Diluting 37% sulfuric acid to 0.12 normality

[priestie]

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.

Thank you very much for the elaborate response, DVap.

The 1280g/L is from the manufacturers product homepage. I see now, that I propably misunderstood the formulas input definition. Isn't the formula "density ( g/L) x % by mass / 100 = g/L of H2SO4" meant to find the actual weight of H2SO4 molecules in solution?

I'm making smaller batches to sanity check the mixing. When I can mix 100mL with good results over a few trys, I'll mix one liter, to raise accuracy.

Funny thing, I actually reached that number, 8.64, myself, when trying to calculate by camparing and scaling N value for 95.8% solution, where I knew the N value. But that mix testet the nic base way to high, as you also predict it would.

So, the truth is some where in between (isn't it allways ).

I have written to the manufacturer to get some answers on the tolerance of the battery acid.
And maybe I should just buy som hydrochloric acid instead. That's also easier to find.

 

[DVap]

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

You can't have 37% vol/vol and also 47.64% in unspecified units, doesn't add up. Also, the general convention for percent solutions is wt/vol. This is one MSDS among many for sulfuric acid solutions and they're not all going to use the same units. I can't stomach the ambiguity. I'd avoid the whole mess by using a high quality white vinegar diluted to 5% acidity. The conventions here are well known and consistent:

A 5% solution of white vinegar is 0.832 molar and 0.832 normal. It's not a strong acid, but in this usage, it doesn't matter.

To make 1 liter of 0.12 normal acetic acid solution starting with 5% (0.832N) white vinegar is easy:

144.3 mL of vinegar to a final volume of 1 liter in distilled water.

 

[priestie]

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

I understand now, that I should have been a more diligent student through chemist class at high school

Could I measure a precise amount of the acid, and weigh it, coulden't I then get a better hint at the percentage?

 

[priestie]

You can't have 37% vol/vol and also 47.64% in unspecified units, doesn't add up. Also, the general convention for percent solutions is wt/vol. This is one MSDS among many for sulfuric acid solutions and they're not all going to use the same units. I can't stomach the ambiguity. I'd avoid the whole mess by using a high quality white vinegar diluted to 5% acidity. The conventions here are well known and consistent:

A 5% solution of white vinegar is 0.832 molar and 0.832 normal. It's not a strong acid, but in this usage, it doesn't matter.

To make 1 liter of 0.12 normal acetic acid solution starting with 5% (0.832N) white vinegar is easy:

144.3 mL of vinegar to a final volume of 1 liter in distilled water.

Ok. I think I'll call the battery acid a loss, and find another acid to use.
I don't know where to get 5% white vinegar. I can get hold of 32% Acetic acid and 30% Hydrochloric acid. Which one would fit best? I also have som citric acid powder, but the purity of it is unknown.

I really would like to have som trust worthy numbers to throw at the supplier, whoes product quality I'm gonna question.
I really appreciate you efforts. Thanks a lot!

 

[MarkyD]

Trying to unconfuse myself now, but I think I get what DVap is saying is that componenent percentages given in the MSDS are either wt/vol or arbitrary numbers. The question is the same as priestie is asking...

Isn't the formula "density ( g/L) x % by mass / 100 = g/L of H2SO4" meant to find the actual weight of H2SO4 molecules in solution?

For some reason, that looks correct to me, and I wouldve plugged in the density of the 37% solution converted to litres in there as well (1.28*1000).

 

[priestie]

Ok. I think I'll call the battery acid a loss, and find another acid to use.
I don't know where to get 5% white vinegar. I can get hold of 32% Acetic acid and 30% Hydrochloric acid. Which one would fit best? I also have som citric acid powder, but the purity of it is unknown.

I really would like to have som trust worthy numbers to throw at the supplier, whoes product quality I'm gonna question.
I really appreciate you efforts. Thanks a lot!

I see now, that ordinary vinegar you buy in 1-5L containers in Denmark are what you are talking about. I found a danish page that stated the percentage of house hold vinegar (thats what its called in Denmark) as 5%. So that's probably what you are talking about.
I'll give it a shot and leave a post with the results.

Thanks again.

 

[priestie]

Okay. Now I'm in business

New test results:
Nic base bought in may, rated at 72mg/mL - 72.04
E-liquid bought yesterday in store, with flavour at 24mg/mL - 23.36
Nic base bought 14 days ago, rated at 72mg/mL - 42.83

I definitely has a case against the new supplier.
I used white vinegar from the kitchen shelf. Its probably a year old, or so, but it seems pretty spot on.

I would like to thank every poster in the thread, and especially DVap. The vinegar solution was a no brainer. Also because I had mixed feelings handling the 37%, or so, sulfuric acid. I really think that solution (pun intended) should be widely known.

Case colsed.

 

[DVap]

One of the sayings in chemistry, "When in doubt, throw it out".

White vinegar is one of those things you can generally take to the bank as far as the labeling... and everybody agrees as to what 5% actually means. Add to this the fact that it's so safe as to be edible and you have a winner.

 

[DVap]

Trying to unconfuse myself now, but I think I get what DVap is saying is that componenent percentages given in the MSDS are either wt/vol or arbitrary numbers. The question is the same as priestie is asking...



For some reason, that looks correct to me, and I wouldve plugged in the density of the 37% solution converted to litres in there as well (1.28*1000).

And when you find yourself with more questions than answers, you should see that as a strong suggestion that you should be barking up another tree. This stuff is really simple. If you find its been made complicated, then refer to comment about barking up another tree.

 

[priestie]

One of the sayings in chemistry, "When in doubt, throw it out".

White vinegar is one of those things you can generally take to the bank as far as the labeling... and everybody agrees as to what 5% actually means. Add to this the fact that it's so safe as to be edible and you have a winner.

I really don't understand why anyone would use HCL or H2SO4, when you can use vinegar. But, mixing the titrant yourself adds another level of uncertainty, which could be why.

Thanks again DVap.

 

[MarkyD]

Thanks for all your great work DVap.