# Chemical Concentration question



## kane333 (Mar 29, 2013)

Hi all, I tried searching the term with no results. I was looking through HNO3 and H2SO4 MSDS to verify page 54 of Hokes that states H2SO4 takes longer to cool than HNO3 due to the higher boiling point for H2SO4. While doing a search on the web for prices and where HNO3 can be purchased, I found that the local Grainger sells the acid but they use a different term for the chemical concentration. 

http://www.grainger.com/Grainger/LABCHEM-Nitric-Acid-9APM5?Pid=search

2.0N & 6.0N are the chemical concentrations shown. Does anyone know the percent value of these numbers?


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## solar_plasma (Mar 29, 2013)

Yes.



> http://en.wikipedia.org/wiki/Molar_concentration



...it's mol/l
1 mol = the number of atomic weight * gramm

H = 1,00..
O = 16,..

H2O = 1+1+16=18

1 mol H2O = 18 g

calculate the mol weight for your acids, multiplicate them with the offered concentrations in mol (example: 2M or 2N), then you get how many gramm acid there is on 1 l liquid.Then divide with 10 and you have c in wt%.


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## FrugalRefiner (Mar 29, 2013)

kane333 said:


> Hi all, I tried searching the term with no results. I was looking through HNO3 and H2SO4 MSDS to verify page 54 of Hokes that states H2SO4 takes longer to cool than HNO3 due to the higher boiling point for H2SO4.


If both acids were heated to the same temperature, they would cool at _close_ to the same rate. But because sulfuric acid boils at a much higher temperature than nitric, it would take sulfuric a longer time to cool from a boil than nitric.



> While doing a search on the web for prices and where HNO3 can be purchased, I found that the local Grainger sells the acid but they use a different term for the chemical concentration.
> 
> 2.0N & 6.0N are the chemical concentrations shown. Does anyone know the percent value of these numbers?


Concentrated nitric acid (68 to 70%) is about 15.8N / 15.8M. When we dilute nitric acid 50/50 with water, we create about 7.9N acid. The 6N could work for some processes. The 2N is likely to dilute.

That's some pretty pricey acid. I would keep looking.

Hope that helps,
Dave


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## mikeinkaty (Apr 1, 2013)

FrugalRefiner said:


> 2.0N & 6.0N are the chemical concentrations shown. Does anyone know the percent value of these numbers?


Concentrated nitric acid (68 to 70%) is about 15.8N / 15.8M. When we dilute nitric acid 50/50 with water, we create about 7.9N acid. The 6N could work for some processes. The 2N is likely to dilute.

Dave[/quote]

Dave - I used to think that using a 50/50 solution to dissolve sterling was simply to slow down the reaction. But something I read inferred that the 50/50 mix was necessary to get the proper reaction and should be done at ambient temperature. Is this true and if so, why? Just curious. I've never tried anything other than a 50/50 mix. Even at 50/50 the reaction can boil over if one does not have sufficient headroom in the vessel.

Mike


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## FrugalRefiner (Apr 1, 2013)

Mike,

I'm not a chemist, so I may not be able to explain it in a technically accurate way. When you dissolve something in a solvent, chemical bonds in the substance to be dissolved have to be broken to form ions, and the bonds of the solvent are disrupted to hold the ions in solution. 

Every substance has a solubility limit - only so much of it can be dissolved in a given amount of the solvent. So if you put a little sugar in some water, it dissolves. If you keep adding sugar, you'll reach a point where no more will dissolve and the excess will simply drop to the bottom. But if you add more water, more sugar will dissolve.

HNO3 is more soluble in water than AgNO3. At 20°C. (68°F.), a liter of water can hold about 2,200 grams of AgNO3. The molecular weight of AgNO3 is 169.874 grams per mole. Dividing 2,200 grams by 169.874 shows us that about 12.95 moles of AgNO3 can dissolve in 1 liter of water.

Concentrated nitric acid (68 - 70%) is about 15.8 molar, meaning there are 15.8 moles of HNO3 dissolved in each liter of acid. Note that is 15.8 moles of HNO3 per _liter of acid_, not per _liter of water_. Concentrated nitric acid has a density of about 1.42, so 1 liter of acid weighs about 1,420 grams. We know that there are 15.8 moles of HNO3 in that weight. Each mole of HNO3 weighs 68.012 grams, so 15.8 moles times 68.012 grams per mole means we have 1,074.59 grams of HNO3 in that liter of acid. That leaves about 345 grams of water (1,420 grams per liter of acid - 1,074.59 grams of HNO3) in the liter of acid. Since the density of water is 1.00, we find we only have about 345 ml. of water in each liter of concentrated acid.

So if we try to dissolve our silver into concentrated HNO3, we can only get about 4.47 moles of silver to dissolve in the 345 ml. of water in each liter of acid, leaving excess, unused HNO3 still in the solution. Diluting the acid with water provides a greater volume of water into which the silver can dissolve. A 50/50 mix of 1 liter of concentrated HNO3 and 1 liter of water will give us 1.345 liters of water containing 15.8 moles of HNO3. 1.345 liters of water can hold 17.42 moles of AgNO3. The 50/50 ratio allows us to completely consume the HNO3 with a little excess water left.

I know that's a long explanation, but you did ask. :lol: I hope it makes sense.

Adding your acid in small increments will help to avoid those boil overs, but you are right in using a vessel with plenty of extra room as well.

Dave


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## mikeinkaty (Apr 1, 2013)

Thanks dave - That makes perfect sense. I guess you could say the water is the 'carrier' and without it there is not enough room for the silver.

I first put in half the calculated amount of nitric then when that has slowed down put in 1/4 the recommended amount. By then the silver has been pretty well digested when covering the vessel with a watch glass. After that last reaction has stopped I throw in some silver to see what happens. I also put the vessel inside a plastic container. Learned that the hard way. Well, I knew to do that but got sloppy.

Mike


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