Another Question...

Hi
You guys helped me before but I need one more thing... I have Trichloroacetic Acid, 100g. I need to dilute it with distilled water to a 30% strength. I guess I am looking for specific instructions on how much to mix of each to get this strength. The reason I ask is I thought the answer would be to add 70% distilled water to the 100g of TCA and that would equal 30% strength solution. But as I know NOTHING about chemistry and my husband thinks he knows everything I should ask for outside help. He is saying there is more to it than that. He is using some formulation where he uses the h2o density, TCA density coming to a final result of
2.1 oz tca + 7.9 oz h2o= 10.0 total oz of 30% strength


Can someone tell me can I trust his figures? lol How many ounces of water to add to 100g of TCA for a 30% strength.
Thank You

Well you should use molar weigth to calculate this.
Here how:
TrichloroAcetic Acid is CCl₃COOH so
2 C atoms @ 12^g/_mol
3 Cl atoms @ 35^g/_mol
2 O atoms @
16^g/_mol
and 1 H atom @ 1^g/_mol
Here the calcul:
(2*12)+(3*35)+(2*16)+(1*1)=161^g/_mol

So you have TCA @ 161^g/_mol and you have 100g of it thus 100g/161^g/_mol=0.621mol of it

Pure Water is
2 H atoms @ 1^g/_mol
and 1 O atom @ 16^g/_mol
Here the calcul:
(2*1)+(1*16)=18^g/_mol

You need 30mol of TCA by 100mol of water or a ³/₁₀ ratio since you only have 0.621mol of TCA and you need 3.33 more Water (³/₁₀^-1 so:
0.621*3.33=2.07mol of water
2.07mol*18^g/_mol=37.26g

So you need to mix 37.26g of water, rounded up to 38g, which is 38ml

PS: you might like to get a second advice just to be sure that i'm not all fucked up

[Edited on 2-2-2004 by Blind Angel]

I try to say when your dealing with liquids try to use liquid units of measurements. Grams for solids, milliliters for liquids. What your asking is a simple elementry math problem. If you got 100ml of a mixed solution, 70ml TCA and 30ml water, than 70% of your solution is TCA. When all else fails find a density table for water and TCA, then weight it out on a digital scale and you will know your concetration . I think all these other geniuses around here are a little to over qualified to answer this question.





[Edited on 2-2-2004 by tom haggen]

Just don't look at him directly in the eyes, he may get agressive

lol

Third degree burns: A gift they'll never forget...

ROFL
I am glad this is in the beginnings section... let's just hope that 'beginners' dont try it for themselves
You look very pretty I_am_a_fish

For a more personnal enlightment, i would like to know if my calculs were accurate....

BlindAngel, you calculated mole-percent. The calculation is certainly correct BUT I doubt it is what you find in reality. The unit mole percent is used in chemistry mainly, but not household products.
Anyway, I should think that mixing 30 g of TCA and 70 g of H2O should be fine. Gives a 30% solution. Or 30 ml TCA and 70 ml H2O. This time its per volume. You need to find out which of the two it is, then we can tell. But I am quite certain it wouldnt be mole percent. I.e. if you have a 34% solution of HCl (which is pretty damn strong and fuming), it doesn't mean 34 ml HCl and 66 ml H2O, as HCl is a gas anyhow. So, clearly in that case it means, 1 kilogram of 34 % HCl solution will contain 340 g HCl and 660 grams of H2O. That DOESN'T mean that a kg of this is equal to 1 liter, as this depends on the density of the solution.
Did that help?
Anyway, tnheygirl, just find out whether its weight per volume or weight per weight or volume per volume etc

There is some confusion here.

And its a common problem. The labelling in consumer products is often unclear at best.

How does the company use the expression %.

Are they referring to Mass Percent, Volume Percent, a mixed percent, or some other more obscure calculation? Perhaps they are calculating the mass percent as straight mass, molar mass, molal mass.....

The fact is companies can be pretty obfusticating. And yes I mean that literally. It is to the companies benefit to express the percent composition in a way that makes the retail consumer feel that they are getting their money's worth.

Basically, you will really have to know the method the company uses to calculate their percentages.

If you don't, you run the risk of having a product that is vastly weaker or vastly stronger than the product you are trying to copy.

