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Questions 4.1a

  1. Write the procedure for this experiment. -----------------------------------------
  2. What is the function of sodium hydroxide solution? ---------------------------
  3. Describe what happens when the gas jar is inverted to cover the burning candle. -------------------------------------------------------------------
  4. The height AB of the gas jar was initially occupied by air. How can we proceed to find out the percentage of air that was used up in the burning of the candle? ---
  5. In one such experiment, AB was 20 cm and the height finally occupied by air was 16 cm. Use this information to determine the percentage of air that takes part in burning (active air). ----------------------------------------------------------------------------
  6. What is the name of the active gas in air? --------------------------------------------
  7. The products of this reaction are water and carbon (IV) oxide. Representing the candle as Wax, write a word equation to show the burning of the candle in air. ---


Answers to Questions 4.1a

  1. Place a bee-hive shelf at the bottom of the trough, then half-fill the trough with water. Invert a gas jar to rest on the shelf. Tie a rubber band around the gas jar to mark the level of water. Remove the gas jar and place a short burning candle to float on water. Invert the gas jar over the candle and let its mouth rest on the bee-hive shelf. Wait till the candle goes off and water level stops rising. Measure the height by which water level rises and the total length AB and use them to calculate the percentage of active air.
  2. To absorb carbon (IV) oxide gas produced during burning of the candle
  3. The candle continues to burn briefly then goes off. Water rises in the jar upto a certain level and stops.
  4. We note the amount of space the water rises to cover. This equals the volume of air used in burning. The ratio of this volume to AB is the fraction of air used up.
  5. Percentage of air used = (20-16/20)/100 = 20%
  6. Oxygen
  7. Wax + Oxygen Water + Carbon (IV) oxide