MHS Chemistry
The Percentage Loss in Weight When Sodium Bicarbonate Is Decomposed by Heat

In this experiment we will analyze a sample of sodium bicarbonate to find the percentage loss in weight when it is decomposed by heat.  To do this, we will heat a known weight of sodium bicarbonate and weigh the sodium carbonate residue.


  1. Weigh a clean, dry crucible to the nearest milligram.  Add about 4 or 5 grams of sodium bicarbonate and re-weigh.  Support the crucible in a clay triangle mounted on a ring and stand.
  2. Heat the crucible in a small Bunsen flame for 2 or 3 minutes, then gradually raise the flame over a period of 5 minutes until the lower third of the crucible is dull red in color.  Turn off the burner, allow the crucible to cool, and weigh it.
  3. To make certain that the decomposition is complete, re-heat the crucible with the hottest flame of the burner for about 5 minutes.  Then allow the crucible to cool and re-weigh it.  This weight should be within a centigram or two of the weight after the first heating.  Use the smaller of the two masses in your computations.
  4. Compute (a) the weight of sodium bicarbonate used, and (b) the loss in weight.
  5. Now calculate the percentage loss in weight.
  1. Write the equation for the reaction taking place in the crucible.
  2. Calculate the percentage loss in weight from the equation.
  3. Compute your percentage error.
  4. How do you account for this error?
  5. Calculate the weight of (a) water and (b) carbon dioxide evolved during the reaction.
[Bicarbonate Decomposition score sheet][MHS Chem page]