Topic: HCl + Na2CO3 (Read 69727 times)

Cardinnus · « **on:** March 31, 2007, 08:08:31 AM »

Hi all, I hope you guys can help me out here.

My question relates to the reaction of sodium carbonate with hydrochloric acid.
I know that Na2CO3(s) + 2HCl(aq) --> 2NaCl(aq) + H2O(l) + CO2(g)
But what about Na2CO3(aq) + 2HCl(aq)
ie. when the sodium carbonate is first dissolved in solution before adding the acid?
I have searched multiple resources but can find no conclusive answer as generally the states are not given.
Would the correct equation be: Na2CO3(aq) + 2HCl(aq) --> 2NaCl(aq) + H2O(l) + CO2(aq)
or: Na2CO3(aq) + 2HCl(aq) --> 2NaCl(aq) + H2CO3(aq)
or possibly neither of these?

I realise that the actual reaction is much more complicated than either of these equations would indicate due to the equilibriums involved with CO2(aq) and H2CO3(aq) in the above equations, but I would very much like to know the correct way to give the simple equation.
I don't mean to sound harsh but please only provide an answer if you are absolutely certain that it is correct, speculation is welcome but please ensure it is stated as such.
Any help would be very much appreciated

Cardinnus

Dan · « **Reply #1 on:** March 31, 2007, 10:17:30 AM »

Quote from: Cardinnus on March 31, 2007, 08:08:31 AM

Would the correct equation be: Na2CO3(aq) + 2HCl(aq) --> 2NaCl(aq) + H2O(l) + CO2(aq)
or: Na2CO3(aq) + 2HCl(aq) --> 2NaCl(aq) + H2CO3(aq)
or possibly neither of these?

It will actually be both, but much more of one than the other.

Have a look at this http://en.wikipedia.org/wiki/Carbonic_acid
Carbonic acid, H₂CO₃ is in equilibrium with carbon dioxide and water, but the equilibrium lies far to one side...

What will the major products be?

avjazz78 · « **Reply #2 on:** March 31, 2007, 12:38:10 PM »

Yes with Dan. Carbonic acid is one of the weakest most unstable acids there is. You can actually form it by blowing air from your mouth (ie CO2) into a cup of water. However being so unstable it quickly decomposes into H2O and CO2. So it is not going to be CO2(aq) because (at least in normal laboratory temps. and pressures) the CO2 turns to gas right away and comes out of the reaction vessel leaving you with an aqueous soln. of NaCl.

Cardinnus · « **Reply #3 on:** March 31, 2007, 07:35:46 PM »

Thanks heaps for the great replies,
From what you have said it seems the correct equation is
Na2CO3(aq) + 2HCl(aq) --> 2NaCl(aq) + H2O(l) + CO2(g)
My only question is that I have done this experiment and did not observe any bubbles in the solution, why would this be if CO2(g) is being formed?
Many thanks

Yggdrasil · « **Reply #4 on:** April 01, 2007, 08:56:21 PM »

Here's a more complete set of reactions that are happening in when you add aqueous sodium bicarbonate to aqueous hydrochloric acid:

Na₂CO_{3 (aq)} + HCl_(aq) <--> NaHCO_{3 (aq)} + NaCl_(aq)
NaHCO_{3 (aq)} + HCl_(aq) <--> H₂CO_{3 (aq)} + NaCl_(aq)
H₂CO_{3 (aq)} <--> H₂O_(l) + CO_{2 (g)}

If not enough HCl is added, then there won't be enough HCl to drive the equilibria all the way forward to favor the production of a lot of carbon dioxide, or the production of carbon dioxide will be too slow to cause bubbles to form (i.e. the gas will exchange only at the surface). If you add a large excess of HCl to aqueous sodium bicarbonate, you should see bubbles form.