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"Determine % Nitric Acid. Titration? Conversion factor?"



Current question:

October 6, 2021

Q. Hi Mark,

Can you explain where you got the 0.65 factor for 70% Nitric Acid?

Thanks!

Casey George
- Fall River Massachusetts
^


October 7, 2021

A. Hi Casey,
The factor comes from a method in 'The Canning Handbook', page 935.
It is a well known old publication on electroplating.
It is no longer in print, but old copies can be found via ebay etc from time to time.
The factor is adjusted for a 10ml solution sample.
The 0.65 factor is used if you are topping up your tank with 70% wt/wt nitric acid, S.g. 1.41.
If you are topping up with 60% wt/wt nitric acid, S.G. 1.37, then the factor becomes 0.76.
I hope this helps.
best regards
Mark

Mark Lees
- A foresaken rock in the irish Sea
^


"The Canning Handbook of Surface Finishing Technology"
from Abe Books
or

Affiliate Link
(finishing.com earns a commission on whatever you buy after clicking)
or
see our Review

October 2021

A. Thanks Mark. The Canning Handbook is now apparently available as a paperback through Amazon (not vouching for the paperback publisher) or a Kindle e-book. They claim to be the 23rd edition, which was published in 1982 (my hardcover is 23rd edition).

41654-2

Readers: I read some reviews that said this is not a great plating book for a number of reasons including being outdated and relying heavily on proprietary names. My comment is that, indeed, it's not a good first & only book for those reasons and more ... but if you have a couple of others it's a great one :-)

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related Q&A's, oldest first:

2006

Q. If I have a solution of unknown Nitric Acid, how can I test that solution to determine that percentage of Nitric Acid?

Kimberly NeVille
aerospace - Ogden, Utah, United States
^


simultaneous 2006

A. Hi Kim,
If you work for an aerospace company and you use nitric acid, your company is supposed to have a chem lab or a qualified lab to do the testing.
When you say strength, you need to define it a bit more, as in percent of make up acid or percent of theoretical.
Also it can be measured in baumé or in specific gravity.
An old fashioned way is 10 ml of solution in 100 ml distilled water, a couple of drops of methyl orange indicator, titrated with 1N sodium hydroxide from a red to a yellow orange end point. Titrate slowly so you do not get a false reading from dissolved metals that precipitate out as hydroxides.
I like 1 ml sample in 50 ml distilled water and titrate with 0.1N sodium hydroxide. Uses less material and is less likely to get false readings from metal precipitation.
Tell us what units you want it in and someone will give you the fudge factor to multiply the mls of titrant by to give you the answer.

James Watts
- Navarre, Florida
^


2006

A. Kimberly,

If nitric is your only acid you should be able to easily titrate the solution to neutrality using a strong base solution of known concentration and then calculate your original acid strength. Any general chemistry textbook can give you more info or you should be able to see the calculations on the web.

Terry Tomt
- Auburn, Washington
^


2006

A. Titrate it against a known concentration of Sodium Hydroxide using a suitable indicator and calculate for the unknown.

Any indicator in the 4-8 pH range should be fine, the two chemicals should swing hard between the two pH extremes.

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA

accurate anodizing banner
^


2006

A. Jim, 8 is way too high a pH as metal hydroxides will form and not go back into solution in any reasonable time frame. Typically, pH's of 4 to 5 are used and have virtually no effect on the titration because pH is logarithmic.

James Watts
- Navarre, Florida
^


2006

thumbs up signJames - Thanks for the correction. Anyone in doubt: follow his statement, not mine.

Sorry for the mis-information.

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA

accurate anodizing banner
^


2006

A. If you want to check that which kind of acid is there you have given , then you pl first confirm it acid by titration with caustic and find out the acidity. Then add barium chloride, silver nitrate, and lead acetate [affil. link to info/product on Amazon], in three different test tubes, and add that unknown and neutralized acid one by one. Check for any precipitation.if it gives white precipitates with barium chloride then that acid may be sulphuric acid, if it gives white precipitates with silver nitrate then that acid may be hydrochloric acid.

