ZIMSEC O Level Combined Science Notes: Experiment: Investigating the gas produced by acids and carbonates

Aim: To investigate the reaction of acids and carbonates and the gas that is produced

Materials: sodium corbonate/sodium hydrogen carbonate (baking soda), dilute hydrochloric acid/vinegar, lime water/ligted splint, 2 test tubes

Acids and carbonates react to release carbon dioxide

Acids and carbonates react to release carbon dioxide


  1. Half fill one of the test tubes with lime water
  2. Put a small amount of the carbonate into a second test tube
  3. Pour some acid/vinegar over the carbonate
  4. Put a cork/thumb over the test tube to trap the gas that is produced
  5. Remove your thumb/cork and “pour” the gas into the second test tube (with lime water)
  6. Place a thumb over the test tube with limewater and shake it.
  7. Alternatively you might try insterting a lighted splint into the first test tube quickly after removing your thumb or the cork

Observation and results

  • There is fizzing/effervescence and bubbles forming when the acid is added to the carbonate
  • The gas builds up and its pressure can be felt on the thumb
  • The sound of gas escaping can be heard when the cork/thumb is removed
  • The gas produced turns lime water milky
  • It also extinguishes a lighted splint when it’s inserted in the first test tube


  • Acids react with carbonates to produces carbon dioxide
  • \text{carbonate+acid}\rightarrow\text{salt+water+carbon dioxide}

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