solution %

[Lenin]

Usually, an x% solution means a solution of x g per 100 mL water.

[hypo]

it means the answer is in the utfse, a quadrillion times.
(lenin is wrong: it's per weight)

[Lenin]

And what is the weight of 100 ml water?   

[Bandil]

UTFCN¹!!!!!

100 mL water = 100 g's water... How are you even able to order a happy meal with those kinds of questions at hand?

Regards
Bandil

[1]
UTFCN = Use The Fucking CyaNide... Meaning that the question is so lame that a UTFSE would be inapropriate  

[hypo]

but 50g x in 100g water is 50g in 150g of solution, giving
a 33.3% solution, not 50% as your posting implied.
elementary school math.  

[armageddon]

Usually the strength of acids is measured in "percent weight/volume", meaning 100ml HCl with a concentration of  36.46% contains 36.46 grams (or 1 mol) HCl (for example).

But it depends on the manufacturer I think, mine is always w/v though...

Greetz A

[hypo]

and tell your manufacturer to use scientific measurements (mol/l or mass%),
not some furlong per hogshead-yank craziness. the rule says that % without
further indication is mass%.

[armageddon]

w/v is almost the same like mol/liter: you just have to know the molar weight! Does this necessarity mean that it is unscientific??

And for mass percent, you don't have to know only the weight of the dissolved compound, but also the density of its solution to be able to calculate anything...

IMO the measurement of my manufacturer is quite useable in a scientific sense: you know the volume of the solution, you know the weight of the dissolved compound, and in most cases, you would like to measure out a certain molar amount: just measure out a certain volume and be happy because it contains xx grams of the desired compound.

What's difficult or unscientific about that??

A

[hypo]

> w/v is almost the same like mol/liter

yeah, great. then why not directly state mol/l (M)?
honestly: have you _ever_ cared about how many g HCl there is in some defined volume?
and if you really need that, then call it what it is: g/ml

> What's difficult or unscientific about that??

it's not difficult, but it's stupid!
look: a percentage means parts per hundred (parts). parts mass per parts volume
does not make sense, because mass and volume are different. if you have a mass%, then
it's irrelevant if you compute in g, kg, ounces or truckloads. with %(w/v) you're not
unit independent anymore, which kind of totally defeats the purpose of giving a percentage.
it's just _totally_ wrong.

and apart from that: % without further indication is mass%, so if your supplier says
36% and it's not mass%, then he's giving a wrong measurement. period. it's like when
someone sells you 10g of hash and only gives you 9g, because he's using some different
definition of g. duh.

[armageddon]

if you really need that, then call it what it is: g/ml ...which is exactly w/v! Or not?
(I hope you don't criticize me because you're jealous about my "w/v" supplier?   )

Something like "dissolve xx grams NaOH in xx ml water and dilute this to 100ml with more water" results in a solution whose concentration is given as grams/liter, a.k.a. w/v...

- and this is a common technique for making solutions with a certain concentration, at least where I come from...

And w/v just means x weight parts per 100 volume parts - parts is just a variable number and tells about the proportions of numbers. Although it is usually meant as parts per weight of course - but not if stated as being w/v.

It is not stupid, but recalculated to allow for easier measurements (volumes of liquids are easier to measure than weight or density).

If the concentration is given in percent w/w, you will have to weigh your solution to determine its concentration, or you'll have to look up table with different densities at different concentrations and then measure the density of your soln. with an areometer...

...maybe my manufacturer has done either of these himself before labelling his acid bottles, and I don't have to weigh or check density anymore???

(perhaps my hash dealer sells portions that are worth a certain amount of money - rather than pieces with defined weight - but still his price is cash per weight. Only that he has recalculated it to make for easier measurement just like "xx grams for 100 bucks", and I have to recalculate back to know if I got cheated.. He just does so because this kind of measurement makes it easier for him - he doesn't have to change any money, he just has to weigh his hash.   )

A

[hypo]

you could have spared yourself the post, because it did not address what i said.

