Required Practical 7

Aim

Using chemical tests to identify the ions in unknown single ionic compounds covering the ions from topics 8.3.1 to 8.3.5

Materials Needed

• Unknown samples of the following single ionic compounds: lithium, sodium, potassium, calcium, copper, aluminium, magnesium, iron (II), iron (III), halide, and sulfate.
• Test tubes or small containers for each unknown sample.
• Droppers or pipettes for adding reagents.
• Test tube rack.
• Distilled water.
• Specific chemical reagents for each ion - for example, you can use:
  • Sodium hydroxide solution (NaOH)
  • Hydrochloric acid (HCl)
  • Ammonia solution (NH₃)
  • Silver nitrate solution (AgNO₃)
  • Barium chloride solution (BaCl₂)
  • Potassium chromate solution (K₂CrO₄)
  • Potassium permanganate solution (KMnO₄)
  • Potassium dichromate solution (K₂Cr₂O₇)
  • Potassium thiocyanate solution (KSCN)

Safety Precautions

• Wear safety goggles and a lab coat to protect against accidental splashes.
• Do not ingest or touch any chemicals or solutions, and handle all materials with care.

Procedure

1. Label each test tube or container with the name of the unknown ion.
2. Add a small amount of the unknown sample to each test tube.
3. Perform specific chemical tests for each ion as follows:
   1. For alkali metal ions (lithium, sodium, potassium): Add a few drops of sodium hydroxide solution (NaOH). Observe for the formation of a coloured precipitate.
   2. For alkaline earth metal ions (calcium): Add a few drops of hydrochloric acid (HCl). Observe for effervescence (bubbles of gas) due to the release of carbon dioxide.
   3. For copper (II) ions: Add a few drops of ammonia solution (NH₃). Observe for the formation of a deep blue precipitate.
   4. For aluminium ions: Add a few drops of sodium hydroxide solution (NaOH). Observe for the formation of a white gelatinous precipitate that dissolves in excess NaOH.
   5. For magnesium ions: Add a few drops of sodium hydroxide solution (NaOH). Observe for the formation of a white precipitate.
   6. For iron (II) ions: Add a few drops of potassium chromate solution (K₂CrO₄). Observe for the formation of a green precipitate.
   7. For iron (III) ions: Add a few drops of potassium thiocyanate solution (KSCN). Observe for the formation of a deep red colour.
   8. For halide ions (chloride, bromide, iodide): Add a few drops of silver nitrate solution (AgNO₃). Observe for the formation of coloured precipitates (silver chloride - white, silver bromide - cream, silver iodide - yellow).
   9. For sulfate ions: Add a few drops of barium chloride solution (BaCl₂). Observe for the formation of a white precipitate.
4. Conclusion:
   1. Record the observations for each test and compare them to known results for each ion.
   2. Identify the ions present in each unknown single ionic compound based on the observed reactions.
   3. Reflect on any potential sources of error and suggest improvements for future experiments.