EXPLAIN THE OBSERVATIONS FROM THE FOLLOWING PROCEDURE
REACTION OF MAGNESIUM OXIDE AND AN INDICATOR.
Piece of magnesium ribbon, tongs, burner, watch glass, deionised water, solutions of phenolphthalein and 1.0M hydrochloric acid in dropper bottles.
- Using tongs, hold a piece of magnesium ribbon 2 - 3 centimetres long in a hot flame until it ignites. (DO NOT LOOK DIRECTLY AT BURNING MAGNESIUM: the brightness of the flame can damage the eyes.)
- Place the white ash from the burnt magnesium in a watch glass and add about a millilitre of water to the ash.
- Add ONE DROP of phenolphthalein to the moistened ash, and observe any changes that develop.
- Add ONE DROP of 1.0M hydrochloric acid solution to the mixture, rock the watch-glass gently to help mixing, then let the watch glass stand. Observe any changes that occur.
- After the mixture has stood for a few minutes, step d may be repeated.
OBSERVATIONS AND INTERPRETATIONS
Four observations should be recorded and explained.
- What is the apparent solubility in water of the white ash from the burnt magnesium? What is the name of the substance forming the ash?
- What is the effect of adding phenolphthalein to the moistened ash? What does this observation suggest about the ash?
- What is the immediate effect of addition of a drop of hydrochloric acid? How can this immediate effect be explained?
- What further change is observed when the mixture is allowed to stand for several minutes? How can this second change be explained?