> And w/v just means x weight parts per 100 volume parts

and that my dear is madness. it doesn't make sense (how much is one weight part
in volumes?)

i don't object giving g/ml, i object:
a) calling it a percentage because that's nonsense
b) calling it % without the indication of (w/v) because % means mass%. <- (big period)

[armageddon]

I see. I will try to get my manufacturer to change his definition methods because some other hive member marked it being madness to state a concentration as weight per volume.........

but I think I will stockpile lots of their old bottles before doing so; cuz I can live very well with this "nonsense", at least better than with weighing any solution I want to use...

Last example for anyone who is as "unlucky" as I am and has lying around any acid, with a strenght given in weight/volume:

    33% w/v -> 33 percent of the amount of solution is the amount of the dissolved compound in weight, meaning 1000(ml) contain 330(g) - and 1 part is therefore 1g or 1ml, depending on what is meant - it just tells about the relations of plain numbers, not about the relations between the units they stand for...

   100 parts  * volume  = 33  parts  * weight   |  / 10
    10 parts (* volume) = 3.3 parts (* weight)
    10 (ml)             = 3.3 (g)

scientific enough? Only disadvantage is that you have to check the density for being able to calculate how much solvent 10ml contain:

10(ml) * X (density g/ml) - 3.3(g) = Y(g)
Y(g) * Z (density of solvent) = Y2(ml)  <-- volume of remaining solvent contained in 10ml of a 33% w/v solution


And I still don't know why I learned time ago that solutions with a certain concentration are made by dissolving the compound in a small amount of solvent and then diluting to a certain volume!?! Any ideas on why universities consider it the right thing to teach their students how to make w/v solutions??

A

[hypo]

dude, you're not addressing what i'm saying. not at all.
did you get the part where i said g/l is ok? so why are you arguing about that?

> 1g or 1ml, depending on what is meant

but with solutions 1g does NOT correspond to 1ml. so they are NOT interchangeable.

> it just tells about the relations of plain numbers, not about the relations between
> the units they stand for...

plain numbers are NOT scientific. what are you talking about oranges? apples?

> scientific enough?

no. STUPID. if you use units, then specify them, god dammit.

you know, on planet X they might not be using grams and ml, so what are they going
to do with %(w/v)? on the other hand %(v/v) or %(w/w) is INDEPENDANT of units, that's
what percentages are for. if you don't get that, go back to elementary school.

[armageddon]

> And w/v just means x weight parts per 100 volume parts
and that my dear is madness. it doesn't make sense (how much is one weight part in volumes?)



That's mainly your opinion, so please stop criticizing me. W/v measurement may be not absolutely accurate scientific math - but it is pretty usable when working in the lab, and there's no need for you to flame me because I mention that "w/v" measurement of acid concentrations also has its advantages!!

I never did claim "weight/weight" being madness nor not useable, although you can't conclude directly how much of the dissolved compound a certain volume contains; I think the point was to help someone having difficulties with determining any concentration, and with the info you and me gave, the problem is reduced to the question "is it w/v or w/w?" - there's no need to convince anybee about any method of measurement being bullshit! And even if it was: there are manufacturers using w/v labelling, so I don't see why you try to convince me about it being bullshit - as long as there are chemicals labelled with w/v concentrations, explaining how to work with it makes pretty much sense to me..

Ever heard of constructive criticizm? Just because you can't stand w/v concentrations doesn't mean you have the right of telling me I'm an idiot and/or not able of doing scientific measurements...

on planet X (..) ...there may be some different gravity, meaning different density - and suddenly your measurement becomes unreliable, as both are based on solutions having a certain density at certain concentrations - duh...

A

[hypo]

> but it is pretty usable when working in the lab

then why don't you call it what it is: g/l. isn't that hard, is it?

> the problem is reduced to the question "is it w/v or w/w?

as i stated about a myriad of times now: % implies (w/w).
if its (v/v) or (w/v), then it must be stated so.

