When water is placed in a balloon, the balloon can be placed over a flame without popping. Water absorbs the heat from the flame, so the rubber of the balloon does not become weak and break like it does with the dry balloon.
Hot water expands so it is less dense than room temperature water. Cold water contracts so it is more dense than room temperature water. The red hot water rises and the blue cold water sinks.
When different ionic compounds are heated, electrons around the metal atom become excited and jump energy levels. When the electrons fall back to ground state they release light and heat energy. The amount of energy released determined the wavelength and color of the light released, resulting in different colored flames.
When a small amount of water is heated inside the can, steam is produced, filling the can. When the can is inverted into cold water, all of the steam condenses quickly causing the can to implode.