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Photo Forum / Film Photography / Darkroom / January 2006NaOH question
I've forgotten enough of my high school chemistry so tha I don't understand Anchell's statement in one of the Cookbooks that a solution of NaOH and water will have a short shelf life. Can anyone explain this? I have a half filled, gallon jug of 50% that I use for a variety of purposes. Is it time to throw this away? -Lew > I've forgotten enough of my high school chemistry so tha I don't understand > Anchell's statement in one of the Cookbooks that a solution of NaOH and [quoted text clipped - 4 lines] > > -Lew Now you know what the PH meter is for :) I would think though perhaps I am wrong that by simply measuring the water content and adjusting by adding additional distilled one as needed could maintain the PH. I am going to email this to Steve, if he isn't too grumpy he might answer :)  Signature"To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public."--Theodore Roosevelt, May 7, 1918 greg_____photo(dot)com > I've forgotten enough of my high school chemistry so tha I don't understand > Anchell's statement in one of the Cookbooks that a solution of NaOH and > water will have a short shelf life. Can anyone explain this? > > I have a half filled, gallon jug of 50% that I use for a variety of > purposes. Is it time to throw this away? It should be fine. Dilute NaOH solutions absorb carbon dioxide from the atmosphere forming carbonic acid which is converted to sodium carbonate in a NaOH solution, neutralizing a small amount of NaOH. Carbonate is insoluble in a 40-50% NaOH solution so the reaction is insignificant, and the solution has a long storage life. In labs, NaOH is commonly used as a 50% w/w solution since it is more stable than pellets, crystals or dilute solutions. hydroxides (sodium, potassium, lithium etc) absorb carbon dioxide from the air. It beans you have less hydroxides but more carbonates. In practical terms, it equals less alkalinity, less developer strength, lower pH. However it takes a lot of time. It takes many many years to make 20% KOH solution (electrolyte) of NiFe battery unsuitable for service due to CO2 absorbtion. If your 50% NaOH is kept in a well closed bottle, then it should last years. Store in a glass (hard glass), 50% hydroxides dissolve slowly glass forming silicates. Plastic is safer, but all plastics permeate carbon dioxide (very slowly). Do not measure pH unless you are ready to pay for a new electrode. Most electrodes are marked as up to pH14, but it does affect the sensing bulb. You would need to resuscitate in diluted HCl to get the membrane right. #I've forgotten enough of my high school chemistry so tha I don't understand #Anchell's statement in one of the Cookbooks that a solution of NaOH and #water will have a short shelf life. Can anyone explain this? # # I have a half filled, gallon jug of 50% that I use for a variety of #purposes. Is it time to throw this away? # #-Lew # >hydroxides (sodium, potassium, lithium etc) absorb carbon dioxide from >the air. It beans you have less hydroxides but more carbonates. In [quoted text clipped - 23 lines] ># > It may be of additional interest to know that it is not difficult to determine the strength of a sodium or potassium hydroxide solution, either in weight percent or weight per unit volume. Weigh a volume of the solution measured at 20 C (68 F). Divide the weight by the volume to get the specific gravity. Find in the CRC Handbook of Chemistry and Physics the section that has tables called "CONCENTRATIVE PROPERTIES OF AQUEOUS SOLUTIONS". Suppose you weigh 100 ml of a sodium hydroxide solution and find it weighs 128.7 grams at 20 C. The weight percent of that solution is 26% or 26 grams of sodium hydroxide per 100 grams of solution. 1 liter contains 334 grams at 20 C. These numbers are in the table. In cases where high precicion is necessary, it will be better to weigh out the amount you need, as the weight percentage does not vary with temperature..The weight percentage as well as the weight per unit volume can change due to aeration which precipitates some carbonate, but this method uses only what remains dissolved, so it shold be a good way to keep track of the strength. > > > Anchell's statement ... a solution of NaOH > > > and water will have a short shelf life. Can anyone explain this? > >hydroxides (sodium, potassium, lithium etc) absorb carbon dioxide from > >the air. It beans you have less hydroxides but more carbonates.' I'm no chemist(footnote 1), but I have it on good authority that NaOH + CO2 => NaHCO3 & NaHC03 + NaOH => Na2C03 + H20 or 'lye exposed to air becomes baking soda and baking soda and lye become washing soda and water'. > Suppose you weigh 100 ml of a sodium hydroxide solution and find it > weighs 128.7 grams at 20 C. The weight percent of that solution is 26% > or 26 grams of sodium hydroxide per 100 grams of solution. I would have thought [IWHT?] specific gravity wouldn't be a good way to measure NaOH concentration in a questionably air-exposed sample. From the reaction above it seems every mole of NaOH absorbs one mole of CO2 and so the specific gravity would go ^up^ as the hydroxide solution [lye in water] degrades. Maybe diluting the solution with water and then measuring the pH would work without doing damage to the electrode [you could use pH paper and the electrode be damned]. Or dilute and titrate with acid to a neutral pH, the ratio of acid to NaOH solution giving the concentration of NaOH/Na2C03. One would