Diluting 37% sulfuric acid to 0.12 normality

[priestie]

I need a .12N sulfuric acid solution for e-cigarette liquid nicotine strength testing, but .12N concentration is hard to get in my country.
I have battery acid at 37% solution (1.28kg/L), and have used some formulas to calculate mixing ratio, to get a .12N solution, but the testing doesn't add up.

I have used these formulas:
density ( g/L) x % by mass / 100 = g/L of H2SO4
g/L / 98 g/mol = molarity
N = Molarity x 2

I have calculated grams of pure H2SO4 in 1L .12N solution:
Molarity = .06
g/L = .06 x 98 = 5.88 g/L

And then calculated g/L in the 37% solution:
1280 x 37 / 100 = 473.6 g/L

Then calculating how many mL of 37% solution would contain 5.88g:
1000 / (473.6 / 5.88) = 12.42 mL

So, I measure 98.76 mL demineralized water and add 1.24mL of 37% sulfuric acid (making 100ml to test).

Testing a 72mg/mL nic base, gives me 64mg/mL concentration, so the resulting sulfuric acid solution seems to be to strong (I'm pretty sure the nic base is at 72mg/mL cause mixed e-liqud with the base matches strength of bought e-liquid at same strength).

What is going wrong?
Maybe measuring so small and precise quantities is to difficult, but I don't think that should give such far off results.

 

[Norrin]

But you don't know how accurate the 37% is. I think you are going to have to work the other way round and get your test liquid to the right strength from the nic. So when your 72mg is reading right test with a store bought 12mg or something and if that comes out close you have the right concentration.

 

[priestie]

But you don't know how accurate the 37% is. I think you are going to have to work the other way round and get your test liquid to the right strength from the nic. So when your 72mg is reading right test with a store bought 12mg or something and if that comes out close you have the right concentration.

Thanks for the reply, Norrin.
I have thought the same, but I don't think the 37% is off, cause its from a trusted supplier with data sheet and everything.
This is the product I'm using: Eurol Accuzuur | Eurol B.V.

I'm also considering working backwards, but it's totally unsatisfying not to be able to figure it out the "right" way.

 

[dannyv45]

I need a .12N sulfuric acid solution for e-cigarette liquid nicotine strength testing, but .12N concentration is hard to get in my country.
I have battery acid at 37% solution (1.28kg/L), and have used some formulas to calculate mixing ratio, to get a .12N solution, but the testing doesn't add up.

[

PM Dvape on this forum. He developed a nicotine test kit that is very widely used in testing on this forum.

He will likely be able to help you.

http://www.e-cigarette-forum.com/forum/members/16559/dvap.html

 

[priestie]

PM Dvape on this forum. He developed a nicotine test kit that is very widely used in testing on this forum.

He will likely be able to help you.

http://www.e-cigarette-forum.com/forum/members/16559/dvap.html

Thanks dannyv45. I'll send him a request, and link to the thread.

 

[dannyv45]

also look at this post maybe there's something that will help you.

http://www.e-cigarette-forum.com/fo...est-determining-nicotine-dvap.html#post549126

 

[priestie]

also look at this post maybe there's something that will help you.

http://www.e-cigarette-forum.com/fo...est-determining-nicotine-dvap.html#post549126

Super!
Long thread, but I'm reading on
The testing procedure itself is pretty clear, but it would be nice to get DVap's take on the dilution procedure.

 

[priestie]

Maybe some on could advice me a supplier in Europe, who sells acid in ready made concentration for e-liquid nic strength testing?
Should be shipping to Denmark, of cause.

I have found a supplier in the states, but that usually takes a long time in transit.
The most satisfying would be to mix the solution my self

Yesterday evening I just tried to mix a new batch of dilluted acid, taking more care to messure correctly, but I get excatly same results as the batch before. So atleast there are som consistency.

 

[MarkyD]

Have you looked for 0.1N hydrochloric acid (HCL) instead of sulfuric acid? Although either will work, 0.1N HCL might be easier to obtain. I dont know of an EU supplier but wizard labs sells nicotine test kits, bromothymol blue (ph test solution) and 0.1N HCL solutions. The test kits are sold out but the 4oz HCL and 12ml bromothymol blue are in stock. Instructions according to DVap's methodology are given on the site under the description of the test kit.

 

[priestie]

Have you looked for 0.1N hydrochloric acid (HCL) instead of sulfuric acid? Although either will work, 0.1N HCL might be easier to obtain. I dont know of an EU supplier but wizard labs sells nicotine test kits, bromothymol blue (ph test solution) and 0.1N HCL solutions. The test kits are sold out but the 4oz HCL and 12ml bromothymol blue are in stock. Instructions according to DVap's methodology are given on the site under the description of the test kit.

