My guess is what is being observed is that initially, the silver begins dissolving in the nitric, but the reaction begins to slow rapidly - silver is not very soluble in concentrated (say 70%) nitric acid. This is because the solution is already heavy with ions.
The addition of distilled water gives the silver nitrate somewhere to dissolve after reaction with the acid (silver nitrate 219gm / 100ml solubility in H2O). So, the addition of distilled water would give the false appearance that it is making the reaction proceed, when really, it is allowing the silver to be more easily dissolved into solution.
First of all apologies if i caused offence that was not my intention.
Secondly if this comes a cross as condescending that is also not my intent.
You are correct in that solids will stop dissolving in liquids when they reach a certain concentration. So if this was just a dissolving reaction the above would be true. ( this is called the saturation point of a liquid) Try dissolving table salt in water. Eventually it will stop dissolving.
However the above is a chemical reaction. So the more concentrated the solution the quicker it would proceed (rate kinetics).
If you look at the equation:
Ag + 2HNO3 --> AgNO3 + NO2 + H2O
For every four ions you lose (the 2HNO3 on the left of the reaction) you only gain 2 ions (AgNO3) so the actual concentration of ions decreases. This is in direct opposition to the implied part of the statement "This is because the solution is already heavy with ions". In this case the "dissolving" of the silver is not related to the concentration of ions in solution.
I have made one assumption. I am assuming that they have added enough volume of acid to dissolve all the silver present.
hope this helps.
Nick
The addition of distilled water gives the silver nitrate somewhere to dissolve after reaction with the acid (silver nitrate 219gm / 100ml solubility in H2O). So, the addition of distilled water would give the false appearance that it is making the reaction proceed, when really, it is allowing the silver to be more easily dissolved into solution.
First of all apologies if i caused offence that was not my intention.
Secondly if this comes a cross as condescending that is also not my intent.
You are correct in that solids will stop dissolving in liquids when they reach a certain concentration. So if this was just a dissolving reaction the above would be true. ( this is called the saturation point of a liquid) Try dissolving table salt in water. Eventually it will stop dissolving.
However the above is a chemical reaction. So the more concentrated the solution the quicker it would proceed (rate kinetics).
If you look at the equation:
Ag + 2HNO3 --> AgNO3 + NO2 + H2O
For every four ions you lose (the 2HNO3 on the left of the reaction) you only gain 2 ions (AgNO3) so the actual concentration of ions decreases. This is in direct opposition to the implied part of the statement "This is because the solution is already heavy with ions". In this case the "dissolving" of the silver is not related to the concentration of ions in solution.
I have made one assumption. I am assuming that they have added enough volume of acid to dissolve all the silver present.
hope this helps.
Nick
