# 65% Nitric acid



## Dude4ever (Apr 12, 2012)

Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
This is really the highest (and only) concentration I can buy, if I don't want to buy 25L minimum of nitric though, and I really don't


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## goldsilverpro (Apr 12, 2012)

Dude4ever said:


> Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
> This is really the highest (and only) concentration I can buy, if I don't want to buy 25L minimum of nitric though, and I really don't


Sure. You could use 50%. I always liked a little splash of water in my aqua regia, anyway.


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## maynman1751 (Apr 12, 2012)

> I always liked a little splash of water in my aqua regia, anyway.



I like mine on the rocks, neat! :mrgreen:


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## Dude4ever (Apr 13, 2012)

Okey, wow, the recipe I got from Samuel's website calls for concentrations between 69-72%, and he does not mention diluting it, that is why I ask


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## goldsilverpro (Apr 13, 2012)

65% is fine


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## bobgaz (May 16, 2012)

Hi 
I am
In Massachusetts (western) and cannot find a supplier of Nitric Acid anywhere. 
Are you able to get yours as you stated at a pharmacy chain and if so which one?
I am trying to save and get it as local as I can .... Shipping is a killer!
Thanks


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## Geo (May 16, 2012)

Dude4ever lives in Norway, thats a long way from Mass.

sourcing nitric acid is a big problem here in the U.S. because it is so dangerous.


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## Harold_V (May 17, 2012)

goldsilverpro said:


> I always liked a little splash of water in my aqua regia, anyway.


Yep! I did, too. 

Harold


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## butcher (May 17, 2012)

If you are heating a metal in Aqua Regia the water will assist in keeping the acids in solution reacting with your metals instead of evaporating off in gasses, so I also will use a little water in my reactions, especially if heating the solution for long periods of time as the solutions also will loose water in the process and concentrate the acids as the solution evaporates while dissolving the metals in solution.


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## gsfnbc (May 22, 2012)

bobgaz said:


> Hi
> I am
> In Massachusetts (western) and cannot find a supplier of Nitric Acid anywhere.
> Are you able to get yours as you stated at a pharmacy chain and if so which one?
> ...



Have you tried your local Grainger store? They might have it.


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## Geo (May 22, 2012)

:lol: :lol: http://www.grainger.com/Grainger/LABCHEM-CHEM-GOLD-CHLRD-1PCT-WV-125ML-8G299?Pid=search

i wish i could get that much for it.


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## goldenye (Jun 25, 2012)

what is the least concentrated nitric that can be used in AR?
i use 15% nitric (Ph modifier at garden center) to dissolve cheap jewelery.

is it good enough for AR?


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## lazersteve (Jun 25, 2012)

Your nitric acid will be fine for AR, but you will need to adjust the amount used to dissolve the gold. The normal recipie is 4ml:1ml; 31% HCl: 70% Nitric Acid per gram of gold to be dissolved. 

Your nitric is 15% :

70%/15% = 4.67

So you will need roughly 4.67 mL of 15% nitric acid to 4 ml of 31% HCl per gram of gold to be dissolved. I rounded up so you could easily get by with 4.5mL:4mL of your nitric to hardware store muriatic acid.

Steve


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## goldsilverpro (Jun 26, 2012)

Mathematically, using the specific gravities of 70% and 15% nitric, at 20C, I came up with a ratio of 6.08 to 1, in strength. Therefore, if you want to end up with a comparable ratio of 4 to 1, 32% HCl/70% HNO3, you would use a ratio of about 6ml of 15% HNO3 and 4ml of 32% HCl. If anyone wants to know the math on this, let me know.

When you do this, however, you end up with very close to 50/50 aqua regia, due to all the extra water in the 15% nitric. It would be like making up a 4/1, 32% HCl/70% HNO3, AR, and then adding an equal volume of water. 

This would work fine (but, slower) in most cases, such as in dissolving gold foils or the gold powder left from inquartation. A guy I knew used a 50/50 diluted aqua regia to dissolve all gold ceramic CPU packages, in about 50 pound lots. I'm thinking he heated it somewhat but am not sure about that. He used the dilute AR because it cut down on the fumes and eliminated boilovers. It worked fairly well but it took about 3 days and, even then, I don't think he got all the gold braze under the silicon chip. If he had had the patience (and the money) to leave it for a few more days, he might have gotten it all. He then dropped the gold with SO2. All of the gold dropped but it was only about 97% pure.

About the only other item I can see any problems with would be if you were trying to directly dissolve karat gold jewelry. It might still work but it would certainly be much slower.


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## lazersteve (Jun 26, 2012)

Chris,

I'm not quite understanding how you derived your answer.

