Qualitative analysis

• Qualitative analysis is a process used to identify substances that contain ions in solution, a type of compound, and atoms.
• To identify the unknown ions In a solution, reagents are added.
• NH4OH(aq) aqueous Ammonium Hydroxide and NaOH(aq) aqueous Sodium Hydroxide are the reagents used to identify or test for cations. 
• Ca2+, Al3+, Pb2+, and Zn2+ are all cations that form white precipitates when NaOH(aq) is added.
• Fe2+ Iron(ii) hydroxide forms a green Precipitate when NaOH is added. When excess NaOH is added the precipitate remains the same and it is insoluble.
• Fe3+ iron(iii) hydroxide forms a red-brown Precipitate when NaOH(aq) is added. When excess NaOH(aq)is added the precipitate remains the same and it is insoluble.
• NH+ 4 ammonium is the only cation in which when NaOH(aq) is added a precipitate is not formed but ammonia gas is emitted on warming. This changes moistened red litmus paper to blue.
• Calcium hydroxide, copper (ii) hydroxide iron (ii) hydroxide, and iron (iii) hydroxide are basic hydroxides so they do not react with sodium hydroxide. When excess NaOH (aq) is added to these precipitates they remain.
• Metals from basic hydroxides.
• Aluminum hydroxide, lead (ii) hydroxide, and zinc hydroxide amphoteric hydroxide. They react with excess NaOH (aq) to form soluble salts, therefore the precipitates formed dissolve.
• Ammonium hydroxide is soluble therefore no precipitate is formed when NaOH (aq) is added.
• A white precipitate is formed when NaOH (aq) is added to Ca2+. The precipitate remains the same when excess NaOH (aq) is added and it is insoluble.
• A white precipitate is formed when NaOH (aq) is added to Al3+. The precipitate dissolves and forms a colorless solution when excess NaOH (aq) is added and it is soluble.
• A white precipitate is formed when NaOH (aq) is added to Pb2+. The precipitate dissolves and forms a colorless solution when excess NaOH (aq) is added and it is soluble.
• A white precipitate is formed when NaOH (aq) is added to Zn2+. The precipitate dissolves and forms a colorless solution when excess NaOH (aq) is added and it is soluble.
• A blue precipitate is formed when NaOH (aq) is added to Cu2+. The precipitate remains when excess NaOH (aq) is added and it is insoluble.
• Out of Ca2+, Al3+, Pb2+, and Zn2+; Ca2+ is the only one that when excess NaOH (aq) is added is insoluble and the precipitate remains white, the others dissolve and form a colourless solution and are soluble.
• A blue precipitate is formed when NaOH (aq) is added to Cu2+. The precipitate remains when excess NaOH (aq) is added and it is insoluble. 
• A green precipitate is formed when NaOH (aq) is added to Fe2+. The precipitate remains when excess NaOH (aq) is added and it is insoluble. 
• A red-brown precipitate is formed when NaOH (aq) is added to Fe3+. The precipitate remains when excess NaOH (aq) is added and it is insoluble. 
• The metal cations except Ca2+ form an insoluble metal hydroxides when ammonium hydroxide solution is added.
• Al3+, Pb2+, and Zn2+ are all cations that form white precipitates when NH4OH(aq) is added.
• A white precipitate is formed when NH4OH (aq) is added to Al3+. The precipitate remains the same when excess NaOH (aq) is added and it is insoluble. 
• A white precipitate is formed when NH4OH (aq) is added to Pb2+. The precipitate remains the same when excess NaOH (aq) is added and it is insoluble. 
• A white precipitate is formed when NH4OH (aq) is added to Zn2+. The precipitate dissolves and forms a colorless solution when excess NH4OH (aq) is added and it is soluble. 
• Out of Al3+, Pb2+, and Zn2+; Zn2+ is the only one that when excess NH4OH (aq) is added, the precipitate dissolves and form a colourless solution and is soluble while the others remain white precipitates and insoluble.
• A blue precipitate is formed when NH4OH (aq) is added to Cu2+. The precipitate dissolves and forms a dark blue solution when excess NH4OH (aq) is added and it is soluble. 
• A green precipitate is formed when NH4OH (aq) is added to Fe2+. The precipitate remains when excess NaOH (aq) is added and it is insoluble. 
• A red-brown precipitate is formed when NH4OH (aq) is added to Fe3+. The precipitate remains when excess NaOH (aq) is added and it is insoluble. 
• Aluminum hydroxide, lead(ii) hydroxide iron(ii) hydroxide, and iron(iii) hydroxide do not react with NH3 (aq). When excess NH3 (aq) is added these precipitates remain the same.
• Zinc hydroxide and copper(ii) hydroxide do react with NH4OH (aq). They react with the excess NH4OH (aq) forming complex soluble salts, therefore the precipitates dissolve.
• Al3+ and Pb2+ ions are the only cations that cannot be distinguished. To be able to distinguish between them, add Potassium iodide solution. Al3+ forms no precipitate while Pb2+ forms a bright yellow precipitate.
• To test for anions in gas, it is heated.
• CO2 gas is given off when CO3 2- carbonate is heated and a white precipitate forms in lime water.
• Oxygen gas is given off when Potassium nitrate KNO3 or Sodium Nitrate NaNo3 is heated and the glowing splint relights.
• Nitrogen dioxide and oxygen are the gases given off when calcium nitrate is heated and a brown gas is seen and the glowing splints relight.
• To identify some nitrates NO2 - add concentrated sulfuric acid and a few drops of copper turnings into a sample and heat it. A blue solution is formed and a brown nitrogen dioxide gas is emitted.
• To test for some carbonates and sulphates ions, dilute hydrochloric or nitric acid is added, and test the gas given off. It can be heated if necessary.
• When dilute acids are added to carbonates a white precipitate is formed in lime water and carbon dioxide is emitted.
• Sulfur dioxide is emitted when dilute acids are added to sulphates. Acidified potassium manganate (vii) solution changes from purple to colourless.