have to back calculate from knowing the original concentration of NaOH to compensate for the Na2CO3 formed. If Na2CO3 is precipitating at the same time the NaOH/NaC03/H20 solution is being poured off then, well, it is probably easier to buy a new can of Red Devil and start over again. I use a small amount of 10% solution, though not for photography. It seems to keep just fine for a year in a plain-ole' brown plastic bottle (an old container that hypo-clear came in [Orbit Bath?]). A one pound can of Red Devil makes 5 quarts of 10% solution, enough to last a _long_ time, for me at least. If it were me, and it is, I would mix up a pint of 10% at a time and chuck it if it is over a year old. A 50% solution seems to be the chemists' answer, but I am too much of a slob to trust myself around a 50% solution. --- (1) I keep a copy of "University Chemistry" by Mahan in the bedroom bookcase. There is nothing like reading a chemistry text to put me to sleep: "Schrodinger ... sp2d3 orbitals ... enthalpy of formation ... Gibbs free energy ..." and it's "ZZZZZzzz" in 30 seconds flat. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm strength. > > [quoted text clipped - 31 lines] > > I don't grasp this logic. NaOH doesn't absorb CO2, it reacts with it. The combination of NaOH and CO2 also makes H20. 2 moles of NaOH and 1 mole of CO2 make 1 mole of Na2CO3 and 1 mole of HOH. If the carbonate precipitates, the specific gravity should go down as there is less solid and more water. >Maybe diluting the solution with water and then measuring the >pH would work without doing damage to the electrode [you could [quoted text clipped - 28 lines] > > Michael stated that carbonate is not soluble in highly concentrated hydroxide solution.. It will either settle or float. !0% is not any safer than 50%. 40% by weight is about as high as you can go with sodium. Solutions are, IMHO, safer than powder, which might be inhaled. The hydroxides are among the most useful and the most used compounds in the history of chemistry. They clean drains, wash clothes, make soap, are used in making dyes, and last but not least for us, are components in a number of very good developers. Why not learn all you can about them? My grandmother made soap with which she washed clothes every Saturday in water boiled over an open fire. > >From the reaction above it seems every mole of NaOH absorbs one > >mole of CO2 and so the specific gravity would go ^up^ as the > >hydroxide solution [lye in water] degrades. > I don't grasp this logic. NaOH doesn't absorb CO2, it reacts with it. Absorb is the wrong word, I was trying to convey the idea the lye solution takes CO2 from the air. > The combination of NaOH and CO2 also makes H20. 2 moles of NaOH and 1 > mole of CO2 make 1 mole of Na2CO3 and 1 mole of HOH. If the carbonate > precipitates, the specific gravity should go down as there is less solid > and more water. I thought I said that: > If Na2CO3 is precipitating at the same time the NaOH/NaC03/H20 > solution is being poured off then, well, it is probably easier > to buy a new can of Red Devil and start over again. > > If it were me, and it is, I would mix up a pint of 10% at a time and > > chuck it if it is over a year old. > 10% is not any safer than 50%. TTTH I have not dangled my left hand in a vat of 10% and my right in 50% to compare the results. > Why not learn all you can about hydroxides? My grandmother > made soap ... I imagine you did not teach your Grandmother how to make soap, Two years of University chemistry was enough for me. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm > > [quoted text clipped - 52 lines] > > Anyway, when you are handling any concentration of lye it would be a good isea to keep a bucket of vinegar handy. A saturated solution, with undissolved lye at the bottom, is pretty stable, and is easily checked. I use such solutions in making homebrewed Rodinal and similar concoctions. There are times when I want to measure the amount of hydroxide accurately, and weighing it in solution is probably more accurate for small amounts than any other method if the concentration is known. Nobody taught the first soap maker either, but the first one taught others. Cheers. >> >> [quoted text clipped - 67 lines] > > Cheers. My comment on safety was based on your statement that you were clutzy enough to be leary of handling the high concentrations but felt better with 10%. When I was a teenager back in the middle ages, I had a friend whose father would not let him own a BB gun, but bought him a .22 rifle and taught him how to use it. His reasoning was that the kid knew how dangerous the .22 was, but might get careless with a BB gun and put someone's eye out. Both solutions are potentially dangerous, but most people are more careful with the stronger one when the same care should be used with either. getting it on the hands is the least of the dangers. Inhaling dust or getting either dust or solution in the eyes is really bad. We agree that CO2 makes the NaOH solution weaker, but you said it increases the specific gravity, My point was that if the carbonate precipitates, the specific gravity decreases because some NaOH falls out at the same time water is increased. However, if the solution is saturated to begin with, with extra hydroxide precipitated, the water produced when CO2 reacts will dissolve more hydroxide, especially if the carbonate is insoluble in the saturated solution of hydroxide, so the solution stays saturated untill all the excess hydroxide has been dissolved. Now we have the problem of variation with temperature, but most of our uses will be near 20 C. My main reason for even bringing up the subject is that I had seen a formula used by AGFA around the time of WWII where the amounts of KOH and K2SO3 were expressed as weights of percentage solutions, and got to thinking about the advantages of this approach. Then this thread began asking about the storage life of hydroxide solutions. > We agree that CO2 makes the NaOH solution weaker, but you said it > increases the specific gravity, My point was that if the carbonate > precipitates, the specific gravity decreases because some NaOH falls out > at the same time water is increased. But the weight of the bottle increases. How it absorbs so much CO2 without evaporating is left as an exercise. