What will be the action of dil nitrarous acid and dil nitric acid solution separately on acidified potassium iodide solution and why?


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This message has been edited. Last edited by: DorianGreyed,

If I understand we have a solution of HN02 and KI and a 2nd solution of HN03 and KI.
What happens in each case?
This sounds like an application to use an EMF table and half reaction potentials.

From Lange's Handbook of chemistry the Reduction potentials are
HN02 + H+ e- = NO + H20 +0.98V
HN03 +3H+ 2e- = HN02 + H20 +.94 V
I2(aq) + 2e- = 2 I- +.621 V


Both the nitrous and nitric reactions have a stronger reduction potential. The Iodide should give up an electron and form Iodine in solution. In adition N0 is formed.
Depending upon your initial concentrations. The solution should turn brown both due to the Iodine and N0. If the concentrations are high enough the NO may bubble off into the air and react with oxygen forming poisonous brown N02.

The potassium should stay in solution.

I added KI solution to dilute solution of nitric acid and to the mixture of sodium nitrite + dil HCl separately. Solution turned brown in case of the latter only. I request Mr Peteeo to confirm it by experiment and inform us the result, if I go wrong.

A probable Explanation:

Being a strong acid nitric acid ionizes completely in dil solution and nitrate ions produced in solution are highly solvated by water molecules thus the +ve charge on the central atom is partially neutralized by the negative charge on the water dipole. This phenomenon makes the hydrated nitrate ions less susceptible to be reduced by iodide ions in solution.
Being weaker than nitric acid nitrous acid remains in solution mostly in unionized state and that is why central nitrogen atom in the molecule is more susceptible to reduction by iodide ion than hydrated nitrate ions.

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Please inform me if anything wrong with this explanation, I like to learn the right explanation.

Sorry.. I'm between jobs at the present and do not have a lab to work from.

you are now more of an expert as you've done the reactions.

Nitric acid is a strong acid. HN02 has a pKa of 3.3 and would be in equilibrium.
The rate of reaction may be influenced as you suggest due to the concentration of the various Ions but not preventing the reaction from occuring.

I'll need to do some further study.

Eagerly waiting to know the result of further study from Mr. Peteeo.