Rakesh [last name deleted for privacy by Editor]
- Vadodara, Gujarat, India
^


2006

Q. James,

The solution of Nitric Acid I am measuring is simply Nitric Acid diluted with water. I am looking for a volume percentage of the solution. We currently test the acid tank and report it in oz/gal. However, somebody decided that we need to report it in percent. The dissolved metals will be titanium and stainless steel.

Kimberly NeVille [returning]
- Ogden, Utah, USA
^


2006

A. Kim,
Simple if you have fluid oz per gal. Convert gals to fluid oz. Divide fl oz of acid by fluid oz of a gal and multiply by 100 to get %.

James Watts
- Navarre, Florida
^



May 6, 2016

Q. We titrate our nitric acid bath using the following process:
- pipette 5 ml sample into 250 mL flask
- dilute to 150 mL with distilled water
- add 2-3 drops of Phenolphthalein Indicator (Gardotest indicator 2)
- gradually add 1.0N Sodium Hydroxide (Gardotest Indicator 37) using burette while swirling until solution turns pink
- record the number of mL of 1.0N Sodium, Hydroxide used=V
- calculation is %=1.334xV

The discrepancy we have here is the interpretation of the end point ... different team members determine it at different points but we want to have a fail safe instruction/colour point. Our colournormally changes to a yellow-orange not pink as per above. Is the end point just when the clear solution changes to yellow-orange or you keep adding the Sodium Hydroxide until it is very dark and doesn't change anymore? Any advise would be appreciated.

Barb Hulse
aerospace - Orangeville, Ontario Canada
^


simultaneous May 7, 2016

A. First things first, I'm not a chemist, but here's what I'd do:

I would make a small amount of a known solution concentration (your ideal concentration), and titrate per your established procedure. When the known solution reaches the colormetric endpoint, corresponding with the known concentration of the solution, measure the PH. Use that Ph reading going forward as your endpoint during your titration, as opposed to the color change. This takes the variability of color perception out of the equation.

Marc Green
Marc Green
anodizer - Boise, Idaho
^


May 8, 2016

A. I concur with Mr. Watts. pH 8 is too high. At that pH you're going to see a lot of NaOH uptake from the hydrolysis of transition metal ions.

Methyl orange is probably a better choice than phenolpthalein.

dave wichern
Dave Wichern
Consultant - The Bronx, New York
^


May 8, 2016

A. Phenolphthalein is probably the worst indicator that you could use if you have any dissolved metal in it. You need an indicator that changes color in the 4-5 pH range. Methyl red and methyl orange are frequently used. Some like one better than the other.
Second, you need to add the hydroxide very slowly as it will drop out the metals as hydroxides and they do not go back into solution very easily. I adopted using a smaller sample (with calibrated pipet) and titrating with 0.1 N hydroxide with spin bar agitation.
To get everyone on the same page, why not use a good quality pH meter to establish a color change point that everyone will accept.

James Watts
- Navarre, Florida
^


May 9, 2016

A. Hi Barb,
Try Bromocresol green, that gives a more defined end point than phenolphthalein, so there should be less room for discussion as to where the end point is.
Best Regards
Mark

Mark Lees
Aerospace - Isle of Man British Isles
^


simultaneous May 10, 2016

A. Bromcresol green is a good indicator. Look it up and see what the color change points are. My foggy memory says that it had 2. If so, use the lower one.

James Watts
- Navarre, Florida
^


May 10, 2016

A. The way I remember learning it, when you start to see the indicator changing color as the drop falls in and then immediately vanishing as it mixes, it's time to slow the drops way the heck down. Then, when the color changes all the way without reversing due to the mixing, that's the titration end point.

Of course, just using a pH meter works too as long as you're confident of the calibration.

If dissolved metals are interfering as James Watts suggests, you may need to precipitate them out beforehand with something that will not disturb the acid content.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner
^


May 10, 2016

A. Good day Barb.

I use phenolphthalein for my sulfuric anodize analysis, and it is tricky, as you must determine when there is no longer ANY colour change. I make up a known concentration of acid in a 100 ml volumetric flask and verify, it works for me.
For the nitric, try 1 ml in a 250 ml beaker, add 75 mls DI water, titrate with 1.0 N sodium hydroxide to pH 3.57, giving titre A. A stir bar on the magnetic hot plate gives good results, so titrate slowly. I found in my passivation solutions which do not contain iron or dichromate,pH values rise very slowly approaching 3.0, and then there is a quick spike.
You can use 0.1 N Na OH here, with the math.
Nitric acid in % BV = 6.45 X A
Nitric acid in g/l = 63 x A
Hope this helps.

