Cations 1

• Solubility product constant is simplified equilibrium constant (Ksp) defined for equilibrium between a solids and its respective ions in a solution. Its value indicates the degree to which a compound dissociates in water.
• The higher the solubility product constant, the more soluble the compound.
• Lead chloride is one thousand times more soluble than silver chloride, and one hundred thousand times more soluble than mercurous chloride.
• Examination as to color is limited, since color is dependent upon concentration, and certain colors may neutralize each other to produce colorless solutions.
• silver chloride and mercurous chloride are almost completely precipitated
• lead chloride is always incompletely precipitated and in low concentrations may not be precipitated at all
• To get correct results in this lab, good organizational skills and techniques are essential.
• Be sure to label all tubes and solutions because these accumulate rapidly, and it is very easy to get tubes and/or solutions mixed up
• It is also suggested that students keep a “waste” beaker near their work area in which to discard all solutions locally, and then pour their combined waste solutions into the large waste container provided by the instructor at the end of lab.
• Finally, be sure to clean out and thoroughly rinse all glassware (including stirring rods!) with deionized water between uses.
• Cross-contamination is one of the most common causes for false observations leading to incorrect conclusions.
• COMPLETE PRECIPITATION = add drops until no cloudy appears
• CENTRIFUGATE/ SUPERNATANT = liquid after mixture (above)
• PRECIPITATE/ RESIDUE = solid on the bottom
• DISCARD = throw away (waste bottle)
• ACIDIFY = The pH of a solution is tested by dipping a stirring rod into the solution and then touching it to a piece of litmus paper resting on a clean, dry watch glass. If a solution is acidic it will turn blue litmus paper red. If a solution is basic it will turn red litmus paper blue.
• WASHING– add 10 drops of distilled water while stirring
• POSITIVE TEST– may be indicated by:

  1. formation of precipitate of distinct color or texture

  2. dissolution of a precipitate

  3. appearance or disappearance of a color in a solution or in a flame

  4. evolution of a gas

  5. development of a characteristic odor.
• CLEAR SOLUTION – not turbid or cloudy
• COLORLESS SOLUTION – is the one that is not colored
• The group is precipitated with dilute HCl as insoluble chlorides and the resulting precipitate washed with cold water to remove other cation group
• Lead chloride is removed from the precipitate by leaching with hot water
• The separation of AgCl from Hg2Cl2 with ammonia water
• These group of cations are insoluble when they become chlorides. They are separated from other cations when precipitated with dilute hydrochloric acid.
• Lead chloride has high solubility in water. This means that, it easily becomes soluble when dissolve in hot water. Thus heating the solution will allow the lead (II) chloride to be dissolved back in water. Thus the centrifugate contains plumbous ion
• For confirmation for Lead (II) ion use potassium chromate as precipitating agent
• To separate mercurous ion, use dilute ammonia
• dilute ammonia, to which silver is soluble and mercury forms black precipitate
• For confirmation of silver ion, the precipitating agent is nitric acid.
• Nitric Acid – acidifying to destroy the complex
• Ammonia water not only reacts with AgCl but it also serves as a medium for the auto-redox action of Hg2Cl2 to produce mercury and mercuric amino chloride, both of which are insoluble
• Metallic mercury, in a finely divided state, is black in color; therefore, a blackening at thispoint proves the presence of Hg2Cl2
• Acidifying first to dissolve the complex HgNH2Cl, Precipitating agent used should be Stannous chloride