Here's was my thinking:

It would require 2x the amount of 35% HNO3 as 70% HNO3;
or 4x the amount of 17.5% HNO3,
or 6x the amount of 8.75% HNO3.

From the chart you posted here the density slope is nearly linear at STP.

Nitric Acid Specific Gravity Chart

15% HNO3 has a sp gr of approximately 1.09 g/cc
70% HNO3 has a sp of approximately 1.42 g/cc

Steve


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## goldsilverpro (Jun 26, 2012)

I used this S.G. chart. On the link you gave, I think the guy made the graph from this chart.
http://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry

According to this chart:

At 20C, the S.G. of 15% nitric = 1.0842g/ml. Therefore, 1 ml would contain 1.0842 X .15 = .1626g HNO3
At 20C, the S.G. of 70% nitric = 1.4134g/ml. Therefore, 1 ml would contain 1.4134 X .70 = .9894g HNO3

Therefore, the strength ratio is .9894/.1626 = 6.08

Using similar logic, when you dilute 1 ml of 70% nitric with 1 ml of water, you end up with 2 ml of 41% nitric. Here's the math:

1 ml of 70% nitric weighs 1.4134g and contains 1.4134 X .70 = .9894g of HNO3. 1 ml of water weighs 1g (or close enough to not really affect the results). Added together, the 2 ml weighs 2.4134g. The percentage by weight of HNO3 is .9894/2.4134 = .41 or 41%

I know it doesn't seem to make much sense. Before I did the math, I thought the same as you did - that 50/50 70% nitric was 35% by weight. The problems are that these weight percentages aren't exactly linear and that weight percentages and volume percentages are like apples and oranges. I have come to the conclusion that, if you want accuracy in these type calculations, you MUST use the S.G. charts. I started the thread that you gave the link for. Check the first post on the first page of the thread. Better still, re-read the whole thread.


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## lazersteve (Jun 26, 2012)

I was formulating another reply to your previous post and while running the numbers the light went off about the percentage being non-linear as well. 

I did the math and it worked out to ~40% for 50/50 also by my numbers. 

All this time I was assuming 50/50 was 35% also.

Steve


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## Harold_V (Jun 26, 2012)

lazersteve said:


> It would require 2x the amount of 35% HNO3 as 70% HNO3;


That isn't true because you're not dealing with 100% with the 70% solution. The ratios do not remain as a constant. 

It works the same way as discounts. Buy something with a 40% discount isn't the same as buying with a 30% discount, then an additional 10% discount. Get my drift?

Harold


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## jeneje (Jun 26, 2012)

gsfnbc said:


> bobgaz said:
> 
> 
> > Hi
> ...


Don't know if this will help you but try Greenwaychemical.com
Ken


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## butcher (Jun 27, 2012)

If using the dilute nitric to dissolve gold, silver or another metal, I would consider several options.

Add HCl, then add the dilute nitric acid in increments, as the solution concentrated the water in solution would evaporate off, (in the reaction the water evaporates first, then nitric then HCl, they do not come off in vapors pure , but mostly these solutions as gases in that order), as long as you do not heat too strongly the acids would attack the metals, dissolving them as salts in solution, as the acids concentrate the metals would react more, (also the water in solution can help keep the nitric from going off in Nox gas before reacting with the metal as solution concentrates as long as you did not have the heat too high, it would take a little longer because you would be diluting the solution some with each addition of the dilute nitric acid, you would also have to not let the heat reacting on this solution get too high, because it would take a little while to remove the water and as the nitric solution concentrated the acid would begin to react much more vigorously (if the temperature was too high at this stage you would have a boil-over, as the nitric would be beginning to react seemingly all at once), (this same thing can happen when using more concentrated acids).

Silver could also be dissolved in the dilute nitric acid using heat to drive off water, as in the reaction described above.

Or you can concentrate your dilute nitric acid, (then use it as concentrated 68%, or just concentrate it up to what percentage you wish to use like approximately 40% or silver), using heat to drive off water until the azeotope of 68% nitric acid was reached, paying attention to the temperature of the reaction and controlling the temperature can be used in this process, (nitric acid has differing boiling points depending on concentration of the acid).


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## goldsilverpro (Jun 27, 2012)

I agree with butcher. No matter what I was dissolving, I would cover the material with HCl, heat it, and then add the 15% nitric in increments until the material is dissolved. I never pre-mix aqua regia.


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## AndyWilliams (Nov 21, 2012)

Long dead thread, but just the answer I needed. I finally found some nitric, 42%. Paid $17.50/gallon, no idea if that's good or not, but glad to have some in my hands!


