Observations and results
Did the sodium chloride–coated tip burn pure yellow-orange and the copper sulfate burn bluish-green?
A typical flame will burn yellow-orange with a little bit of blue near the base of the wick. When you burned the skewer tip coated with sodium chloride, you should have seen that the flame was pure yellow-orange (without any blue). This is because when the metal sodium is burned, it makes intense yellow-orange light. When you burned the skewer tip coated with copper sulfate, you should have seen that the flame gained blue-green traces. This is because when the metal copper is burned, it makes bluish-green light.
If an atom's electrons lose energy, they drop down to a lower energy level, and the lost energy can be released as light. Different types of atoms, or elements, have different gaps between their energy levels, which causes them to make light of different colors when they're burned and lose that energy.
Be sure to extinguish the candle and the skewers when you are done with the activity. When you are sure they have been extinguished (after dipping them in the water container), you can dispose of the used skewers in the garbage.
More to explore
Flame Tests, from University of California, Davis, ChemWiki
Flame Tests: Flame Coloration by Element, from Mineral News
Fun, Science Activities for You and Your Family, from Science Buddies
Rainbow Fire, from Science Buddies