A decomposition reaction can easily be performed by heating sodium hydrogen carbonate (aka sodium bicarbonate or baking soda):
2 NaHCO3 --> Na2CO3 + H2O + CO2
The carbon dioxide and water leave the system as a gas. I have performed this reaction in a crucible in a clay-triangle on a ring-stand and over a Bunsen burner, but I lost a lot of product with the rapid release of the gases. I could actually see the stream of white powder leaving the system when performing this lab.
2 NaHCO3 --> Na2CO3 + H2O + CO2
The carbon dioxide and water leave the system as a gas. I have performed this reaction in a crucible in a clay-triangle on a ring-stand and over a Bunsen burner, but I lost a lot of product with the rapid release of the gases. I could actually see the stream of white powder leaving the system when performing this lab.
I never tried to use a cooler setting on the Bunsen burner by closing off some of the air vents. This would result in a flame that is more yellow than blue. If you end up trying this, write and let me know!I started performing this lab by heating the crucibles in an laboratory oven.
Remember that the crucible gets very hot! I've had a few students touch the crucible, flinch and knock over the entire setup. Be careful! Remind students to detect the heat with the back of their hand, and to use their crucible tongs!
The results can be very good and lead to some good values to work with stoichiometrically.
The Theoretical Yield can be calculated based on the mass of sodium hydrogen carbonate:
# grams NaHCO3 x 1 mol NaHCO3/84 g NaHCO3 = # mol NaHCO3
# mol NaHCO3 x 1 mol Na2CO3 / 2 mol NaHCO3 = # mol Na2CO3
# mol Na2CO3 x 106 g Na2CO3 / 1 mol Na2CO3 = # gramsNa2CO3
I separated these 3 calculations to aid students in focusing on what is happening and not get lost in the calculations. Of course, these 3 calculations can be put together:
# grams NaHCO3 x 1 mol NaHCO3/84 g NaHCO3 x 1 mol Na2CO3 / 2 mol NaHCO3 x 106 g Na2CO3 / 1 mol Na2CO3 = # gramsNa2CO3
Then the lab measurements can be used to calculate an Actual Yield.
These values can then be used to calculate a Percent Error.
(experimental value) − (true value)
% error = ――――――――――――― × 100
true value
The absolute value is typically reported (negative symbols are not included).
Here is one lab procedure you could use:
http://phs.princetonk12.org/teachers/FOV2-0001F947/AccelChem/Labs/A19Lab-DecompBakeSoda.pdf
Please write if you have any questions or comments!
Remember that the crucible gets very hot! I've had a few students touch the crucible, flinch and knock over the entire setup. Be careful! Remind students to detect the heat with the back of their hand, and to use their crucible tongs!
The results can be very good and lead to some good values to work with stoichiometrically.
The Theoretical Yield can be calculated based on the mass of sodium hydrogen carbonate:
# grams NaHCO3 x 1 mol NaHCO3/84 g NaHCO3 = # mol NaHCO3
# mol NaHCO3 x 1 mol Na2CO3 / 2 mol NaHCO3 = # mol Na2CO3
# mol Na2CO3 x 106 g Na2CO3 / 1 mol Na2CO3 = # gramsNa2CO3
I separated these 3 calculations to aid students in focusing on what is happening and not get lost in the calculations. Of course, these 3 calculations can be put together:
# grams NaHCO3 x 1 mol NaHCO3/84 g NaHCO3 x 1 mol Na2CO3 / 2 mol NaHCO3 x 106 g Na2CO3 / 1 mol Na2CO3 = # gramsNa2CO3
Then the lab measurements can be used to calculate an Actual Yield.
These values can then be used to calculate a Percent Error.
(experimental value) − (true value)
% error = ――――――――――――― × 100
true value
The absolute value is typically reported (negative symbols are not included).
Here is one lab procedure you could use:
http://phs.princetonk12.org/teachers/FOV2-0001F947/AccelChem/Labs/A19Lab-DecompBakeSoda.pdf
Please write if you have any questions or comments!
RSS Feed