Mixing chemical question

[mark]

When something says mix up a 10% solution of X how do I do that? Ratios I can handle. % solutions have me completely bamboozled. I have been looking on the net and my head is starting to hurt.

I need a layman's explanation.

 

[Ian Grant]

10% is 100gm per litre, dead easy.

Ian

 

[Robert Hall]

10% is 100gm per litre, dead easy.

Ian

But be careful that some chems take up more room in the liter than others. Starting with 1 liter then adding chems does not a correct percentage make.

And you don't want to add water to some chems such as acid as it may spit or explode acid everywhere.

Start with a portion of the water, maybe 75%, then add the chems, then top it off to a liter.

Cheers,

 

[Kami-the-Trout]

10% is 100gm per litre, dead easy.

Ian

Or 10 grams per 100 ml, or one gram per 10 ml . . . it's all 10 per cent.

 

[mark]

Now why couldn't those sites say that. Damn. Thanks.

 

[olleorama]

Percent can be either by volume or by weight. Be careful on what properties are used.

 

[Ian Grant]

Percent can be either by volume or by weight. Be careful on what properties are used.

Or they can be a mix of both

Ian

 

[Photo Engineer]

If you add 10 grams of Sodium Chloride to 80 ml of water and then dilute to 100 ml, you have a 10% wt/vol solution.

If you add 10 ml of Alcohol to 80 ml of water and then dilute to 100 ml with water, you have a 10% vol/vol solution.

If you add 10 grams of alcohol to 80 grams of water and then dilute to 100 grams, you have a 10% wt/wt solution.

If you add 10 ml of Alcohol to 80 grams of water and then dilute to 100 grams you have a 10% vol/wt solutoin.

Note that you can add water to make 100 grams or 100 ml. This gives a different solution in each case.

Each is different. Each will be almost the same but not quite. If you use the same method every time, it will at least be consistent.

I use wt/wt for viscous materials or in the dark as weight is easier to manage in these cases. I use wt / vol for solid-liquid and I use vol/vol for two liquids which are non viscous and when I am not dark as combinations of this sort are pretty much standard.

PE

 

[mark]

I need to make a 9% solution of silver nitrate. Since it is a powder do I do wt/vol? Head ache is back.

 

[Photo Engineer]

Do wt/vol.

PE

 

[nick mulder]

What is it called when you use an amount of discrete molecules / amount of discrete molecules ratio ?

I would have thought this would be the best approach considering the actual activity is on a molecule to molecule basis - once you knew the reactions things like capacity would become easier to understand for instance

 

[Photo Engineer]

Depending on compounds used it can be called Molar or Normal. A Molar solution contains 6.023 x 10^23 molecules (the Avogadro number) of the substance in question and an amount of solvent atoms that can be calculated using the Avogadro number applied to the quantity of the solvent.

That is, if I understood your question correctly.

Going on then, one mole of Sodium Hydroxide made up to 1 liter with water can react exactly 1:1 with 1 mole of Hydrochloric acid made up to 1 liter with water. This is because they react 1:1 and you have exactly 1 mole of each substance.

PE

 

[nick mulder]

Depending on compounds used it can be called Molar or Normal. A Molar solution contains 6.023 x 10^23 molecules (the Avogadro number) of the substance in question and an amount of solvent atoms that can be calculated using the Avogadro number applied to the quantity of the solvent.

That is, if I understood your question correctly.

Going on then, one mole of Sodium Hydroxide made up to 1 liter with water can react exactly 1:1 with 1 mole of Hydrochloric acid made up to 1 liter with water. This is because they react 1:1 and you have exactly 1 mole of each substance.

PE

Yup, you understood my question ... Ok Molar or normal.

Seems like a more accurate way to go about things, but I guess with the added complication of having to learn or know how things react to find how the ratio will work and then the weight or volume to molar amount facts and figures - but what's a little chemistry amongst analog photographers

 

[mark]

This is exactly why I had a head ache. I jus wanna take pichers

 

[Photo Engineer]

If you just want to take pitchers then use prepared chemicals and don't scratch mix your own. That way you do not have to deal with chemistry, percents and other annoying chemical trivia which are not really needed to be a good photographer.

PE

 

[nick mulder]

If you just want to take pitchers then use prepared chemicals and don't scratch mix your own. That way you do not have to deal with chemistry, percents and other annoying chemical trivia which are not really needed to be a good photographer.

PE

When I started photography it was all about the shoot - processing simply done at the lab and the output was taken for granted that what I got was what I got... The more I read up and get into printing (alt) the more and more it fascinates me - at the moment I'm finding it hard to rectify the word 'photographer' with the printing process - printing has such huge variable capability it's really merely an associated practice done by 'printers'...

Well, that's what I'm trying on for size anyway - we'll see how far I get with it

 

[Photo Engineer]

Nick, you are absolutely right. But, then you have to learn some elements (pun alert) of chemistry.

I am merely trying to clarify the two and mention the alternatives.

PE

 

[Loris Medici]

Actually the chemistry knowledge you need for photographic work (unless you're formulating something new or take something and try to improve it and/or adapt to your special needs) is pretty simple - Chemistry 101 level. I'm very comfortable with my 20 y/o high school chemistry knowledge (and I have done nothing to improve it during all that time...), do alt-processes, mix my own developer, compound something I need from something else I've already got on hands... Maybe it's something related to the difference between the American and Turkish education systems, I don't know.

Regards,
Loris.

 

[Photo Engineer]

Chemistry education (and Physics as well) is in a rather sad state here I think. Not like it was when I took it. It seems like people are afraid of Chemistry and kind of afraid of the sciences in general.

PE

 

[Akki14]

I quite liked Chemistry in high school in the US about 13 years ago now. Didn't seem too bad. I have to admit mixing photo chemicals for alt processes is easier than high school chemistry class... Don't have to write up lab reports afterwards either.

 

[Loris Medici]

Indeed, the most complex alt-process mixing I can think of is New Cyanotype or Argyrotype. (And that's w/o having silver(I) oxide on hands...) And both are pretty easily accomplished.

Depends on which school you've attended + your personal interest to the subject then...

Regards,
Loris.

I quite liked Chemistry in high school in the US about 13 years ago now. Didn't seem too bad. I have to admit mixing photo chemicals for alt processes is easier than high school chemistry class... Don't have to write up lab reports afterwards either.

 

[Photo Engineer]

I think that today, the schools are more interested in protecting the students from any potential injury in chem lab than they are in teaching and more interested in sports than in science.

PE

 

[CBG]

Plus the students and almost everyone else in society are told that "chemicals" are dangerous. Thus people are terrified of stop bath after they enjoy their health salad.

 

[mpirie]

... Don't have to write up lab reports afterwards either.

When it comes to alternative photographic processes your "lab report" finds a much bigger (and some might say more appreciative ) audience on this forum

My difficulty when it comes to mixing chemical solutions was the conundrum we faced in first grade chemistry class where we took 50ml of methylated spirit and 50ml of water then had to explain why the combined solution only added up to 95ml.

Of course i know now that it's molecular size, but I wonder sometimes if this is taken into account in mixing instructions, or whether the differences are negligible?

Mike

 

[Photo Engineer]

Mike;

Sorry to burst your bubble but it is not molecular size that causes the "shrinkage".

And yes it is taken into consideration. In my above description, it is the reason why one must specify what the combined units are (wt/wt, wt/vol, vol/wt etc.)...

PE