NaOH equivalency

[Stuart Spigel]

Any info on the equivalency of a liquid NaOH drain opener with crystalline NaOH. The bottle gives no indication of concentration. I doubt that there would be much variability between brands, however.

Thanks.

 

[Anon Ymous]

Hmmmm, perhaps you could check it's density and consult some table online? Even so, I don't find it a particularly good idea to use it for photographic purposes.

 

[Stuart Spigel]

Hmmmm, perhaps you could check it's density and consult some table online? Even so, I don't find it a particularly good idea to use it for photographic purposes.

...because of the uncertainty factor re: its concentration?

 

[Anon Ymous]

...because of the uncertainty factor re: its concentration?

You don't necessarily know what else is in there.
You can't be very sure about it's concentration.
This solution will likely absorb carbon dioxide from the atmosphere and partially convert to sodium carbonate. This may, or may not be a problem.
NaOH is a cheap compound that can easily be bought pure.

And finally, if you'd like to make a very concentrated film developer, potassium carbonate is a very soluble alkali that can be used in a two part developer, just like Pyrocat HD and it's variants. Of course, that's just my opinion.

 

[RauschenOderKorn]

That might be an issue, but I would worry more about purity or impurity. What you get in the supermarket here is quite often coloured, maybe has some scent, something to avoid critalization even at lower temps and the NaOH use for producing the drain cleaner maybe is not A++ quality.

But to answer your initial question: you can try measuring the ph of your particular product and look up the corresponding concentration.

 

[Anon Ymous]

...But to answer your initial question: you can try measuring the ph of your particular product and look up the corresponding concentration.

I don't think it's that simple. Even a low concentration solution will have a very high pH, making it hard to measure.

 

[darkroommike]

Some liquid drain openers are acid, no NaOH at all. Some contain bleach and sodium hydroxide. Drano crystal is pretty much just lye but some others include aluminum flake and wetting agents. [edit] Drano has aluminum. "Ingredients: Sodium Hydroxide, Aluminum Chips, Sodium Nitrate, Sodium Chloride, Sun Chemical Pigment Green 7"

 

[Photo Engineer]

I would not use it. That variety of NaOH is very impure to start with. Some I have seen are gray or brown.

PE

 

[Stuart Spigel]

Thanks to all for the input. The product in question is liquid, not solid, and contains only NaOH.

 

[Photo Engineer]

Stuart, I've seen many such products. As long as they are reasonably pure for the intended purpose, then they deem it OK. We really need to use Photograde chemicals!

PE

 

[Gerald C Koch]

Drain cleaners often contain other chemicals. In addition sodium hydroxide absorbs carbon dioxide from the are and loses potency to become sodium carbonate. Check the MSDS for the product. But I would really recommend using solid sodium hydroxide. Something like Red Devil lye can be used for photographic purposes. I use it all the time without problems.

 

[Patrick Robert James]

I've used Roebic Crystal drain cleaner successfully. Easier than mail order. Just have to pop over to Lowe's. It is supposed to be 100% Sodium Hydroxide and nothing else.

 

[RauschenOderKorn]

I don't think it's that simple. Even a low concentration solution will have a very high pH, making it hard to measure.

Yes, it would require a ph meter. But if you go by density, you´d have to know the exact composition (not just MSDS data with dangerous substances).

I still would not recommend using drain cleaner, photo quality sodium hydroxide is not that expensive. (In any case, it will be cheaper than a good ph meter )

 

[Gerald C Koch]

Yes, it would require a ph meter. But if you go by density, you´d have to know the exact composition (not just MSDS data with dangerous substances).

I still would not recommend using drain cleaner, photo quality sodium hydroxide is not that expensive. (In any case, it will be cheaper than a good ph meter )

At high pH values pH meters are not very accurate. Same applies to very acid solutions. At least one form of crystalline drain cleaner contains aluminum turnings to create a churning effect. Again an unwanted addition.

 

[Anon Ymous]

At high pH values pH meters are not very accurate. Same applies to very acid solutions...

Yes, that's what I alluded to in my previous post. This whole pH measurement thing is quite a mess IMHO.

