JAMB Chemistry 1978 Question 46

Question 46

Air

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

  1. A.pressure inside the gas jar is greater than pressure outside it
  2. B.the air in the gas jar had been used up by burning
  3. C.oxygen in the gas jar had been used up by burning
  4. D.nitrogen in the gas jar had been used up by burning
  5. E.the temperature in the jar had risen considerably.
Show the answer and explanation

Answer: C (oxygen in the gas jar had been used up by burning)

Explanation

Phosphorus burns using up the oxygen (about one-fifth of the air) and the oxide dissolves; water rises to take its place. Nitrogen is not used.