This is topic Anybody Good at Chemistry? in forum Film-Yak at Film-Tech Forum ARCHIVE.


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Posted by Randy Stankey (Member # 64) on 12-23-2018, 04:39 PM:
 
I'm now working as a lab tech in an electroplating shop.

A main part of my job is to keep the chemistry of the baths under control. (i.e. Performing tests and making additions to ensure that the solutions are up to par.)

Most of the time I perform tests according to what's laid out in our procedure manual but there are a few baths that don't have any tests laid out in the procedure manual. Basically, when the bath stops working, we dump it and make up new chemistry.

I guess that's okay but it can be expensive to throw out chemicals when you don't have to. Besides, waste treatment is a big P.I.T.A!

We have one bath made up from ammonium bifluoride and hydrogen peroxide that is used to strip tin from steel. Flushing ammonium bifluoride down the drain is a big no-no. It has to be treated first. The only reason the bath goes bad is because the hydrogen peroxide degrades over time.

I discovered it's possible to titrate for the concentration of peroxide using potassium permanganate. So, I did the math and figured up a procedure that works. Now, instead of dumping 50-plus gallons of peroxide/bifluoride solution down the drain, I can use the titration to figure out how much peroxide is needed to bring the bath back into spec. We can probably double or even triple the life of the chemistry and, thereby, reduce our waste by a third or more and save money on chemicals to boot.

Problem is, I don't have a degree in chemistry. I took chemistry in college and I did fairly well at it but that was over 30 years ago. I'm really rusty!

In order for my test to be included in the procedure manual, it has to be validated. I can get it validated if I take it to one of the professors I know from the Chemistry Department when I used to work at Mercyhurst University but I have to have everything written up, T's crossed, I's dotted and all the math has to be correct. The prof. won't sign off if it's not all correct and ready to go.

I've done the write-up with all the theory and calculation that I think is necessary. I've written down a step-by-step procedure. All I need to do is perform some validation trials with peroxide solutions of known concentrations and compare them to the expected outcome.

Before I go to the trouble and expense of making 20 titrations to validate the procedure, I'd like to have somebody look over my work.

Does anybody, here, understand this?...

5 H2O2 (aq) + 2 MnO4- (aq) + 6 H+ ==> 5 O2 (g) + 2Mn2+ (aq) + 8 H2O (l)

Would you like to look over my work before I potentially waste a lot of time and chemicals on a test that doesn't work?

Reagent grade KMnO4 solution costs about $25.00 a liter.
 

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Posted by Frank Cox (Member # 6258) on 12-23-2018, 09:12 PM:
 
I thought about putting a chemistry joke here but the last time I tried that there was no reaction.

I guess it was boron.


 

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Posted by Jim Cassedy (Member # 4115) on 12-23-2018, 10:45 PM:
 
I'm afraid I can't help with your problem. This is all I remember
from chemistry classes. I had an instructor who was a teacher by
day, and a comedian at night. So he combined both vocations-

Two chemists walk into a bar.
One says, “I’ll have an ‎H2O.” The other says,
“I’ll have an ‎H2O, too.” The second chemist dies.

If somebody throws sodium chloride at you,
... is it a salt?

What is Iron Man's favorite amusement park ride?
> A ferrous wheel!

Johnny was a nice boy,
but now he is no more;
cuz what he thought was H20,
was H2S04

I could tell you some jokes about the Periodic Table,
but I'd be out of my element...

What do you do if nobody laughs at your chemistry jokes?
> Keep trying till you get a reaction.
 

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Posted by Marcel Birgelen (Member # 6801) on 12-24-2018, 12:16 AM:
 
I'm not going to pretend to be good at this, but once in a while, I needed this damn thing called Chemistry to solve some puzzles.