 

[Photo Engineer]

It isn't a mess if you know what is going on. There are tables for the offsets needed to correct. However, only a few photographic solutions need pure NaOH or KOH.

PE

 

[Anon Ymous]

It isn't a mess if you know what is going on. There are tables for the offsets needed to correct...

Perhaps these tables are provided by the pH meter's manufacturer? In any case, the average hobbyist doesn't have a high end meter, but only something cheap. Can such a meter be used for measuring a pH above 14?

 

[RauschenOderKorn]

Perhaps these tables are provided by the pH meter's manufacturer? In any case, the average hobbyist doesn't have a high end meter, but only something cheap. Can such a meter be used for measuring a pH above 14?

I´d take a small sample of the original liquid / gel and dillute it with a controlled amount of destilled water until reasonable measurement is possible.

 

[Anon Ymous]

I´d take a small sample of the original liquid / gel and dillute it with a controlled amount of destilled water until reasonable measurement is possible.

Dilute to 100 times final volume and add 2 to pH value for example?

 

[RauschenOderKorn]

I have not tried this, so I hope I am not writing something stupid. But I was thinking along the following lines:

Example: concentrate is dilluted to 1% (1+99) and gives a pH of 13,00 -> diluted solution has a concentration of 0,1 mol / l or 3,9997 g/l -> so the undiluted solution was 100x stronger equaling 10 mol/l or 399,97 g/l

 

[Gerald C Koch]

Perhaps these tables are provided by the pH meter's manufacturer? In any case, the average hobbyist doesn't have a high end meter, but only something cheap. Can such a meter be used for measuring a pH above 14?

The are no pH values above 14 for an aqueous solutions. This is due to what is called The Limiting Effect. The solvent, in this case, water limits the maximum pH. You can get more alkaline solutions by switching solvents say to liquid ammonia.

 

[Photo Engineer]

As Jerry said above, there is no pH above 14 and I'll add that there is none below 1. If you are working above 11 or below 4, you are not doing photography, you are dissolving gelatin or some such. The only processes at 14 are instant, as they often use molar KOH or NaOH in the goo. At 11, most pH meters are quite accurate, and really if you are repeatable with such a meter you are OK.

PE

 

[Gerald C Koch]

In my post #21 I meant to say 'Leveling Effect' and not limiting effect. Zee leetle gray cells were occupied elsewhere.

In an aqueous solution the strongest base is the hydroxide ion and the strongest acid is the hydrogen ion. If a stronger base should be added then it would react with water molecules and release hydroxide ions. Therefore you cannot get a stronger base. The solvent water levels the effect. In liquid ammonia the strongest base is the amide ion NH2- and the strongest acid is the hydrogen ion.

 

[Anon Ymous]

As Jerry said above, there is no pH above 14 and I'll add that there is none below 1.

Ok, I'm honestly puzzled. A 10% solution of NaOH is not particularly concentrated and it's a 2,5M solution. In theory at least, it should be above pH 14, shouldn't it? Is 14 really a hard limit?

If you are working above 11 or below 4, you are not doing photography, you are dissolving gelatin or some such. The only processes at 14 are instant, as they often use molar KOH or NaOH in the goo.

For the most part, I agree, with the exception of E6 CD that goes up to pH 12.

At 11, most pH meters are quite accurate, and really if you are repeatable with such a meter you are OK.

PE

Any problems I had have been at about the pH ~12 point and above. I got readings that were off, some moderately, some way off. That said, I'm not entirely sure that all of my chemicals are as pure as they should.

 

[Photo Engineer]

Values for pH extend from 1 to 14 with 7 being neutral. This is a hard limit. It represents the negative log of the hydrogen ion concentration. There is a corresponding pOH scale that we can forget about here, as well as pAg and others that anyone can create an electrode for. The values are all represented as being aqueous or water based. You can get other scales such as in liquid ammonia which are much more alkaline, and can burst into flame in air...

So, sticking with water we have 1 to 14 and that is it. Error increases about about 11 and below about 3 but if you do things repeatably, even that should not matter.

PE