Chemical Tests

• lithium burns with a red flame
• sodium burns with a yellow flame
• potassium burns with a lilac flame
• calcium burns with an orange red flame
• copper ions burn with a blue green flame
• many metal hydroxides are insoluble and precipitate out of solution when formed. add a few drops of sodium hydroxide solution of the unknown substance and find the colour of the precipitate.
• copper (II) froms a blue precipitate when sodium hydroxide is added
• iron (II) forms a green precipitate when sodium hydroxide is added
• iron (III) forms a red brown precipitate when sodium hydroxide is added
• ammonia gas has a pungent smell and turns damp red litmus paper blue
• to test for carbonates, add dilute hydrochloric acid to your sample and if carbonates are present then carbon dioxide should be released.
• carbonate + acid -> carbon dioxide + water
• to test for sulfate ions add dilute HCl followed by barium chloride solution. a white precipitate of barium sulfate means the original compound was a sulfate. the hydrochloric acid is added to remove any traces of carbonate of sulfite ions as they would produce a precipitate.
• to test for chloride, bromide or iodide ions, add dilute nitric acid followed by silver nitrate solution
• a chloride ions gives a white precipitate of silver chloride
• a bromide ion gives a cream precipitate of silver bromide
• an iodide ions gives a yellow precipitate of silver iodide
• to test for halides nitric acid is added to get rid of carbonate or sulfite ions before the test.
• why is nitric acid used in the test for halide ions and not hydrochloric acid?

  HCL would introduce Cl- ions into the sample test so would always produce a positive test for Cl-
• chlorine bleaches damp blue litmus paper white.
• oxygen relights a glowing splint.
• when carbon dioxide is bubbled through limewater, it turns the limewater cloudy.
• hydrogen extinguishes a lit splint with a squeaky pop
• ammonia turns damp red litmus paper blue and is a pungent gas.
• water turns anhydrous copper sulfate (white) to blue hydrated copper sulfate.
• when a sample is pure is has set defined physical properties like boiling and freezing point. pure water will always boil at 100C and freeze at 0C