(2) The burning of red phosphorus consumes oxygen. When the spring clip is opened, the water in the beaker enters the gas container, accounting for about one-fifth of the volume of the gas container, so it can be proved that oxygen accounts for about15 of the total air volume;
(3) From the experimental phenomenon in (2), it can be concluded that oxygen accounts for about one-fifth of the air volume;
(4) Nitrogen does not burn or support combustion, and is insoluble in water;
(5) The problems that should be paid attention to in the experimental operation are: good air tightness of the device; Red phosphorus should be enough; Cool to room temperature before opening the spring clip.
Answer:
( 1)4P？ Light it? . ? 2P2O5
(2) Water enters the gas cylinder, accounting for about 15 of the remaining volume of the gas cylinder.
(3) Oxygen accounts for about one fifth of the air volume;
(4) Do not burn or support burning, and are insoluble in water.
(5) The air tightness of the device is good.