Teaching High School Chemistry
  • Introduction
  • Book
  • Blog
  • Topic List
  • Teaching Resources
  • Biography
  • Contact

Decomposition of sodium bicarbonate

1/14/2014

0 Comments

 
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. 

Picture
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!








0 Comments



Leave a Reply.

    Author

    Marjorie R. Heesemann is a chemistry teacher with 15 years of experience who is now working to develop resources for the Chemistry classroom.

    Archives

    February 2019
    January 2019
    December 2018
    November 2018
    October 2018
    September 2018
    August 2018
    July 2018
    June 2018
    May 2018
    April 2018
    March 2018
    February 2018
    January 2018
    December 2017
    November 2017
    October 2017
    September 2017
    August 2017
    July 2017
    June 2017
    May 2017
    April 2017
    March 2017
    February 2017
    January 2017
    December 2016
    November 2016
    October 2016
    September 2016
    August 2016
    July 2016
    June 2016
    May 2016
    April 2016
    March 2016
    February 2016
    January 2016
    December 2015
    November 2015
    October 2015
    September 2015
    August 2015
    July 2015
    June 2015
    May 2015
    April 2015
    March 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    July 2014
    June 2014
    May 2014
    April 2014
    March 2014
    February 2014
    January 2014

    Categories

    All

    RSS Feed

Powered by Create your own unique website with customizable templates.