Chemical tests

• To test for hydrogen:

  • Use a burning splint held at the open end of a test tube of the gas
  • creates a squeaky pop if present
• To test for Hydrogen:

  • Use a burning splint held at the open end of a test tube of the gas
  • creates a squeaky pop sound if present
• To test for oxygen:

  • Uses a glowing splint inserted into a test tube of the gas
  • splint relights in oxygen
• To test for Carbon Dioxide:

  • Bubble the gas through the limewater (calcium hydroxide) and it will turn milky (cloudy)
• To test for ammonia:

  • Makes damp red litmus paper turn blue
  • Forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it
• To test for chlorine:

  • when damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
• To carry out a flame test to test the presence of Alkali metals:

  • take a sample of the metal on a wire and put it in a flame, the flame will turn a specific colour, showing what metal it is
• Lithium (Li+) Red
• Sodium (Na+) yellow
• Potassium (K+) lilac
• Calcium (Ca2+) orange-red
• Copper (Cu2+) blue-green
• Describe tests for these cations: NH4+ using NaOH (aq) and identifying the gas evolved, Cu2+, Fe2+ and Fe3+ using NaOH (aq)

  • Ammonia reacts with NaOH (aq) forming NH3 (g), use damp red litmus paper - it will turn blue showing the presence of ammonia gas
  • Copper (II) produces a blue precipitate
  • Iron (II) produces a green precipitate
  • Iron (III) produces a brown precipitate
• Describe how to test for HNO3(aq): Add dilute sulfuric acid (H2SO4) and heat gently. The colour changes from clear to white as bubbles are produced. This indicates that NO2(g) has been formed. Then add excess KMnO4(aq) and boil. The MnO2(s) turns black but when excess KMnO4(aq) is added, the black MnO2(s) dissolves leaving a pale pink/purple solution which confirms the presence of NO3-(aq)
• To test for halide ions:

  • first add dilute nitric acid, followed by silver nitrate solution
  • chloride gives a white precipitate
  • bromide gives a creamy precipitate
  • Iodine gives a yellow precipitate
• To test for sulfate ions:

  • First, add dilute hydrochloric acid, followed by barium chloride solution
  • white precipitate will form when sulfate ions are in this solution
• To test for carbonate ions:

  • Carbonates react with dilute acids to create carbon dioxide
  • This gas can be bubbled through limewater if the limewater goes cloudy , the gas is CO2
• Anhydrous copper (II) sulfate is a white solid that is insoluble in water

  • when water is present, it turns blue