens to damp litmus paper in chlorine gas?

  The litmus paper is bleached and turns white.
• What can flame tests identify?

  Flame tests can identify some metal ions (cations).
• What color flame does lithium compounds produce in flame tests?

  Lithium compounds result in a crimson flame.
• What color flame does sodium compounds produce in flame tests?

  Sodium compounds result in a yellow flame.
• What color flame does potassium compounds produce in flame tests?

  Potassium compounds result in a lilac flame.
• What color flame does calcium compounds produce in flame tests?

  Calcium compounds result in an orange-red flame.
• What color flame does copper compounds produce in flame tests?

  Copper compounds result in a green flame.
• What happens to flame colors when a mixture of ions is used?

  Some flame colors can be masked.
• What can sodium hydroxide solution identify?

  Sodium hydroxide solution can be used to identify some metal ions (cations).
• What precipitates form when sodium hydroxide is added to solutions of aluminium, calcium, and magnesium ions?

  They form white precipitates.
• Which aluminium hydroxide precipitate behavior is unique when sodium hydroxide is added?

  Only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.
• What colored precipitates do copper(II), iron(II), and iron(III) ions form with sodium hydroxide?

  Copper(II) forms a blue precipitate, iron(II) a green precipitate, and iron(III) a brown precipitate.
• What do carbonates react with to produce carbon dioxide gas?

  Carbonates react with dilute acids.
• How can carbon dioxide be identified?

  Carbon dioxide can be identified with limewater.
• What do halide ions produce with silver nitrate solution?

  Halide ions produce precipitates with silver nitrate solution in the presence of dilute nitric acid.
• What are the colors of precipitates formed by halide ions with silver nitrate?

  Silver chloride is white, silver bromide is cream, and silver iodide is yellow.
• What do sulfate ions produce with barium chloride solution?

  Sulfate ions produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
• What are the advantages of instrumental methods in chemistry?

  • Accurate
  • Sensitive
  • Rapid
• What is flame emission spectroscopy used for?

  Flame emission spectroscopy is used to analyze metal ions in solutions.
• How does flame emission spectroscopy work?

  The sample is put into a flame, and the light given out is passed through a spectroscope.