Thanks Marky. Unfortunately, WizardLabs does not ship out of country
I have also looked for HCL, but it's difficult to find.

 

[MarkyD]

I got to thinking about your 0.12N versus the 0.1N HCL I've used... While the 0.1N can be more accurate, and DVap's method works with either, there is a possibility for error in the final calculation of nicotine strength when using one versus the other. The Wizard Labs instructions are here:

Nicotine Test Kit

In the NOTE: section near the top it states: "This test kit can also be used with storebought 0.12N acid as a substitute, but in the step below for determining total nicotine content, you will need to multiply the final amount of acid used during titration by 19.471 instead of 16.223 to find the total amount of nicotine present."

Could be why your calculated strength is coming out too low.

 

[priestie]

I have been thinking, that maybe the nic base I'm "calibrating" against is not 72mg/mL after all.
Comparing my DIY liquid with store bought, I have been having same experience strength-wise, but that could just be wishfull thinking, and biased comparison.

If the formulas and calculation are correct, I really can't find anything wrong. I could be doing the nic test wrong, but I find that highly unlikely. I'm using the procedure and calculations from this ECF thread: http://www.e-cigarette-forum.com/fo...st-mg-ml-nicotine-follow-up-dvaps-method.html
I have tested the (presumed 72mg/mL) nic base at 64mg/mL, two times, with two different H2SO4 batches. Thats nealy inside a +/-10% boundary, but still a bit dissapointing. The higher the concentration, the more units you miss, per percent point, so I find 10% pretty high, in this case.

I need to be sure the test is good, cause I have a case going with a nic base supplier, who delivered colored and aromatic nic base, that I have testet to be way lower than the last batch I recieved, from a different supplier (the nic base I presume is 72mg/mL). So any way around, the latest supplier is WAY off the mark.

Any way of testing the sulfuric acid?

I'm really in the dark, atm

 

[priestie]

I got to thinking about your 0.12N versus the 0.1N HCL I've used... While the 0.1N can be more accurate, and DVap's method works with either, there is a possibility for error in the final calculation of nicotine strength when using one versus the other. The Wizard Labs instructions are here:

Nicotine Test Kit

In the NOTE: section near the top it states: "This test kit can also be used with storebought 0.12N acid as a substitute, but in the step below for determining total nicotine content, you will need to multiply the final amount of acid used during titration by 19.471 instead of 16.223 to find the total amount of nicotine present."

Could be why your calculated strength is coming out too low.

Thanks for the heads up. And good suggstion.
But I am using the 19.47 constant all ready. See post #12.

 

[MarkyD]

I have been thinking, that maybe the nic base I'm "calibrating" against is not 72mg/mL after all.

That remains a very real possibility, and was one of the reasons I ever tried testing. I found offsets from stated strength in the range of 1-2mg/ml, attributing some of that to eye-error in that the accuracy of the test is dependent on halting the addition of acid as soon as the solution changes from green-yellow to yellow. A 10% error does sound high.

 

[priestie]

That remains a very real possibility, and was one of the reasons I ever tried testing. I found offsets from stated strength in the range of 1-2mg/ml, attributing some of that to eye-error in that the accuracy of the test is dependent on halting the addition of acid as soon as the solution changes from green-yellow to yellow. A 10% error does sound high.

Yes, it more and more appears so. What error margin would you consider aceptable from 72mg/mL base? I would say anything lower than 68mg/mL would be unacceptable, if the base is fresh.
So, it would appear that I have been short-sold from both suppliers, but the latest, testing below 50mg/ml, would be unacceptable, for sure.

Still not convinced the sulfuric acid is right at .12N.

 

[MarkyD]

Something you alluded to in your OP is that errors in dilution and measuring can have a cumulative effect later on. These could be eliminated by measuring by weight instead of having to convert and measure things volumetrically. Also question how accurate that 37% original solution was, maybe for batteries a 1% error is tolerable, but for this its not.

 

[priestie]

Something you alluded to in your OP is that errors in dilution and measuring can have a cumulative effect later on. These could be eliminated by measuring by weight instead of having to convert and measure things volumetrically. Also question how accurate that 37% original solution was, maybe for batteries a 1% error is tolerable, but for this its not.

True. I have thought about using weight instead of syringes to measure. I think I got a high precision digital scale some where.
A 1% point differenc on the 37% wouldn't mean a lot in this setup. When adding the acid, the 1% i spread out in the 98.76mL water. Don't think that would effect the result much. I could be wrong in my assumption, though. more than 3% would probably be more concerning. But maybe I should try another supplier of battery acid.

But, thanks for the suggestions. Makes me think. Thanks

 

[priestie]

Update.
I just bought some 24mg at the store. It tested at 20.4. If I can trust the supplier, there is something wrong with the acid concentration.