You see....percent is just "per" and "cent"
or
"of" and "one hundred"

You really need to contact the company whose percentages you are quoting to see how they calculate percentage. And be prepared to end up talking to some middleaged woman with her grade ten, who's job is just to tell you how to open the bottle/jar, not to put it into your mouth and other miscellaneous things like that.

That kind of person might give you a faulty but reasonable sounding answer. I bet they don't get your kind of question much and if they did, they would just assume that percent means straight mass percent like most other people who don't even know about any other kind.

The problem with that is, that the people who labeled the bottle were scientists and we use all sorts of "wacky" weights and measures for the sake of consistency and accuracy, and reproducibility.

For instance most people don't even realise that 100 mil's of water at room temperature is lighter and contains less molecules than 100 mil's of cold water.....its not a big deal if you're thirsty but if you are performing a chemical reaction....

and that different chemicals expand and contract with different rates in temperature and pressure.

SO....if there were temperature fluctuations in the factory, the percent composition of the product would change.

And it would be very bad to have a product get stronger in winter and weaker in summer (or vise versa)wouldn't it!!!

This and other assorted inconsistencies make scientists use very different units of measure than everybody else.

so If I had to guess I'd say the logical thing to do would be to use mass percent on the factory floor.

But companies do some strangely illogical things sometimes.


You'd really have to get in touch with somebody in the research and development department. Then you'd stand a better chance of talking to someone who really knows what they are talking about. In which case they would be really curious about WHY you wanted to know.

Good Luck.

Wow, an engineer using the measurement of ounces ... do you measure the size of a transistor in chips in inches?
Rofl - the density of water is 29.6 g/oz - never heard that one before. Thanks for cheering up my day

Anyway, what you have done is measuring the percentage by weight. How do you know it is not by volumne? I.e. 100 ml of TCA and 233.3 ml of H2O? in this case the concentration would be higher, due to the high density of TCA. Lol, who knows, maybe it won't work in this case as the conc. is too low the way you want to do it
Good luck anyhow.

PS I'd rather have a questioning stubborn wife than a boring accepting one!

a rod of furlongs to Tipperary!

Really too bad those photo's were removed. It's interesting to see what a woman will do to herself....

it's as good a deterrent as I've ever seen to DIY cosmetics.

Also....to engineering husband. We all hope your assumptions(straight mass percent) regarding the units you used in your calculations are correct.

If she wakes up with a face that looks like poached salmon. REDUCE CONCENTRATION.

Seems like quite a gamble to avoid a phone call to the R&D dept of a cosmetics firm.

But Hey! I do so admire reckless courage and wanton abandon.

lol
Density of water is approx 62.4lb/cf
Converted mass: lbs to grams, and volume: cubic feet to ounces. Using those conversions found water to be 29.6grams/oz This is just a different way to describe the density of water.

TCA was purchased by mass, 100g not 100ml so we are using weight

HA Try living with a stubborn woman! WHat can I say she is a rebel...

HI ITS me again TNheygirl

I have decided after all the posts freaking out about this and too many different calculations, that I will not be performing any acid peels at home! I'm sending the stuff back! Thank You all for replying to my posts! TN

Congratulations!.....tsk!....tsk!.....

All you amateur scientists freaking out the poor lady.....

and for what.....just trying to do a controlled chemical burn on her own face......

Every red-blooded american girl wants her facial skin coming off in sheets.....

there is nothing prettier than that.......is there?

you should be ashamed of yourselves

crazy internet geeks!

p.s. yessir Mr. Engineer. water does weigh about an ounce per ounce and a gram per cc/ml (at standard temperature and pressure)....

waitasecond!!!

Is that a coincidence or what!?!.....

P.S.(seriously though.) I'm glad we could help. I'd still be careful with the store bought stuff. It would be wise to be near a tub of water when using it and not to use it alone. If you were to get some into your eyes, the gelling agents would make it somewhat difficult to get out. If you have ever broken your nose or been burned in the eye by someones stray ciggarette at a party, you know how disorienting pain can be. (and you don't want to go blind)

And what pics would those be?

Quote:

Originally posted by Hermes_Trismegistus But Hey! I do so admire reckless courage and wanton abandon.