Ch 22 - (Chemical analysis)
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What are anions?
Negatively charged non - metal ions are known as anions
What are the major tests for anions?
• Carbonate ions (CO32-) • Halide ions (Cl-, Br-, I-) • Sulfate ions (SO42-) • Sulfite ions (SO32-)
What is the ion for carbonate?
CO32-
What is the test for carbonate ion?
• add dilute acid • bubble the gas through limewater • limewater turns cloudy if carbonate ion is present
What should the observation be for a positive test for carbonate ion?
• fizzing \ effervescence • CO2 is produced • White precipitate of calcium carbonate
What is the chemical equation for the test of carbonate ions?
CO32- (aq) + 2H+ (aq) —> CO2 (g) + H2O (l) CO2 (g) + Ca(OH)2 (aq) –> CaCO3 (s) + H2O (l) White precipitate limewater turns cloudy
What are halide ions?
• negative ions • anions formed by elements in Group 7
What is the test for halide ions?
• acidify the sample with nitric acid • add silver nitrate solution, AgNO3 • silver halide precipitate
What is the word and symbol equation for the reaction between potassium chloride and silver nitrate?
Word: Potassium chloride + silver nitrate –> potassium nitrate + silver chloride Symbol: KCl (aq) + AgNO3 –> KNO3 (aq) + AgCl (s)
What is the observation for the reaction between potassium chloride and silver nitrate?
chloride ions form white precipitate
What is the word and symbol equation for the reaction between potassium bromide and silver nitrate?
Word: Potassium bromide + silver nitrate –> potassium nitrate + silver bromide Symbol: KBr (ag) + AgNO3 (aq) –> KNO3 (aq) + AgI (s)
What is the observation for the reaction between potassium bromide and silver nitrate?
bromide ion forms a cream precipitate of silver bromide
What is the word and symbol equation for the reaction between potassium iodide and silver nitrate?
Word: Potassium iodide + silver nitrate –> potassium nitrate + Silver iodide Symbol: KI (aq) + AgNo3 (aq) –> KNO3 (aq) + AgI (s)
What is the observation for the reaction between potassium iodide and silver nitrate?
Iodide ions form a yellow precipitate of silver iodide
What is the ion for sulfate?
SO42-
What is the test for sulfate ion?
• acidify the sample with dilute hydrochloric acid • add a few drops of barium chloride solution
What is the symbol equation for reaction of barium reacting with sulfate?
Ba 2+ (aq) + SO42- (aq) –> BaSO4 (s)
What is the ion for sulfite?
SO3 2-
What is the test for sulfite ion?
• add dilute acid • warm the mixture gently • bubble the gas released through potassium manganate (VII) solution • potassium manganate (VII) solution changes from purple to colorless if sulfate ion is present.
What is an ammonium ion?
NH 4+
What is the test for ammonium ions?
• gently warming a solution with the ions and sodium hydroxide solution • source of hydroxide solution OH- • releases ammonia gas which turns damp red litmus paper • cations in aqueous solution can be identified by colour of precipitate they form • Transition metals produce hydroxides with distinctive colours
What happens if ammonia solution and metal hydroxide are added togteher?
It form a metal hydroxide precipitate
What happens if excess ammonia solution is added to metal hydroxides?
• some precipitate may re-dissolve • that’s why few drops are very slowly dropped
How do u test metal ion with ammonia?
• add a few drops of ammonia solution • record any color changes or precipitates formed • add excess ammonia solution • record any color changes to precipitates