Chemical tests

• hydrogen (H2)

  Use a lit splint

  Gas pops
• oxygen (O2)

  Use a glowing splint

  Glowing splint relights
• carbon dioxide (CO2)

  Bubble the gas through limewater

  Limewater turns cloudy
• ammonia (NH3)

  Use red litmus paper

  Turns damp red litmus paper blue
• chlorine (Cl2)

  Use damp litmus paper

  Turns damp litmus paper white (bleaches)
• A flame test is used to show the presence of certain metal ions (cations) in a compound.

  • A platinum or nichrome wire is dipped into concentrated hydrochloric acid to remove any impurities.
  • The wire is dipped into the salt being tested so some salt sticks to the end.
  • The wire and salt are held in a non-luminous (roaring) bunsen burner flame.
  • The colour is observed.
• lithium (Li⁺)

  red
• sodium (Na⁺)

  yellow
• potassium (K⁺)

  lilac
• calcium (Ca²⁺)

  orange-red
• copper (II) (Cu²⁺)

  blue-green
• Add sodium hydroxide and warm, and if ammonium ions are present, ammonia gas will form, turning red litmus blue
• Copper (II) turns blue when added to sodium hydroxide
• Iron (II) turns dark green when added to sodium hydroxide
• Iron (III) turns red/brown when added to sodium hydroxide
• Cl- gives a white precipitate of silver chloride when added to silver nitrate
• Br- gives a cream precipitate of silver bromide when added to silver nitrate
• I- gives a yellow precipitate of silver iodide when added to silver nitrate
• To test for a sulphate ion, add dilute HCl then barium chloride solution, which produces a white precipitate
• To test for carbonates, add dilute HCl, and test for any carbon dioxide produced by running it through limewater
• To test for water, add anhydrous copper sulphate to the sample and if water is present it will turn blue
• If a water sample is pure, it will boil at 100$^{\circ}$C and freeze at 0$^{\circ}$