A gas jar was inverted over burning yellow phosphorus floating over water in a beaker. After burning, the water level was found to rise in the gas…

Question

A gas jar was inverted over burning yellow phosphorus floating over water in a beaker. After burning, the water level was found to rise in the gas jar. The water level rises because

Answer 1

A gas jar was inverted over burning yellow phosphorus floating over water in a beaker. After burning, the water level was found to rise in the gas jar. The water level rises because

pressure inside the gas jar is greater than pressure outside it
the air in the gas jar had been used up by burning
oxygen in the gas jar had been used up by burning ✓
nitrogen in the gas jar had been used up by burning

Explanation

Yellow (white) phosphorus burns in oxygen to form solid phosphorus (V) oxide: 4P + 5O₂ → P₄O₁₀. The solid takes up almost no space, and it dissolves in the water.

So the oxygen in the jar is removed, and the gas pressure inside falls below the pressure outside. Water is pushed up into the jar to take its place. It rises by about one-fifth, the share of oxygen in air.

It is not all the air that is used up. Nitrogen and the other gases stay in the jar.

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