Prep of Silver Nitrate AgNO3

[jmarjorie]

Dear All,

 

What would be the best method of preparing silver nitrate AgNO3 using Nitric acid HNO3. Would like the EXACT quantitative proportions of metallic Silver & Molarity of HNO3.

The solution got was highly acidic (pH 1) even though no more silver reacted.

Is heat necessary ? Is there a catalyst to speed up the reaction ?

No text book gives this.Thanks in advance,

jmarjorie

chemicals555@yahoo.com

[insane_alien]

1 word - equilibrium.

 

changing the temperature will shift it. i can't remember the enthalpy values off the top of my head but if its endothermic raise the temp. if its exothermic lower the temperature.

 

or maybe the salt is acidic, or the solution is saturated. if its the former then the HNO3 is used up, if the latter try adding more water.

 

Do you not need aqua regia to dissolve silver or is it reactive enough for nitric acid to do the job(I can't remember)

[woelen]

This is NOT an equilibrium reaction. You simply need to add silver metal to excess HNO3. Using the precise stoichiometric amounts does not work, you need quite some excess HNO3.

Heating the mix certainly helps, but even then, an excess amount of HNO3 is needed.

Fortunately, AgNO3 crystallizes very well and heating of the AgNO3/HNO3 mix certainly gives you nice and dry crystals of AgNO3. If you want really pure (non-acidic) AgNO3, then you need to add the crystals of AgNO3 to a small amount of distilled water and then heat to dryness again. This will drive off virtually all HNO3, which was trapped in the crystals in the first batch.

 

With "heating to dryness" I mean careful heating. First heating, such that a wet slurry appears, with some white solid and then letting all remaining liquid evaporate on a hot room-heater, by letting it stand undisturbed for a day or so. Put a thin paper tissue above the liquid, in order to avoid all kinds of dust entering the liquid while it is drying.

 

A word of warning: AgNO3 really stains your skin and it destroys most organic matter, itself becoming black. Once, you have dry powder/crystals, store it in a small well-stoppered glass bottle.

[YT2095]

Hmmm... now that`s interesting!

I store mine as saturated liquid with excess Silver in the bottom of a "Blacked out" bottle.

the excess nitric idea though???? is that just for crystalisation purposes only?

[insane_alien]

oops sorry wasn't quite awake then

[woelen]

Hmmm... now that`s interesting!

I store mine as saturated liquid with excess Silver in the bottom of a "Blacked out" bottle.

the excess nitric idea though???? is that just for crystalisation purposes only?

No, it is not for crystallisation purposes, but you need excess acid in order to dissolve all silver.

 

The oxidizing power of nitrate ion strongly depends on the pH of the solution. Look at the Nernst equation of the oxidizing power of nitrate as function of pH and concentration. Then you'll see that its oxidizing power almost has gone in aqueous solution for any pH well above 0. Only at appreciable concentration and sufficiently low pH, nitrate ion in aqueous solution is a strong oxidizer. So, below a certain concentration, its oxidizing power simply is not enough anymore to dissolve silver metal.