Help with the effect of Sodium Hydroxide and Germinating Seeds.

Bob Vickery vickery at MPX.COM.AU
Sat Nov 16 01:12:50 EST 1996


Paul Koch wrote:
>I have been investigating seed's cellular resperation by doing a lab that
>required putting germinating seeds in the bottom of a test tube.  Then a
>layer of cotton was put on top of that.  On top of this, I put a thin
>layer of Sodium Hydroxide and then another layer of cotton.  I put this
>test tube upside down in a beaker of water and let it sit over night.  The
>next day I found that the amount of air in the test tube had greatly
>decreased.  I also found that the layer of Sodium Hydroxide had
>disappeared.  I know that a germinating seed takes in oxygen to preform
>areobic resperation and as a byproduct of this, Carbon Dioxide is
>produced.  But, where did the carbon dioxide go and where did the sodium
>hydroxide go?  Why didn't the carbon dioxide take up the same amount of
>space as the air the seed took in?  I would appreciate it if you could
>answer these questions and maybe go further in depth into these processes.

Your seeds should have produced a volume of carbon dioxide equal in volume
to the oxygen consumed, or maybe a bit more.  The carbon dioxide must have
disappeared, partly by reacting with the sodium hydroxide to make sodium
carbonate, and partly by dissolving in the water (carbon dioxide is more
soluble in water than oxygen is).  The sodium hydroxide and sodium
carbonate absorb water vapour and become liquid so they probably drained
out of your tube.  Soda lime is more convenient for this experiment since
it doesn't turn to liquid.
There are a number of assumptions in my explanation.  You could test them
experimentally.
Cheers

Bob Vickery
bob at acsusun.acsu.unsw.edu.au
vickery at mpx.com.au





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