Regards,

Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada
^


June 17, 2016

A. I agree that Bromocresol Green is the most user-friendly indicator for Nitric baths.
Personally I'm less of a fan of the Methyl orange color shift, as it goes through quite a color range on its way to salmon red.
Phenolpthalein definitely has its place in Sulfuric bath titration (and others). But as was alluded to earlier, by the time you hit the PTH endpoint, you're in the precipitation range for many metal hydroxides, and can easily get a false high reading if you're not prepared for them. In an anodize bath you take the hydroxides out BEFORE starting the titration (KF50% at a ratio of about 2 parts KF to 1 part bath aliquot); the difference between a treated and untreated sample is your aluminum value but that's another thread :)
You might notice that the pH endpoints are all vastly different, with MO around 4, BCG around 5, and PTH over 8... But once the acid is used up, the pH rises so rapidly that a minimal amount of titrant will cause it to skyrocket.
I agree also that it is an excellent habit to validate your titrations by creating a known standard and testing it. I did that with EVERY TANK when I took over my current lab. It's also a good instructional tool for new techs.

rachel_mackintosh
Rachel Mackintosh
Lab Rat - Greenfield, Vermont
^



October 12, 2016

Q. We titrate our nitric acid bath using the following process: (same as Barb Hulse above)
- pipette 5 ml sample into 250 mL flask
- dilute to 150 mL with distilled water
- add 2-3 drops of Phenolphthalein Indicator
- gradually add 1.0N Sodium Hydroxide using burette while swirling until solution turns pink
- record the number of mL of 1.0N Sodium, Hydroxide used=V
- calculation is %=1.334xV

Does anyone have a reference for the calculation? We do the same thing and have been asked for a reference to support our results. I am also going to look into changing our indicator as they suggested. The Phth endpoint is really tricky.

Thanks for your help.

Kati Owen
Aerospace - Niceville Florida USA
^


October 14, 2016

A. Hi Kate,
The indicator you should use is bromocresol green.
Also your multiplication factor looks like the one for sulphuric acid.
You should multiply your titre by 0.65. This works for a 10ml vat sample titrated with 1.0N sodium Hydroxide, and give you a result expressed as percent by volume of 70% (700g/l0 nitric acid. S.G. 1.41.
For 60% nitric acid use 0.76 as the factor.
I hope this helps, and good luck
Mark

Mark Lees
making stuff for aeroplanes - A rain soaked rock in the irish sea
^



October 16, 2018

Q. We have been using a semi-automated titration system for our daily measurements. The system requires a daily pH calibration using 1.68, 4.01, 7.00, 10.01 and 12.45 standards.
We then transfer these values to an Excel spreadsheet for tracking the solution and making well informed solution adjustments. We have had great success with all of the titrations except for the Nitric Acid in solution of the DEOX chemistry.

Our DEOX target is 96 g/L of (Fisher Scientific Nitric Acid 65-70%)in solution

Our test process is:
Pipette a 2 mL sample
Add DI water up to 100 mL
Auto Titrate with sodium hydroxide
Press 'Start' Titrator will titrate to pH 3.7 endpoint. Results will be displayed as g/L nitric acid.

This nitric acid titration is very difficult to get a normal looking graph over time. The graph is very noisy.

I have conducted testing of the same process tank DEOX chemistry. Duration of all five samplings 30 minutes.

The first titration sample was extracted using a drum thief sampling the cross section of the tank without stirring the tank.
The result of the first titration was done using this sample.
Titration # TI00664 = 85.167 g/L


A second sample was taken and the extraction method was the same, no stirring and the drum thief was used.
Three consecutive titrations were run using this sample.
Titration # TI00665 = 88.088 g/L
Titration # TI00666 = 87.118 g/L
Titration # TI00667 = 87.533 g/L
The average of these three titrations was 87.579 g/L and % of deviation between the three samples was 0.5%


A third sample was taken and the extraction method was the same, no stirring and the drum thief was used.
One titration was done using this sample.
Titration # TI00668 = 86.601 g/L

My take away from this exercise was the three consecutive titrations of the same sample were showing repeatability of the semi-automated titration system.

