Chemistry module 1.2

• Qualitative Analysis of Ions

  1. Testing for positive ions

  2. Testing for negative ions
• Testing for Group 2 Metal ions

  • Four test tubes should be placed in a test tube rack
  • Around 10 drops of 0.1 mol dm^-3 barium chloride solution should be added to the first test tube
  • Around 10 drops of dilute sodium hydroxide solution (NaOH) should be added to the same test tube
  • Swirl the test tube carefully to mix well
  • Continue to add sodium hydroxide dropwise to the test tube, until it is in excess
  • This should then be repeated in the other test tubes, for calcium chloride solution, magnesium chloride solution and strontium chloride solution
  • The same test as above can also be done using ammonia solution and sulfuric acid solution
• Testing for Ammonium Ions

  • About 10 drops of a solution containing ammonium ions, such as ammonium chloride, should be added to a clean test tube
  • About 10 drops of sodium hydroxide should be added using a pipette
  • The test tube should be swirled carefully to ensure that it is mixed well
  • The test tube of the solution should then be placed in a beaker of water, and the beaker of water should be placed above a Bunsen burner, so that it can become a water bath
  • As the solution is heated gently, fumes will be produced
  • A pair of tongs should be used to hold a damp piece of red litmus paper near the mouth of the test tube, to test the fumes
• Testing for Halide Ions


  • The sample being tested should be added using a pipette to a test tube
  • The test tube should be placed into a test tube rack
  • A small amount of nitric acid should be added to the sample using a pipette, followed by a small amount of silver nitrate solution
  • A precipitate will form, either white, cream or yellow, if a halide ion is present in the sample
• White precipitate


  Formed if chloride ions are present in the sample, AgCl

  
• Cream precipitate


  Formed if bromide ions are present in the sample, AgBr

  
• Yellow precipitate


  Formed if iodide ions are present in the sample, AgI
• Testing for Hydroxide Ions


  • A small amount (around 1 cm^3) of the solution should be added to a test tube using a pipette
  • Test the pH of the solution using red litmus paper or universal indicator paper

  
• Testing for Carbonate Ions


  • A small amount (around 1 cm^3) of dilute hydrochloric acid should be added to a test tube using a pipette
  • An equal amount of sodium carbonate solution should then be added to the test tube using a clean pipette
  • As soon as the sodium carbonate solution is added, a bung with a delivery tube should be attached to the test tube
  • The delivery tube should transfer the gas which is formed into a different test tube which contains a small amount of limewater (calcium hydroxide solution)
• Carbonate ions react with hydrogen ions from the acid


  Produce carbon dioxide gas
• Testing for Sulfate Ions

  • Acidify the sample with dilute hydrochloric acid and then add a few drops of aqueous barium chloride

  
• If a sulfate is present then a white precipitate of barium sulfate is formed: Ba^2+ (aq) + SO4^2- (aq) → BaSO4 (s)

  
• HCl is added first to remove any carbonates which may be present and would also produce a precipitate and interfere with the results
• Synthesis of a Haloalkane


  1. Measure 8 cm^3 of 2-methylpropan-2-ol in a measuring cylinder

  2. Pour the 2-methylpropan-2-ol into a separating funnel

  3. Using a fume hood, add 20 cm^3 of concentrated hydrochloric acid to the separating funnel in small portions of 2 - 3 cm^3 making sure to release the pressure by opening the stopper after each addition

  4. Leave the separating funnel to stand in the fume hood for 20 minutes and gently shake the separating funnel at 2 minute intervals

  5. Allow the layers to separate and dispose of the lower aqueous layer by opening the tap

  6. Add sodium hydrogen carbonate solution in small portions to the funnel and gently shake the funnel, again, release the pressure at regular intervals

  7. Pour the organic layer into a clean dry conical flask and add two spatulas of anhydrous magnesium sulfate

  8. Once clear, decant the liquid into distillation apparatus

  9. Distill the liquid and collect the distillate in the range of 47 - 53 °C
• Separating funnel


  • Allows the product to be cleaned and isolated
• Preparation of Cyclohexene


  1. Pour approximately 20 cm^3 of cyclohexanol into a round-bottomed flask

  2. Add 5 cm^3 of concentrated phosphoric acid

  3. Fit the flask with a condenser and heat the mixture gently using a water bath or heating mantle

  4. Collect the distillate in a clean, dry conical flask

  5. Wash the distillate with a saturated solution of sodium hydrogen carbonate to remove traces of acid

  6. Wash the organic layer with water to remove any remaining carbonate

  7. Add solid calcium chloride to the organic layer to remove any remaining water

  8. Decant the dried organic layer into a clean, dry distillation apparatus and distill the product, collecting the fraction boiling at 82-84 °C
• Elimination mechanism for cyclohexanol

  The mechanism for the reaction is shown, but you do not need to know this, and you could be asked in a question to draw in the relevant charges or lone pairs
• Preparation of Cyclohexene


  1. Pour cyclohexanol into flask

  2. Slowly add phosphoric acid

  3. Add anti-bumping granules

  4. Heat flask gently

  5. Collect distillate
• Purification of Cyclohexene


  1. Pour distillate into separating funnel

  2. Add sodium hydrogen carbonate solution

  3. Separate layers

  4. Add anhydrous calcium chloride

  5. Transfer liquid to clean, dry beaker

  
• Bromine water test confirms cyclohexene as an alkene (colour change from orange brown to colourless)
• Oxidation of Ethanol


  1. Add acidified potassium dichromate(VI) solution to flask

  2. Cool flask in ice bath

  3. Set up reflux apparatus

  4. Add ethanol dropwise

  5. Heat for 20 minutes
• Ethanol is flammable, so electric heater or water bath must be used instead of naked flames
• Purification of Oxidation Products


  Distill the reaction mixture
• Hydration of Hex-1-ene


  1. Prepare ice bath

  2. Add hex-1-ene to boiling tube

  3. Slowly add concentrated sulfuric acid

  4. Add distilled water

  5. Separate layers

  6. Dry hexan-2-ol with sodium carbonate

  7. Filter

  8. Distill to collect hexan-2-ol fraction
• Hexan-2-ol


  • Higher boiling point than hex-1-ene due to hydrogen bonding
  • Formed as the more stable secondary carbocation intermediate
• Tests on hex-1-ene and hexan-2-ol

  • Bromine water test
  • Acidified KMnO4 test
  • Sodium metal test
  • Combustion test
• The mechanism for hydration of hex-1-ene involves formation of a secondary carbocation intermediate