Chemical analysis

• What is a pure substance?

  A pure substance is a single element or compound that is not mixed with any other substance.
• What happens to pure substances at their melting and boiling points?

  Pure substances melt and boil at certain temperatures.
• How can melting point and boiling point data be used in chemistry?

  They can be used to distinguish pure substances from mixtures.
• In everyday language, what does a pure substance mean?

  It refers to a substance that has had nothing added to it, making it unadulterated and in its natural state.
• What is the boiling point of pure water?

  The boiling point of pure water is 100 degrees Celsius.
• What is a formulation?

  A formulation is a mixture that has been designed as a useful product.
• Why are formulations made with carefully measured quantities?

  To ensure that the product has the required properties.
• What are some examples of formulations?

  Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilizers, and foods.
• What is chromatography used for?

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

  The stationary phase and the mobile phase.
• What is the stationary phase in chromatography attracted to?

  The stationary phase is attracted to the paper.
• What is the mobile phase in chromatography attracted to?

  The mobile phase is attracted to the solvent.
• 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?

  Rf = 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.
• Why do smaller, more soluble particles travel further in chromatography?

  They travel further due to differences in solubility and their attractions with the paper.
• What is the method for investigating how paper chromatography can be used to separate colored substances?

  1. Draw a start line in pencil on absorbent paper.
  2. Place samples of 5 different food colorings and an unknown substance on the start line.
  3. Dip the paper into the solvent and wait for it to travel up the paper.
  4. Compare the horizontal spots of the unknown substance with known ones to identify it.
• What should be used to draw the start line in chromatography and why?

  Pencil should be used to draw the start line to avoid dissolving ink affecting the results.
• How is hydrogen tested in a laboratory?

  The test for hydrogen uses a burning splint held at the open end of a test tube of the gas.
• What indicates the presence of hydrogen gas during the test?

  Hydrogen burns rapidly with a pop sound.
• How is oxygen tested in a laboratory?

  The test for oxygen uses a glowing splint inserted into a test tube of the gas.
• What indicates the presence of oxygen gas during the test?

  The glowing splint relights in oxygen.
• How is carbon dioxide tested in a laboratory?

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

  The limewater turns milky (cloudy).
• How is chlorine tested in a laboratory?

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

  The litmus paper is bleached and turns white.
• What is the first test for identifying cations?

  The flame test is the first test for identifying cations.
• What is observed during the flame test for cations?

  Different metal ions produce different colors of visible light.
• What color does barium produce in a flame test?

  Barium produces a light green color in a flame test.
• What color does calcium produce in a flame test?

  Calcium produces a brick red/orange color in a flame test.
• What color does copper produce in a flame test?

  Copper produces a blue/green color in a flame test.
• What color does lithium produce in a flame test?

  Lithium produces a crimson red color in a flame test.
• What color does potassium produce in a flame test?

  Potassium produces a lilac color in a flame test.
• What color does sodium produce in a flame test?

  Sodium produces a yellow/orange color in a flame test.
• What color does magnesium produce in a flame test?

  Magnesium produces no color in a flame test.
• What happens when sodium hydroxide is added to positive ions?

  A precipitate is formed when sodium hydroxide is added to positive ions.
• What color precipitate does copper produce when sodium hydroxide is added?

  Copper produces a blue precipitate when sodium hydroxide is added.
• What color precipitate does iron (ii) produce when sodium hydroxide is added?

  Iron (ii) produces a green precipitate when sodium hydroxide is added.
• What color precipitate does iron (iii) produce when sodium hydroxide is added?

  Iron (iii) produces a brown precipitate when sodium hydroxide is added.
• What color precipitate does magnesium produce when sodium hydroxide is added?

  Magnesium produces a white precipitate when sodium hydroxide is added.