The sampling method showed greater variation pointing to the chemisty not being homogeneous. I have since started stirring the DEOX tank using a stainless steel mixing paddle every morning. Then wait 15 minutes and take my sample using the drum thief.

I have not been tracking my results long enough but the graph looks less noisy.

I then spoke to the manufacturer in regards to this and I was pointed back to the manual titration using the Bromocresol Green indicator method.

I would like to understand the sampling methods of others out in the field. Should I go back to manual titrations?
What is the best method for day to day sampling? Use a dipper, drum thief or other method?

The first graph is of the proprietary chemistry in solution. It is easy to see how tracking and making adds is intuitive.
The second graph is what I was seeing when measuring the Nitric Acid.

41654

Thank you All

Kurt Krueger
- Lexington, Massachusetts
^


October 16, 2018

A. Hi again Kurt!
I read your post with a bit of a smile... You're going to drive yourself nuts over your DeOx! :)
Please don't! No doubt you've allowed yourself a pair of working ranges (target +/- some amount recommended by the manufacturer or your own experience, and then a narrower range like a warning limit) and your most simple, basic, goal for accuracy of the titration is to make sure that your titration error won't ever be enough to make you THINK you're in shop range when you're not, and that your adds will be accurate.

Your titrator sounds pretty repeatable especially considering the small aliquot being tested; I'm impressed. Usually smaller samples mean more analytical error, and 0.5% is outstanding.

Don't sweat the 'noise' TOO much in your samples over time. It happens. Reduction, rather than elimination, of the noise is about the best you can ask for. There's a lot going on, chemically, in a DeOx tank, and every new load of parts dropping off a new load of smut is going to slightly (even imperceptibly) shift how a free acid titration presents at that moment- It's larger trends over time that matter, and I totally get how you'd like to see your Nitric results looking more like your first graph. It's a chemical crockpot in there and you are correct that a reduction in noise may be achieved by ideal sampling.

To answer your question about sampling- you mentioned you swirl the tank with a paddle? Do you really not have a mixer in that tank (sparge, rotary, or recirculating)? If the tank is mixed well enough to function correctly, a dipper right from a few inches below the surface is absolutely fine. Rinse the dipper in the DeOx and dump it out a couple times before taking the sample.

The takeaway is don't get too crazy chasing perfection in a DeOx tank of all places, and you really want to make sure your tank is well mixed both at time of drawing test samples and time of use for best results with both!

rachel_mackintosh
Rachel Mackintosh
Lab Rat - Greenfield, Vermont
^


October 17, 2018

thumbs up sign Hello Rachel

Thank you for the quick response, You brought a smile to my face... You provide a valuable resource.

I was trying not to go nuts with the DEOX measurements, I wanted clean data. But yes, this can consume you.
I will be performing the Bromocresol Green titration to determine the nitric acid in solution and in parallel semi-automated nitric acid potentiometric titration. Until I have confidence in my process. Almost there.

I was not continually stirring this DEOX tank. I was only stirring this tank in the morning manually. That will be changed, I will be installing a stirrer. This may be the part I was missing...

Thank You

Kurt Krueger [returning]
- Lexington, Massachusetts
^



April 26, 2019

Q. I am trying to test the nitric acid in my tank, what chemicals will I need with my titration kit to test the the wt percent in it with the copper, cobalt, iron, nickel and chromium.