Not pretending to know anything particular about your specific solution either, I came up with this:

Let's put the hydrogen peroxide into water, which is still pretty simple. It will yield the signature H3O+ couples that make up our acidy solution. In your case, this is what you already should have in your existing solution, which you're going to pimp, but at least it explains where the "H+" (or rather H3O+) came from:

(1) H2O2 (aq) + H2O (l) => HO2 (aq) + H3O+ (aq)

Then we're going to dissolve the potassium permanganate into the water, leading to a nice pink solution. Since it's not a simple salt, but a more complex compound, I had to look this one up, but apparently, it dissolves in water like this:

(2) KMnO4 (s) + H2O (l) => K+ (aq) + MnO4- (aq) + H2O (l)

So, then we're probably getting to the business end of things, although I'm not really sure what has been achieved in the end. The next one should be a redox reaction, based on all the agressive stuff in the water. If you see actual bubbling occur, let's hope it's actual O2 which is escaping.

(3) 2 MnO4- (aq) + H3O+ (aq) => 2 O2 (g) + Mn2H (aq) + H2O (l)

I guess that this Mn2H thing is pretty unstable in water and henceforth will probably end up like:

(4) Mn2H (aq) + H2O (l) => Mn2- (aq) + H3O+ (aq)

Disclaimer: Monday Morning armchair Chemistry at work here.
 

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Posted by Leo Enticknap (Member # 534) on 12-24-2018, 12:44 AM:
 

quote: Randy Stankey

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I'm now working as a lab tech in an electroplating shop.

A main part of my job is to keep the chemistry of the baths under control.

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quote: Randy Stankey

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We already know that it takes 2 moles of KMnO4 to react with 5 moles of H2O2 so that means the two substances react at a 1:2.5 ratio... For every 1 unit of permanganate you need 2.5 units of peroxide.

From this point, it's all just high school algebra.

So, let's say that I've done my test and I know that there is 100 ml/L of peroxide in the solution. The bath is supposed to have 125 ml/L of peroxide. That means I have to add another 25 ml/L of peroxide.

The processing tank contains 150 L and I need another 25 ml/L so that means I need to add 3.75 litres to bring the bath back into spec.

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quote: Courtesy of publichealthontario.ca

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C1 x V1 = C2 x V2

C1 is the initial concentration of the bleach (sodium hypochlorite) solution.
V1 is the volume of the bleach to be diluted with water. This is what you are trying to calculate.
C2 is the concentration of the diluted bleach solution you are preparing.
V2 is the volume of bleach solution you are preparing.

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quote: Martin McCaffery

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Everything I know about chemistry I learned from Tom Lehrer

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Love his sarcasm. Had great albums!
 

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Posted by Randy Stankey (Member # 64) on 01-06-2019, 11:37 AM:
 
I ran some trials to test things out and, now, I've got more questions.

I made up 3 samples of stock hyrogen peroxide diluted in distilled/deionized water: 50 ml./L. - 100 ml./L. - 200 ml./L.

I used 100 ml. volumetric flasks and volumetric pipettes to make up the test samples. (These should be accurate to 0.1%.)

I titrated each sample three times then averaged the results.

I got the following results:
Sample 50 ml./L. -- Titrant = 6.10 ml. -- Result = 52.45 ml./L.
Sample 100 ml./L. -- Titrant = 12.15 ml. -- Result = 104.47 ml./L.
Sample 200 ml./L. -- Titrant = 24.00 ml. -- Result = 206.36 ml./L.

That's almost 5% error! I was really confused until I went back and looked at the Certificate of Analysis for the batch of peroxide that I had used.

The C. of A. said that the stock solution that I used was 35.8% instead of the 35.0% that I had originally done my calculations with. (The grade of peroxide that we buy can be between 35.0% and 35.8%)

If I go back and adjust my math to account for the difference, my error goes down to 1.6%. That's not too terrible. I'm working in a grungy factory, not a university research laboratory. This is probably as accurate as it is possible to get under the conditions I have to work.

My question is whether I should change my calculations to the new numbers or leave them at the theoretical numbers I started with. I'm leaning toward leaving them as-is because, as the concentration of the stock solution varies, I want the test to account for that. (i.e. If I'm supposed to have 125 ml./L. of peroxide in my working solution but the supplier sends a different batch which has a different concentration, I'll have to adjust the amount of stock solution that I use to get the working concentration I want.)

If I want this to be any more accurate, I would probably have to go out and buy a bottle of hydrogen peroxide standard and run my trials again and this time, I'd probably have to do ten trials instead of three.

