ACID QUESTION

I'm no chemist, but my work with precious metals got me somewhat acquainted with acids. One of the things you get when you buy the higher concentrations isn't just that, you also pay for the level of purity. Reagent grade nitric acid was guaranteed to have fewer contaminants, for which you paid more money. A lot more money. I'm sure that, depending on the methods employed to manufacture the acids, high levels of quality were also obtained by tech grades, but there was no guarantee. I can only assume that it would be much like buying bar stock for the shop. If you want a guarantee of quality, you buy certified material, for which you pay slightly more, if not a lot more.

Perhaps someone in the chemical industry will clarify this for all of us.

Harold

No.

White fuming nitric acid contains more than 97.5% , less than 2% water, and less than 0.5% of oxides of nitrogen. It should be colorless or pale yellow. It is decomposed by sunlight or elevated temperatures which should suggest why you can't make it by boiling off water.

Red fuming nitric acid contains more than 86% nitric acid, 6-15% oxides of nitrogen, and less than 5% water.

Open bottles of chemicals are usually of unknown composition and not worth saving. Be careful with this stuff as it has a fast and vicious bite.

Doing a Google search for fuming nitric acid on

I got:

100% pure, anhydrous nitric acid is a colourless anhydrous solid. What we call 'concentrated nitric acid' is actually a solution of 68% by weight HNO3 in water (16M), and is often pale yellow as a result of photochemical decomposition which gives NO2. By dissolving even more NO2 into the pure material produces red 'fuming' nitric acid, which is an extremely powerful acid and oxidising agent using in the semiconductor industry for cleaning silicon wafers.

Titration will give you the percentage, but specific gravity is the easy way.

Paul K. Dickman

Measuring the specific gravity with a hydrometer might get you close. Titrating - neutralizing a specific amount of the unknown strength acid against a known concentration of a base, using an indicator such as phenolpthalein solution to determine when you hit neutral, measuring the exact amount of base needed and then doing the calculations - will give you an exact number.

Many solutions have what is called an azeotropic point, or constant boiling mixture. When you boil them, either the acid or the water will come off faster until that point is reached. I couldn't find it in my chemical handbook (it should be there) and can't remember where it is for nitric acid, but believe it is well below the fuming or the 70 percent levels.

Hope this helps.

John Martin

Not true. Purity and concentration are independent variables. Both lab grades and technical grades are available in a variety of concentrations. Lab grades cost more than technical grades; higher concentrations cost more than lower concentrations; and smaller quantities cost more (on a $/volume basis) than larger quantities, sometimes much more.

For example, VWR offers 0.5 L of reagent grade HNO3 for $49.35 (70%) and $184.55 (90%). The 70% is also offered in a 2.5 L container for $67.65, which is less than $20 more than the cost of the 0.5 L container, or nearly a 73% discount! Go figure. VWR doesn't list any technical grade HNO3.

Finding a source for small quantities of technical grade HNO3, especially in the higher concentrations, can be problematic. If you know of a good source, please share!

Bert

Sorry to say my information reflects my experiences of days long gone. I sold my refining business in '94, in no small part because of the terrible increases in the price of acids and more restrictions placed on me because of my location, which was not exactly suited to the activities at hand. However, I was buying tech grade HNO3 from Great Western Chemical for just over $200 per drum, which I owned, a lucky purchase from the UofU surplus store. As you know, the drums are stainless and have a tremendously expensive deposit ($400 at that time) if you don't happen to own your own. I went through a drum (50 gallons as I recall) about twice a year.

The only purchases of reagent grade nitric I made were in 5 pint bottle case lots, and they were higher in concentration, and correspondingly higher in price, too. It was for that reason I assumed that quality went hand in hand with concentration, but I realize that there could be a need for high purity at lower concentrations, so what you had to say makes sense. I used reagent grade for my testing solutions, so my demand was relatively small.

You think HNO3 is expensive? Try pricing bromine! I used that as an oxidizer for gold recovery from complex ores using cyanide. Killer expensive in small quantities, yet completely affordable if bought in volume. At least it was that way back then (about 1980).

Oh, yeah. While I could have stayed in business, I chose to retire early. Operating costs didn't really drive me away. Love being retired!

Harold

From the American Chemical Society Specifications Reagent Chemicals Eighth Edition

Assay....69.0-71.0% HNO3

Assay (By acid-base titrimetry) Tare a small glass-stoppered flask containing about 15 mL of water. Quickly pipet about 2 mL of the sample under the water surface, stopper, cool, and weigh accurately. dilute with about 40 mL of water, add 0.15 mL of methyl orange indicator solution and titrate with 1 N sodium hydroxide. One milliliter of 1 N sodium hydroxide corresponds to 0.06301 g of HNO3.

I can verify that it is a good procedure as I was a member of the ACS Committee for Analytical Reagent Chemicals that wrote the book. Whether or not it is simple depends on your skills and access to some elementary lab equipment.

My advice is dilute it and get rid of it.

I was surprised at the amount of information as response to my query, I certainly appreciate it.

It appears that there is no easy and simple way to render a higher percentage grade and thus the extreme price differentiation. Vacuum Distillation seems like a good way to have a "problem".