Jevetta Siggers
pickler - Hernando, Mississippi, America
^


May 2019

A. Hi Jevetta. It's hard to offer good answers to a question until it is well understood. This pickling solution is straight nitric acid (no fluorides, sulfates, or other acids), and you would like a procedure for testing the wt percent of nitric acid ... but due to use it may be contaminated with those 5 metals? Or are you saying you want to know the procedures for measuring the nitric acid plus for each of those 5 metals? Is there a need for clarification or do you have questions or on any of the many comments already offered? Thanks!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


May 17, 2019

A. Hi Jevetta,
For accurate quantification of metals, especially at low or low-ish levels, running by plasma spectrophotometry is standard. Test kits can give a crude result at higher levels but aren't particularly accurate, and are prone to matrix interference- you'd have to buy one specifically for a Nitric matrix. The good news is that Nitric acid is actually the required preservative for metals samples in aqueous solutions, and won't interfere at all with plasma spectrophotometry. You would do well to call around to a water testing or other analytical lab and find out what they charge- be sure to tell them what your matrix is- I can guarantee that it is MUCH cheaper than trying to buy all the chemicals, equipment, and training literature you'd need (not to mention labor costs!) to quantify various metals in solution. I've worked as a chemical analyst for well over a decade so far and, not to discourage anyone from learning how to do tests, it's time consuming and expensive.

"Standard Methods for Examination of Water & Wastewater"
by American Public Health Association
from Abe Books
(including dirt cheap older editions)
or

Affiliate Link
(finishing.com earns a commission on whatever you buy after clicking)

If you really want to know, grab a copy of
<== Standard Methods for the Examination of Water and Wastewater, being sure it's an edition that was written AT LEAST as recently as the 1990s.

rachel_mackintosh
Rachel Mackintosh
Lab Rat - Greenfield, Vermont
^



October 28, 2019

Q. Is there any difference between using 1.0N or .5N sodium hydroxide as your titrant? We have an auto titrator to test for nitric acid concentrations. We have always used around .75g of acid, filled our cup to about 40ml and then started the titrator using the .5N sodium hydroxide. We have a few customers who use 1.0N and all the methods on-line show 1.0N. I want to make sure using .5N is okay for what we are doing.

Stephanie Boll
- North Bend, Ohio USA
^


November 15, 2019

A. Hi Stephanie,
If you use 0.5N on a titration that is calculated for 1.0, then logically you must then recalculate.

For example, if your titration used up 10.6 mL of 0.5N NaOH, it would have only used up 5.3 mL of 1.0N NaOH (because 1.0N is twice as strong as 0.5N) to reach the same endpoint.

Using a larger volume of a less concentrated titrant will increase resolution (though frankly plating-shop-floor titration is not a particularly precise branch of analytical chemistry lol) but you must remember to mathematically correct for any variation in titrant strength in your equations.

rachel_mackintosh
Rachel Mackintosh
Lab Rat - Greenfield, Vermont
^



September 11, 2020

Q. Hello everyone!

I've just built a production Passivation processing lab that'll serve the aerospace sector. I'm running Nitric Acid solutions in accordance with AMS2700 [affil. link to spec at Techstreet], types 2,6, and 8.

In a recent audit, we received a finding for not having a titration method that is traceable to a national standard or chemical manufacturer.

I've been performing this process and the required solution analysis for 15+ years. In all those years, I've never been asked, "where did you get your titration method from?"

It's the method I was taught when I came into the field.

The quick version: with a stirring sample, I drop in 7 drops of Bromphenol Blue Indicator Solution, then burette in 1.00N Sodium Hydroxide to a change in color. The mL of Sodium Hydroxide used is multiplied by 6.45 equaling the Nitric acid concentration by volume.

Unfortunately, I'm not a chemist, and have no idea where this method derived from. I've found the 6.45 multiplier in the string, does anyone know where that number, or the whole method for that matter, came from?

I'd like to continue with this method, since I have all of the goodies to do it, but am more than willing to entertain a new method.

You all have been a great resource!

I appreciate it!

Thanks!

Josh L.
- Plainwell, Michigan
^


October 8, 2020

"Vogel's Quantitative Chemical Analysis"
from Abe Books

or

Affiliate Link
(finishing.com earns a commission on whatever you buy after clicking)

A. Hi Josh L.

This is a nice question and there's an answer to it.
I also hope others will check the calculations and prove me wrong (or not)

You actually ask for an analytical chemistry course. I can recommend you A.Vogel's book about analytical chemistry.

I didn't see how much solution you pipette, but that's not too important for the first part of the answer:

The titration you do is an acid-base titration, whereby the reaction is:
HNO3 + NaOH -> NaNO3 + H2O.