 

[DVap]

I need a .12N sulfuric acid solution for e-cigarette liquid nicotine strength testing, but .12N concentration is hard to get in my country.
I have battery acid at 37% solution (1.28kg/L), and have used some formulas to calculate mixing ratio, to get a .12N solution, but the testing doesn't add up.

I have used these formulas:
density ( g/L) x % by mass / 100 = g/L of H2SO4
g/L / 98 g/mol = molarity
N = Molarity x 2

I have calculated grams of pure H2SO4 in 1L .12N solution:
Molarity = .06
g/L = .06 x 98 = 5.88 g/L

And then calculated g/L in the 37% solution:
1280 x 37 / 100 = 473.6 g/L

Then calculating how many mL of 37% solution would contain 5.88g:
1000 / (473.6 / 5.88) = 12.42 mL

So, I measure 98.76 mL demineralized water and add 1.24mL of 37% sulfuric acid (making 100ml to test).

Testing a 72mg/mL nic base, gives me 64mg/mL concentration, so the resulting sulfuric acid solution seems to be to strong (I'm pretty sure the nic base is at 72mg/mL cause mixed e-liqud with the base matches strength of bought e-liquid at same strength).

What is going wrong?
Maybe measuring so small and precise quantities is to difficult, but I don't think that should give such far off results.

Here's where you went off the rails:

And then calculated g/L in the 37% solution:
1280 x 37 / 100 = 473.6 g/L

I have no idea where you pulled the 1280 figure from. [Edit: actually, I do know. You used 1.28 g/mL as the density for sulfuric acid instead of the correct 1.84 g/mL]

The density of pure sulfuric acid is 1.84 grams/mL

Grams per liter in pure sulfuric acid is 1840. Grams per liter in 37% acid is 1840 grams * 0.37 = 680.8 (not 473.6 grams).

Also, don't make 100 mL of 0.12N acid solution, it makes the volume of 37% acid to add too low for a really accurate measure unless you have some more advanced equipment. Make 1 liter of 0.12N acid solution instead.

The molecular weight of sulfuric acid isn't 98 grams per mole, it's 98.08. It's only about a 0.1% error, but let's use the right value.

With sulfuric acid, 0.12N is 0.06M due to the acid being diprotic. So to make a liter of 0.12N sulfuric acid, you need 98.08g * 0.06 = 5.88 grams of pure sulfuric acid.

Now we're down to the crunch. Since the 37% acid contains 680.8 g/L of sulfuric acid, how many mL of 37% acid do we need to get 5.88 grams of sulfuric acid? That's just ((5.88 / 680.8) * 1000) = 8.636 mL of 37% sulfuric acid.

So, you would add 8.64 mL of 37% sulfuric acid to 250 mL of distilled or deionized water and mix. Then top off the solution to 1 liter with water, mix and serve.

Analyzing your results with the incorrectly made acid, you need to multiply all your nicotine concentrations by 1.4375 to get the actual concentration. So your 72 mg that tested at 64 mg would be 92 mg. Your 24 mg that tested at 20.2 mg would be 29 mg. Clearly something isn't right. That something is most likely the assumption that the 37% sulfuric acid you bought is really 37% sulfuric acid. It's looking more like it's considerably lower, maybe 26% or so. I've seen battery acid formulations that run as low as 25% and as high as 37%. Really depends on the manufacturer.

It's not a rule, but it's generally held true in my experience that muriatic acid (hydrochloric acid) available in hardware stores for driveway cleaning and such is much more accurately made. I've got a gallon of 31.45% muriatic acid. Since concentrated 37% hydrochloric acid is 12.1M, 31.45M hydrochloric acid would be 10.285M. I tested this stuff and it came out to 10.2M, barely a 1% error.

Somebody check my math, its late and I flew from the West Coast to the East Coast earlier today so I'm extra tired.

 

[MarkyD]

Here's where you went off the rails:

And then calculated g/L in the 37% solution:
1280 x 37 / 100 = 473.6 g/L

I have no idea where you pulled the 1280 figure from. [Edit: actually, I do know. You used 1.28 g/mL as the density for sulfuric acid instead of the correct 1.84 g/mL]

The density of pure sulfuric acid is 1.84 grams/mL

Grams per liter in pure sulfuric acid is 1840. Grams per liter in 37% acid is 1840 grams * 0.37 = 680.8 (not 473.6 grams).

And it would be that easy if the 37% v/v H2SO4 started with 100% H2SO4 and simply diluted it to 37%, but it doesnt, it uses 96% w/w and dilutes it to 47.64% v/v. I find msds sheets that list both 1.28 and 1.37 g/ml densities, depending on the initial concentration of H2SO4.

http://www.labchem.com/tools/msds/msds/LC25620.pdf