8th Grade Home



Activity 2
Combination Reactions

Mg + O2 --->  MgO2 + H2O
magnesium + oxygen ---> magnesium oxide + water
       
Materials needed for each station:
  • 1 magnesium ribbon (2-3 cm)
  • 2 mL water in a medium test tube
  • 1 mL phenolphthalein in a small test tube
  • 1 crucible with lid
  • 1 test tube rack
  • 1 pipet (dropper)
  • 1 strip wide rang pH paper
  • 1 flame source
  • 1 ring stand or burner stand
  • 1 test tube clamp
  • 1 medium test tube
  • 1 small test tube
  • 1 medium test tube stopper

Procedures:
  1. Place 1 piece of magnesium ribbon in a crucible.  Clamp the crucible, place on the ring stand, and heat for 5 minutes.
  2. After heating for 5 minutes, add the magnesium to a test tube with 2 mL of water.  Securely  close the test tube with a rubber stopper and gently shake it.
  3. When partially dissolved in water, metal oxides (such as magnesium) produce basic hydroxides, which will show as a base when tested with pH paper.  Test the pH of the solution with a wide range pH strip.  Compare your reading to the color indicator on the pH jar.  Record the approximate pH in your lab book.
  4. Add several drops of phenolphthalein to the solution.  Phenolphthalein is an indicator solution, meaning that it can be used to determine whether a solution is a base.  When phenolphthalein is added to an acid, it produces no color change.  When phenolphthalein is added to a base, it turns pink.  Record any color change that occurs into your lab book.
  5. Answer the Results Questions for Activity 2.