very simple question (1 Viewer)

[*mememe*]

hi
i was just looking through conquering chemistry p. 144 and i dont under stand why does it have two different equations:
-it says when hydrogen carbonate is placed in acidic soloution it produces carbonic acid (conjugate acid)

however near the bottom it says hydrogen carbonate is placed in acidic soloution producing water and carbon dioxide (in chemical equation ofcourse which im unable to use in this thread --no experience)

anyways could some1 plz help me cos im a bit confused as to which one u would write in the exams

thx cheers

 

[za]

its the same thing.
the 3rd eqtn on the page shows that carbonic acid forms water and carbon dioxide.
so in the 2nd eqtn u replace the H2CO3 with the water and CO2.

 

[*mememe*]

so which one would u use in exams?

 

[BlackJack]

I'm not clear on what you're asking...

H2CO3 exists in several forms in (and out of) solution. it goes like this:
H2O + CO2(gas) <-> H2CO3 <-> H⁺ + HCO3^- <-> 2H⁺ + CO3^2-

What you get when you place hydrogen carbonate in an acidic solution depends one how acidic the soluton is. the amount of carbon dioxide that comes out depends on the acidity, though for the things you'll be dealing with will always result in at least some CO2.
The carbonate is itself a buffer and will take/remove H+ ions according to equilibirum. I gues that the first equation tells you this: it says that you put in hydrogen carbonate (HCO3) in acidic solution. HCO3 + H+ <-> H2CO3. This is a buffer reaction, and you obtain carbonic acid. Then the 2rd eq. goes on to say that carbonic acid dissociates and turns into CO2.
You should probably state both in an exam, since the formation of carbonic acid will lead (to varying degrees) to the formation of carbon dioxide.

 

[*mememe*]

thats very helpful
thx