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## butcher (Nov 21, 2012)

AndyWilliams,

That will be about the correct strength for silver or copper.
The 42 % HNO3 will be very close to using 70% HNO3 and diluting with water 50%-50%.
I would figure about 2.8ml of this to each gram of silver.
For 70% nitric use about 1.4ml nitric and 1.4ml water for each gram of silver.
The 42% HNO3 figure about 8.3ml per gram of copper.
For 70% HNO3 4.3 ml HNO3 and 4.3ml of water.
I will normally use a little more water or hydrogen peroxide with heating to keep fumes down, and keep the nitric in solution to react more with metals.


For Aqua regia to dissolve gold free of base metals 3.8 ml 32%HCl + 0.95ml 70% HNO3 per gram of gold, nitric acid is measured out in clean container and added in portions with a pipette, using heat after initial reaction, and heating to evaporate and drive off H2O, when I still have some gold undissolved gold left I will evaporate and concentrate the solution from a yellow solution to a red solution this will use up more nitric already in solution and dissolve more gold in the process, after solution is evaporated down to the burgundy red color, I will add a few drops of nitric at a time {adding splash of HCl just in case I am limited on HCL, and evaporating off the little water involved here with this added acid, as the HCl is about 68% H2O). Once concentrated the added drops of nitric finish dissolving the last bit of gold, this eliminates my need to spend long hours evaporating off free nitric acid, or from having to add pure gold to use up excess HNO3 in solution, I feel it is the best use of both GSP's trick of limiting HNO3, and Harold's trick of adding gold to eliminate free nitric acid, with this method I can then dilute solution (if I think I had a little nitric left in solution I will add a pinch of sulfamic acid, if done right this is not needed), and let it settle over night to precipitate any silver chloride before filtering into very clean vessel and precipitating the gold. 
(Another option to insure not over using nitric is to leave a bit of undissolved gold to process with the next batch).

The formula I use above came from Hokes book and works very well, 4 floz 32% HCL and 1 floz 70% HNO3 for each troy ounce of gold.
Which is about 118ml HCL and 29.5ml HNO3 per troy ounce of gold.
Which is about 8 tablespoons HCl and 2 tablespoons HNO3 to dissolve a troy ounce of gold.
As you see here it takes very little acid to dissolve a lot of gold.


Your 42% HNO3 is more dilute with water, but you can use it just fine in the reaction described above to dissolve gold, you will have to about double the nitric volume measure, and you will also have to account for the excess water in the acid when concentrating the solution, or figure the excess water your adding (in the acid as you add more acid to the concentrated solution which will dilute it a little and the added water will need re-concentrated), but you will also have less nitric acid wasted as gas in the reaction if done right.

Edited to correct mistake in figures


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## mikeinkaty (Dec 8, 2012)

Dude4ever said:


> Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
> This is really the highest (and only) concentration I can buy, if I don't want to buy 25L minimum of nitric though, and I really don't


What pharmacy did you buy it from? The rest of us would like to know!


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## jimdoc (Dec 8, 2012)

mikeinkaty said:


> Dude4ever said:
> 
> 
> > Does 65% technical grade nitric acid, bought from pharmacy cut it in making AR?
> ...




Dude4ever is in Norway, and has not been on the forum since Wed Jun 13, 2012.

Jim


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## AndyWilliams (Dec 8, 2012)

butcher said:


> AndyWilliams,
> 
> That will be about the correct strength for silver or copper.
> The 42 % HNO3 will be very close to using 70% HNO3 and diluting with water 50%-50%.
> ...




Thanks for the info butcher, it's much appreciated. I remember Hoke writing that most beginners use too much acid, now I can see why. It is easy to see that much money can be saved in these stages if I'm careful. My question though, wouldn't I need to use 5.6 ml of 42% nitric to dissolve a gram of silver and 16.6 ml per gram of copper?

Thanks again!

Andy


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## butcher (Dec 8, 2012)

Andy

It looks like I goofed up those numbers I will edit them
Please see edited correction above in color


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## AndyWilliams (Dec 8, 2012)

butcher said:


> Andy
> 
> It looks like I goofed up those numbers I will edit them
> Please see edited correction above in color



Wow! Even less acid! Thanks butcher!


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## butcher (Dec 9, 2012)

Andy,
Depending how the reaction is driven, or run (dilution, refluxing, temperature, and other factors play a big role in how much acidis needed and how much is lost in gases evolved from the reaction), you may get by with even less than these figures, it really is amazing to me how little aqua regia it takes to dissolve gold, and how much gold can be in a concentrated gold chloride solution after de-noxing the solution and concentrating the solution (driving off most of the free acids).


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