Chemical Analysis

• Sodium gives a yellow flame
• Calcium gives a red flame
• Expose chlorine gas to damp blue litmus paper. It will turn white.
• Oxygen relights a glowing splint.
• Hydrogen creates a squeaky pop when it reacts with oxygen
• Carbon dioxide turns limewater cloudy when bubbled through it.
• Rf value = distance travelled by the substance ÷ distance travelled by the solvent
• When damp blue litmus paper is exposed to chlorine gas, it turns red, then bleaches white.
• What safety precautions are required for testing chlorine gas?

  • Do the experiment in a fume cupboard
  • Wear a gas mask
• When hydrogen is exposed to a lit splint, there is a squeaky pop.
• How do you test for carbonate ions?

  1. React substance with hydrochloric acid
  2. If it contains carbonate ions, carbon dioxide gas will bubble
  3. Bubble through limewater and see if it turns cloudy
• How do you test for sulfate ions?

  1. React substance with hydrochloric acid to remove any carbonate ions
  2. Add barium chloride solution
  3. If sulfate ions are presents, it will form a white precipitate of barium sulfate
• How do you test for halide ions?

  1. React solution with nitric acid to remove any carbonate or sulfate ions
  2. Add silver nitrate solution
  3. If white precipitate, it contains chloride ions
  4. If cream precipitate, it contains bromide ions
  5. If yellow precipitate, it contains iodide ions
• Antiseptic wipes and the bunsen burner flame are used to clean the platinum wire loop
• Lithium ions burn with a crimson flame
• Sodium ions burn with a yellow flame
• Potassium ions burn with a lilac flame
• Calcium ions burn with an orange-red flame
• Copper ions burn with a green flame
• When copper II reacts with hydroxide ions, it forms a blue precipitate of copper hydroxide.
• When calcium reacts with sodium hydroxide, it forms a white precipitate of calcium hydroxide.
• When iron II reacts with sodium hydroxide, it forms a green precipitate of iron hydroxide.
• When iron III reacts with sodium hydroxide, it forms a brown precipitate of iron hydroxide.
• When magnesium reacts with sodium hydroxide, it forms a white precipitate of magnesium hydroxide.
• Aluminium and sodium hydroxide forms a precipitate that is white at first, but if there is excess NaOH, it then redissolves to form a colourless solution
• When metal ions are heated they start to emit light
• How does flame emission spectroscopy work?

  1. Metal ions are heated until they emit light
  2. Light is detected by a spectroscope which can distinguish between the individual wavelengths of light emitted
  3. Each metal ion emits a unique combination of wavelengths, producing a unique line spectrum.
  4. This allows us to identify an unknown metal cation by comparing its line spectrum to those of known metal cations in a data bank.
• An unknown solution is tested using dilute nitric acid solution and silver nitrate solution. What is this testing for?

  Halide ions
• Name the dilute acid that must be present in order to test for sulfate ions with barium chloride.

  hydrochloric acid
• Halide ions are tested by the precipitate when silver nitrate and nitric acid is mixed.