The theory in this titration is relatively simple. It is what we call an acid-base titration, whereby you neutralize the acid with the NaOH till the point that your indicator changes color, which is also the moment that all the acid is neutralized by the caustic (NaOH).

In this case you're lucky as the reaction equation goes like: 1 mole of HNO3 reacts with 1 mole NaOH to give 1 mole NaNO3 and 1 mole H2O.

(The mole is used in chemistry and is the unit of measurement for amount of substance in the International System of Units (SI). A mole of a substance or a mole of particles is defined as exactly 6.02214076x10^23 particles, which may be atoms, molecules, ions, or electrons)

Using the periodic chart you can find all the atomic weights of a mole of your elements and so find the grams of HNO3 that react with the grams of NaOH and you can even find how many grams of reaction products you get.....
Let's Look it up:
H = 1,008 gram per Mole
N = 14,01 " " "
O = 16.00 " " "
Na = 22,99" " "
So that means:
HNO3 + NaOH -> NaNO3 + H2O.
63.018g HNO3 + 39.998g NaOH --> 85g NaNO3 + 18.016g H2O


I must hope that the NaOH you buy is from a certified supplier. That means that the amount of NaOH in the 1N solution is precisely weighted and dissolved to be exactly 1N NaOH. That way the whole titration is NIST traceable.
A 1N NaOH solution contains exactly 39.998g/l. NaOH if you buy a certified solution and as long as you keep the bottle tightly closed, that is true.
However, you should keep in mind that, if you open up the bottle and use it for a long time, some of that NaOH will change to carbonate and your solution will not be exactly 1N anymore. Therefor, if you do this titration not very often, you can check your 1N NaOH, by buying also another burette and fill it with a solution of 1N HCl.
If you now titrate a known volume of NaOH and use the same indicator and see if you need to titrate exactly the same amount of 1N HCl in ml to neutralize that NaOH solution (Indicator color change)you can check that NaOH standard in practice also.
If you find +/- 1% difference, I wouldn't be too concerned at all.

The next step is how you get to that 6.45 number and what it means.


I always prefer to express numbers in g/l or oz/gallons, as % HNO3 differs.

Let's assume that to increase your concentration, you add a solution of 50% HNO3 with a density of 1,310 g/l. (A well known industry standard)
As it is 50 mass %, it contains 655g/l. HNO3.

If I take a sample with a pipette of exactly 5 milliliter of this HNO3 solution, I have (655/1000)*5 = 3.275grams of HNO3 in that sample.

We have seen earlier that 1N NaOH contains 39.998g/liter
NaOH and that we can neutralize 63.018g HNO3 with that.

(HNO3 + NaOH -> NaNO3 + H2O.
63.018g HNO3 + 39.998g NaOH --> 85g NaNO3 + 18.016g H2O)

So this 5 ml sample that contains 3.275g HNO3 will need

(3.275/63.018)*39.998 = 2.0777g NaOH to be neutralized, or
(2.0777/39.998)*1000 = 51.95ml of a 1N NaOH solution.

As I don't know how much you pipette as a sample, I can't finish this for you, but I hope I gave you enough insight to do this yourself. If not, no problem, just ask.

Keep in mind that using "volume of HNO3" assumes that the HNO3 is always the same concentration, and I can guarantee you, it's not. Therefore, if your composition is critical, you better use the g/l. or oz/gallon calculation. If it is not, it doesn't matter too much, you probably have wide limits.

So to go back to your auditor's question: Due to the fact that you buy certified 1N NaOH standard solutions (not worth making them yourself, but you could if you had a good analytical balance and pure NaOH) and check them regularly with the 1N HCl solution, the outcome of this analysis is always guaranteed to be OK (as long as you have skilled people that do the titrations and you don't take shortcuts.) The latter you can test with an MSA.

Hope I didn't lose you. Sorry for my European units ...

Take Care,

Harry.

Harry van der Zanden
Harry van der Zanden
- Budapest, Hungary
^


October 8, 2020

thumbs up sign Hello Harry.

First, thank you for your comprehensive reply! It is sincerely appreciated!!!

You didn't completely lose me, I did have to "chop a couple branches out of the way" to keep up...

That said, I will be purchasing a copy of A. Vogel's book.