> Just because you can't stand w/v concentrations doesn't mean you have the
> right of telling me I'm an idiot and/or not able of doing scientific measurements...

i didn't say that you are idiotic, but the percentage (w/v) is.

[armageddon]

then why don't you call it what it is: g/l. isn't that hard, is it?

Yeah, I'll call it what it is:

certain weight per certain amount of volume - A.K.A. W/V...


as i stated about a myriad of times now: % implies (w/w).
if its (v/v) or (w/v), then it must be stated so.

I never questioned that - I just mentioned that my mineral acid supplier gives a concentration of w/v, and explained how to work with it.

(sigh too)

I mean: C'mon, it wasn't ME who invented the weight/volume thing - it has been common knowledge for the last century that there are w/w, w/v and v/v concentrations (just look up any chemical dictionary for abbreviations!)...

A

[hypo]

you are talking about _concentrations_, while this thread is about _percentages_.

and excuse me, but giving a (w/v) _percentage_ is wrong. that's not a percentage
at all. call it degrees or whatever, but not %. the chemist who invented that probably
inhaled to much of solvents during labwork.

> I just mentioned that my mineral acid supplier gives a concentration of w/v,

but he states so and thus there is not question what it is (well, actually you
don't know whether it's g/100ml or lbs/liquid ounce). the original poster
asked what it is when there is no further indication.

[armageddon]

You're right.

[armageddon]

Dissolving 40 grams NaOH in d.H₂O and diluting it to 1000ml results in a 1M solution.

This solution contains 4 grams NaOH w/v.

With a concentration given in weight/volume, you are able to tell directly from the volume about how much NaOH (in grams) you have.

If you want to know about the *real* percentage of NaOH/water solutions (v/v, as solutions are liquids and usually being measured in volume rather than weight), you have to calculate from the weight of dissolved NaOH;
calculate the density of a saturated NaOH solution gotten from the amount of NaOH, then look up its density, then you know the volume of your saturated solution containing 40 grams; and THEN you can calculate how much additional water you have in there and calculate then the total percentage of NaOH present.

With a concentration given as percentage of weight (w/w), you will have to weigh each and every solution for knowing how much NaOH {or anything else} you have in there; or you'll have to learn the density for each concentration at a certain tempertaure by heart.. But it is mathematically correct like nothing else!

.PERIOD.

[hypo]

you know, if you like we can continue stating the same thing again
and again.... (hey, i'm getting paid for it, so no problem for me...)

look: there is nothing wrong with giving a concentration as mass per volume
(eg. g/l). but it's wrong to call it a percentage.

i'm well aware of the advantages of giving mass/volume (easy to measure) or
mass/mass (independant of temperature (save relativistic effects   )).
you don't have to repeat that every time.

but don't call it percentage, when it isn't, ok?

at your university, do they really say "i made a 40% solution", when they diluted
40g NaOH to 100ml? that's wrong!

[armageddon]

I see, w/v isn't a real *percentage* in the mathematical sense but rather a (nevertheless useful) *unit* for concentrations of solutions consisting of dissolved (solid) substances. Therefore my "w/v" post didn't exactly answer the question of this thread ("what does % mean?").

I just wasn't happy with your suggestion to change my supplier because of "unscientific measurement/labelling"...

A

[hypo]

the whole absurdity of stating a %(w/v) should become clear when
you give the %age of a concentrated H2SO4 solution: it has 180%!
what the heck is a 180% solution!? is there more in the solution
than the solution itself!? if i ever make such a thing i know what
to do: drop it and run as fast as i can out of fear that if colapses
into a singularity and opens a worm hole... i mean having a few ml of
physical impossibility can not be healthy....  

and while we're at it, %(v/v) sucks too for everything but perfect
gases or liquids: with what volume are you working, the volume of
the pure isolated substance or the effective volume inside the
solution? i think i'll write a nastygramm to my beer supplier...

[r2e3]

chemists......

still vex the hell out of me..    

why not maths god???