Aside from the time and expense, I don't think I'd be able to get any better than what I have already done under the conditions I work. I think it's better to say it's good enough and be done.

What do you think?
 

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Posted by David Buckley (Member # 2600) on 01-06-2019, 01:11 PM:
 
You need to figure out how accurate you need to be.

In the original post you say "the bath goes bad" - how do you know it goes bad? Is it determined by some test, by visual examination ("it looks yucky") or you run a batch and it doesn't work. That should lead you to an answer. It may be that you actually only need to have a concentration between x%-ish (which works) and not lower than y% (which doesn't), and then have some margin of accuracy in there. The chemistry and thus result wont be exact, but you'll still not be dumping gallons of stuff down the drain all the time.

The other thing I'd mention is that you can get hydrogen peroxide test kits off the shelf (first google hit) so you don't need to invent this wheel from scratch. Real time electronic measurement is also possible, though not as cheap as a test kit!
 

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Posted by Randy Stankey (Member # 64) on 01-06-2019, 02:29 PM:
 
We looked at a test kit like that. The problem is that its range only goes up to 10 mg./L. The concentrations we use are more like 5 g./L. We'd blow that test kit right off the end of the scale.

We actually have a lab with all the stuff needed to do most lab tests we need. I run titration tests for hydrochloric acid, cyanide and other stuff on a daily basis. There should be no reason why I can't run a test for peroxide, just the same way.

We use the peroxide in a solution used to strip tin from steel. If parts need to be reworked, they often have to be stripped down to the base metal and replated with tin. We use a solution with ammonium bifluoride, peroxide and a little bit of secret sauce to strip off the tin before replating.

As you know, hydrogen peroxide degrades pretty quickly. When it does, the tripping solution goes flat and won't work. When it stops working, we either have to throw it our or spike it up with more peroxide.

We have to be careful when throwing this solution out. Ammonium bifluoride makes hydrofluoric acid when mixed with water. We can't dump HF down the drain. It has to go through a complex waste treatment process before it is released to the sewer.

Besides, I'm the guy who has to dump out 50 gallons of this stuff, clean the tank and refill it with 50 lbs. of ammonium bifluoride and 5 gallons of peroxide.

If all that is necessary is to add some more peroxide to keep this solution working then it saves a lot of work for me, a lot of trouble in waste treatment and it saves money when we don't have to buy the chemicals.

Previously, we had been dumping this stuff and replacing it. I'm the one who came up with the idea of saving it by adding more peroxide.

The idea for the test is to determine how much peroxide to add to bring it up to spec. (16 oz./gal. or 125 ml./L.)
 

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Posted by David Buckley (Member # 2600) on 01-06-2019, 03:56 PM:
 
Yeah, that is some serious concentration of H2O2. You'd have to dilute it a lot to get it to within a test kit range and then you've done half the job of getting it to the titration anyway.

Even though my first career was as a hospital lab tech, it was many decades ago, and my chemistry is all but gone.

I don't envy you with the risk of HF acid forming; that stuff is truly scary.
 

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Posted by Randy Stankey (Member # 64) on 01-06-2019, 07:11 PM:
 
Luckily, I haven’t had any run ins with HF. We don’t stock HF directly. We use the ABF to create it in solution. By that time, it’s fairly dilute.

I did have a close call with some pure (96% reagent grade) sulfuric acid, however. I got splashed when some of it went under my face shield. I’ve got some pretty cool looking scars on my neck to show for it.

I’m not a great chemist, either. Just what I learned in high school and college.
I was lucky because my chemistry teacher from high school worked on the Manhattan Project and he wasn’t one for teaching strictly by the book. I wish he was still around!

I haven’t run into very many problems that are out of the range of a college chemistry course but, like you, I’m pretty rusty.

I think I’m going to stick with my original calculations because if the concentration of the stock solution varies I’ll need to add less Or more peroxide to achieve the spec. concentration.

After this, I have to come up with a way to determine the concentration of potassium monopersulfate (A.K.A. “Oxone”) in a solution because we have a surface activation bath that uses Oxone and sulfuric acid.

