Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Bel-p on April 02, 2006, 06:51:38 PM
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This is something I really don't understand, and I'm not even sure how to ask the question - but I'll try. Why isn't water part of the reaction in reactions between solutions?
EG:
sodium hydroxide (aq) reacts with hydrochloric acid (aq) to make sodium chloride and water.
NaOH + HCl --> NaCl + H20
As both of the reactants contain water, why doesn't the first part of the equation contain H2O? And how do I know that the H2O that is apparently produced in the reaction isn't just the H2O that was in the two reactants in the firsts place?
Am I making any sense at all? This question has been baffling me since I started (Sept 05).
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If your looking for a really simple reason then...
Think of the water that the HCl and NaOH are in as being only a medium that the reaction takes place in. It's only holds the 2 compounds and the subsequent reaction.
If your looking for a more specific reason with more chemistry terms, then you'll just have to hope one of the many professional chemists here will respond to your question.
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You can represent water as a subscript (aq) to show that the species is dissolved in water.
NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l)
You know this is the water molecule produced in this reaction simply because that is why you have written the reaction, to show the reaction between hydroxide and hydrogen ions:
OH- + H+ ---> H2O
If you did this experimentally you would have a hard time showing which molecule was produced from the reaction and which was already in teh bulk solution. You could possibly use deuterium (although I am not sure how exactly).
Water does not appear on the reactant side of the equation because it is a product of the reaction. It just also happens to be the medium the reaction is done in.
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This is something I really don't understand, and I'm not even sure how to ask the question - but I'll try. Why isn't water part of the reaction in reactions between solutions?
EG:
sodium hydroxide (aq) reacts with hydrochloric acid (aq) to make sodium chloride and water.
NaOH + HCl --> NaCl + H20
As both of the reactants contain water, why doesn't the first part of the equation contain H2O? And how do I know that the H2O that is apparently produced in the reaction isn't just the H2O that was in the two reactants in the firsts place?
Am I making any sense at all? This question has been baffling me since I started (Sept 05).
Don't mind the quote, did this to refresh memory.
This is my own theory which I thought about it :P
Firslty, NaOH in water
NAOH --> NA+(aq) + OH- (aq)
Not forgetting the equilibrium in water( H2O molecules ), there would be more OH- than H+ in water, making the solution alkaline. Same goes to HCL in water, which makes the solution acidic.
Mixing both of them only gives you
Na+(aq), CL-(aq), and H2O!?!? WHat happen to the H+ and OH-?
Simple, the only reaction taking place is only H+ and Oh-.( This can be confirm using standard enthapy of neutralisaion) Due to the abundance in the 2 solution, they reacted together to form H2O molecules maintaing the equlibrium in water.
Some may wonder why does only the H+ and OH- react? My only possible guess is the strong electrostatic attraction between these 2 molecules wheras NA+ and Cl- are still strongly bonded to H2O molecules via ion dipole attraction.
Note in some neutralisation, a SOLID salt( For eg silver chloride) is produced? Why? The direct and foremost reason is Kip salt > Ksp. However what does they explain? Someone might want to answer me that ;D My only guess is the energy involed using some formula