Identification of ions by chemical and spectroscopic means

• Flame tests can be used to identify metal ions.
• Aluminium, calcium and magnesium ions form a white precipitate with NaOH.
• Only aluminium’s precipitate dissolves when excess NaOH is added.
• Copper(II) produces a blue precipitate.
• Iron(II) produces a green precipitate.
• Iron(III) produces a brown precipitate.
• Cu 2+ + 2OH- -> Cu(OH)2.
• The number of OH- ions needed is equal to the charge on the metal ion.
• The Na from the NaOH and whatever the metal ion was bonded to will react to form a compound together.
• 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.
• Halides can be identified using a method involving dilute nitric acid and silver nitrate solution.
• Chloride gives a white precipitate.
• Bromide gives a cream precipitate.
• Iodide gives a yellow precipitate.
• Sulfates can be identified using a method involving dilute hydrochloric acid and barium chloride solution.
• A white precipitate will form when sulfate ions are in this solution.
• Elements and compounds can be detected and identified using instrumental methods.
• These methods are accurate, sensitive and rapid, making them advantageous compared to chemical tests.
• Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions.
• The sample is put into a flame and the light given out is passed through a spectroscope.
• The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.