That’s going to be an iodine based reaction. It’s pretty funky but we already use an iodometric titration to test for stannous tin. I won’t have to develop the whole test but I will have to do the calculations and write them up.

This test for hydrogen peroxide is sort of a warm up for that one.
 

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Posted by David Buckley (Member # 2600) on 01-06-2019, 08:36 PM:
 

quote: Randy Stankey

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I did have a close call with some pure (96% reagent grade) sulfuric acid

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That's brought back a surpressed memory, we used to pipette something similar to that, and I got a mouthful of it one day. Makes your teeth fizz. Most unpleasant...
 

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Posted by Randy Stankey (Member # 64) on 01-06-2019, 09:29 PM:
 
Dude! Use a pipette bulb!

I regularly work with cyanide. (Potassium cyanide, sodium cyanide, copper cyanide and a few exotic ones like gold cyanide.) I would never even consider pipetting by mouth!

Right, at this very moment, there is a skid that has twelve 25 kg. drums of KCN. Just to give you a sense of gravity, that's enough to kill 1.5 million average size men or to put 3 million men, gravely ill, in hospital.

Point I'm making is that we don't fuck around with chemicals where I work.

What the hell could you have accidentally pipetted into your mouth?

If it was reagent grade sulfuric acid, you probably would be able to speak for the rest of your life, at least not without a speech impediment. That assumes that you lived through it.

Sulfuric acid reacts exothermically (and sometimes violently) with water. One of the jobs I have to do is to add it to one of the plating baths. If you add a gallon of H2SO4 to a 100 gallon tank of water you will raise the temperature a couple-three degrees in less than a minute.

If you got concentrated sulfuric in your mouth it would instantly boil the water in your saliva and cause severe burns and blisters. It wouldn't just make your teeth fizz. Your teeth would be corroded down to nubs in a very short time.

When I got burned by H2SO4, I was pumping it out of a 55 gal. drum with a siphon pump. The hose slipped and fell on the ground. In the process, some of the residual acid in the hose flung out and splashed me. When the hose hit the ground, acid splashed upward. Even though I was wearing a chemical apron, gloves up to my elbows, boots up to my knees, eye goggles and a face mask, the stuff came up under the mask and hit me in the left side of the neck.

I felt the stuff hit and I thought, "Oh, shit! This is going to hurt!" No sooner did I complete the thought the acid started to burn and I headed for the emergency wash station.

That stuff was on my skin for less than 30 seconds and I still got blisters and scabs. It took almost a month to completely heal but I still have scars.

Now, when guys get to drinking and boasting about their injuries and scars, I've got the sure winner. Right?
(C'Mon! We've got to laugh about things like this or we wouldn't survive life. Right? )

If you would have gotten acid in your mouth, you wouldn't be laughing, right now... because you probably wouldn't be able to laugh.
 

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Posted by Louis Bornwasser (Member # 3063) on 01-09-2019, 11:49 AM:
 
There should be no shortage of "consulting engineers" who are Chemical Engineers. This is why those guys have to take State licensening exams. Hire the consult on a one-time basis. Legally, it is the right thing to do for your company, paper work in order, signed off by a pro who does this kind of work. Your insurance company, if they knew, would demand it. Be careful at work; a circuit board company I know eventually had to close due employee chemical damage.
 

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Posted by Randy Stankey (Member # 64) on 02-22-2019, 08:38 PM:
 
Just an update...

I have been using the test for over a month, now, and it's working out well.

I made a fresh tank of chemicals on January 8th, performed regular tests at least once per week and made additions of peroxide as the tests indicated. The bath lasted until today when I finally had to change it out and make a new batch.

That's over six weeks on the same batch when, before, we were making a new batch almost every week.

Since a fresh batch of solution uses 90 lb. of Ammonium Bifluoride (Cost: $250/50 lb. bag) we've saved over $2,500 in chemicals, alone. Furthermore, it takes a whole 50 lb. bag of lime to neutralize a like amount of ABF. Don't forget the time and trouble of disposing all that waste.

I think this whole experiment turned out pretty well.
 

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