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Experiment 13 - Thermal Decomposition of Sodium Bicarbonate
NaHCO3 (s) is commonly called sodium bicarbonate. When NaHCO3 is heated
above 110 oC (but not heated to "red heat") it has been observed that both H2O (g) and
CO2 (g) are evolved by some chemical change, and that after this decomposition is
complete, a white solid residue remains. Among possible reactions, the two following
unbalanced reactions seem the ones that are most likely to explain these facts:
NaHCO3 (s) à Na2CO3 (s) + H2O (g) + CO2 (g) (reaction A)
sodium bicarbonate sodium carbonate water vapor carbon dioxide
NaHCO3 (s) à Na2O (s) + H2O (g) + CO2 (g) (reaction B)
sodium oxide
You are to choose between reactions (A) and (B) on the basis of your laboratory
work, which will involve heating a weighed sample of sodium bicarbonate in a crucible
and weighing the residue left in your crucible after heating. From the mass of the solid
product ("residue"), you should be able to decide if the product of the reaction is Na2O (s)
or Na2CO3 (s).
Safety Precautions:
• Wear your safety goggles.
• Use care when handling HCl (aq). If any HCl splashes on your skin or clothes, rinse it
off immediately with plenty of water.
Waste Disposal:
• The solid waste may be discarded in one of the regular garbage cans.
Procedure
1. Obtain a clean, dry crucible that has no cracks.