I thought I would fill in a couple of the missing numbers from my original post. You are correct, I do purchase all of my standards from a certified source. They are reagent grade, and traceable to NIST.

1.) The volume of the working solution sample that I pipette for analysis is 1mL, then diluted to 100mL with Distilled Water for the titration.

2.) The concentrated HNO3 I use in the working solutions is 70%, reagent grade. (certified assay is 68.0-70.0 w/w%)

Specific Gravity: 1.42
Normality: 15.8
F.W.: 63.01

3.) The HNO3 % concentration limits for the 3 working solutions I use are: 20-25%, 25-45%, and 45-55%.


You've given immense insight. But, to be completely honest, I could really use the help filling in the blanks. I hope I've given enough additional information to do so. Please let me know if I've missed something.

Again, I appreciate your insights! Priceless!

Thank you!

Best regards,

Josh L. [returning]
- Plainwell, Michigan
^


October 11, 2020

Hi Josh,

Thanks for your kind words, that motivates to continue....

Recap:
The reaction in that titration is:
1 Mole HNO3 + 1 Mole NaOH -> 1 Mole NaNO3 + 1Mole H2O.
Or (the moles converted into grams, using the periodic table atomic mass data)
63.018g HNO3 + 39.998g NaOH --> 85g NaNO3 + 18.016g H2O

So a certified 1 N NaOH solution, contains 39.998g NaOH
Your 70% (68 - 70), let's use 69% w/w HNO3 solution has a density of 1.42, which would mean 0.69*1420g/l. = 979.8g/l. HNO3

If you pipette 1ml and you need to find 6.45ml of 1N NaOH at the titration, than that 6.45ml of 1N NaOH neutralizes:
(6.45/1000)*63.018g HNO3 = 0.4065 gram of HNO3
Or that equals (as it is 1/1000th of a liter), a concentration of 406.5gram per liter HNO3 in your electrolyte.

Converting it into a volume % of 69% HNO3 would mean that the nominal composition = (406.5g/979.8g/l) = 41.5 volume % of a 69% HNO3 solution

If your target is 25 - 45%, you're good here.

But if your target is 45 - 55%, you're on the low side of the concentration.
In that case you would shoot for 50% by volume of a 69% (68-70) by weight nitric acid solution. (Density 1.42kg/l.)

As seen before, that 69% solution contains 69% of 1.42 = 979.8g/l. HNO3 and 50% by volume would contain 489.9g/l.
a 1 ml sample would contain 0.4899gram HNO3 if your solution were at exactly that 50%

Back to the general reaction:
63.018g HNO3 + 39.998g NaOH --> 85g NaNO3 + 18.016g H2O
That means that:
0.4899g HNO3 is neutralized by (0.4899/63.018)*39.998 = 0.31094g NaOH and as ml of 1N NaOH contains .039998g NaOH, you would need 7.77ml to be at the exact 50%.


In a similar way you can calculate your milliliters needed for a 20 - 25% v/v of the 70% solution.

One general advice, for those lower concentrated solutions (and actually also for the 50% one): you better pipette 3 ml of the solution. You don't want to be in a very low range with your burette, as your absolute fault in the reading remains the same over the whole burette range, but get's relatively pretty big if you titrate so little. Of course you need to change the factors too in that case.

Not being a passivation expert and it might be that people contradict me, but in general, the process window for passivating in HNO3 is pretty wide. +/- 20% concentration variation won't hurt, but you might not be able to start that discussion with an auditor without having your own evidence for that……

Good luck, hope this finally helps you out. Don't forget you've been doing this for 15 years an probably never had any complaint or problem, but alas, specification is specification and the AMS 2700 is what you have to live up to I guess.

Take Care,

Harry

Harry van der Zanden
Harry van der Zanden
- Budapest, Hungary
^



September 21, 2020

Q. HOW DO I CHECK STRENGTH OF NITRIC ACID AND GIVE ME FORMULA?

MD SAJID
- HYDERABAD & TELANGANA/WANAPARTHY, INDIA
^


October 2020

? Hi cousin MD. More words please! Despite this discussion spanning 14 years and 30+ postings, it may certainly still be deficient. But from your brief question, I can't tell in which way :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^

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