tests

• gases: chlorine

  1. Use a drop of tap water to dampen a piece of blue litmus paper 
  2. Hold the paper near to a sample of chlorine water and observe what happens to the litmus paper 
  3. If chlorine is present, the litmus paper will turn red. 
  4. This reaction (chlorine + water) produces bleach, which will turn the litmus paper white. 
• gases: oxygen

  1. Oxygen gas can be made by decomposing hydrogen peroxide with manganese IV oxide. 
  2. Collect 15cm3 of hydrogen peroxide in a small conical flask or test tube. 
  3. Add a small amount of manganese oxide using a spatula. 
  4. Light a splint then blow it out so that it is glowing and insert into the test tube or concal flask. 

  If the gas is oxygen, the splint will relight.
• gases: hydrogen

  1. Place a 2cm strip of magnesium metal in a test tube and cover with 5cm3 of hydrochloric acid.  
  2. Place the palm of your hand over the test tube and gently shake for 1 minute 
  3. Then place a lit splint over the mouth of the tube after removing your hand.  
  4. If there is hydrogen present, then you will hear a squeaky pop.  
• gases: carbon dioxide

  1. Half-fill a test tube with limewater and place it in a test tube rack. 
  2. Put the end of the delivery tube into the limewater 
  3. Add about 25cm3 of hydrochloric acid to a conical flask and add a few marble chips.  
  4. Quickly put a bung on the conical flask and observe the limewater. 
  5. If carbon dioxide is present, the limewater in the test tube will turn cloudy because this reaction produces a white calcium carbonate precipitate.  
• halides

  To test for chloride ions, bromide ions and iodide ions, add some

  • dilute nitric acid followed by a few drops of silver nitrate solution:
  • chloride: white precipitate [silver chloride]
  • bromide: cream precipitate [silver bromide]
  • iodide: yellow precipitate [silver iodide]
• chloride - white precipitate
• bromide - cream precipitate
• iodide - yellow precipitate
• carbonate ions

  1. First add some barium chloride solution
  2. If there are carbonate ions present, this will produce a white precipitate of barium carbonate. 
  3. Then add some dilute hydrochloric acid
  4. If there are carbonate ions present, the mixture will fizz [because it produces carbon dioxide gas. 
  5. If you collect the gas and conduct the limewater test, the limewater should turn cloudy [to prove that it is carbon dioxide]. 
• sulfate ions

  1. First add some barium chloride solution
  2. If there are sulfate ions in the solution, a white precipitate of barium sulfate will form. 
  3. Then add some dilute hydrochloric acid. 
  4. Barium sulfate will NOT react with hydrochloric acid, so the white precipitate will NOT DISSOLVE. 

  → this is how you tell the difference between sulfate ions and carbonate ions. 
• Flame Test:

  • You can test for various metal ions by putting your substance in a flame and seeing what colour the flame goes. 
  • This only works if the unknown compound contains just one type of metal ions → or you will get a confusing mixture of colours
• flame test

  1. First clean the nichrome wire loop by dipping it into hydrochloric acid and then rinsing in deionised water. 
  2. Then drip the wire loop into a sample of the metal compound and put the loop in the clear BLUE part of the flame. 
  3. Record what colour the flame goes. 
• flame test - colours

  lithium - crimson red

  calcium - brick red

  potassium - lilac

  sodium - yello

  copper - blue green
• sodium hydroxide test

  • Many metal hydroxides are insoluble and precipitate out of solution when formed. Some of these hydroxides have a characteristic colour

  1. Add a few drops of sodium hydroxide solution to a solution of your mystery compounds. 
  2. If a hydroxide precipitate forms, you can use its colour to tell which metal ion was in the compound. 
• sodium hydroxide test colours

  iron (II) - green

  iron (III) - brown

  copper - blue

  calcium - white

  zinc - white at first, then a colourless solution