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm > > [quoted text clipped - 8 lines] > > Well, it can't absorb any more than is in the bottle, once the bottle is sealed. It can't gain or lose weight, but the weight can be redistributed between solution and precipitate, if there is any. I guess I should add a little sodium carbonate to my saturated lye solution to see if it dissolves. > Nicholas O. Lindan wrote: > >"PATRICK GAINER" <pgainer@rtol.net> wrote > >But the weight of the bottle increases. How it absorbs so much CO2 > >without evaporating is left as an exercise. > Well, it can't absorb any more than is in the bottle, once the bottle > is sealed. Ah ha! The root of the difugalty: I have been assuming the bottle is open, else how can sufficient CO2 get to the solution. > It can't gain or lose weight Hence an open bottle gains wait by taking CO2 from the air and turning it into carbonate. And a closed bottle obviously doesn't. > I should add a little sodium carbonate to my saturated lye solution to > see if it dissolves. "Saturated"? Another sin [in the original sense ... I guess they must have shot bows and arrows in the Garden of Eden: A sin - what a thing to get tossed out on one's ear for.] I have been talking only of 10% solutions - if 50%'s don't go off why worry about them? IIRC this side spur started with finding ways to tell if a 10% NaOH solution had gone off. One was a change in specific gravity. It seems the answer is a mess: some water evaporates, some carbonate precipitates and some water is created over time and what the bottle of gunk weighs is anybody's guess. And does the carbonate precipitate if the solution is only 10% NaOH? And as the NaOH -> carbonate the carbonate can now go into solution as the concentration of the NaOH is falling: Ha! ==> The specific gravity of the _liquid_ will go up. The whole 'going off' thing seems a bit speculative: if enough air wafted by to supply CO2 sufficient to react with all the NaOH (say 2 oz/pt: 50gm/500ml) and NaOH is 40 (?-DIIMH) gm/mole, say 1 mole in the bottle. That takes 2 moles of CO2 -- 88 grams of C02; CO2 being 0.03% of air then ... oh this is getting to be too much, say 3 kilos of air - at around 1.3 oz/ft^3 6.6 x 16 / 1.3, about 80 ft^3 of air would have to be passed slowly through an aquarium aerator to consume all the NaOH. Under normal conditions I would hazard it would take a very long time for 80 cubic feet of air to wander in and out of a sealed bottle. If the solution goes from 10% to 9.5% over the years may matter to a chemistry lab where the NaOH solution is used for titration. I can't see it making much difference in photography. Or am I sinning wildly? I'm willing to set up a bottle of 10% and sample it in a year - if only we could find the right way to determine how much NaOH is left - and it's deja vu all over again. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm >"PATRICK GAINER" <pgainer@rtol.net> wrote > [quoted text clipped - 66 lines] > > A way to test a solution of NaOH is by titration with a known solution of acid. It's all relativity. How do you know the acid solution is any good? It's Godel's incompleteness theorem in practice. Who checks the checker? The original premise, which was proposed a couple of eons ago, (I reckon about 6 postings = 1 eon) was that the best way to be sure of a good solution of NaOH is to make it very concentrated. Much depends on what you want to use it for. I just did a little experiment. I blew my CO2 laden breath into my NaOH concentrate through a soda straw. The solution clouded up. I will try the same test on some 10% solution. It's almost as much fun as arguing about it. The trouble is, whichever way it comes out, we'll have to find something else to argue about. You got any ideas? > Nicholas O. Lindan wrote: > > > Nicholas O. Lindan wrote: > > > > > stuff > > > > more stuff > > > ever so much stuff > > will it ever stop > I just did a little experiment. I blew my > CO2 laden breath into my NaOH concentrate [50%? ed] > through a soda straw. The solution clouded up. Hey, no fair introducing reality. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. To reply, remove spaces: n o lindan at ix . netcom . com Fstop timer - http://www.nolindan.com/da/fstop/index.htm >"PATRICK GAINER" <pgainer@rtol.net> wrote > [quoted text clipped - 31 lines] > > Yes, ed. 500 g/liter of solution at 20 C, or 0.40 g/gram of solution. Enough to make a great gob of Rodinal. 1 great gob = 10 bunches. ------------------------------------------It does NOT work. NaOH always is contaminated by carbonates. The tables were drived from work under controlled atmsphere, without CO2. It does not occur in real world. it means you have x% of hydroxide and y% of carbonates and z% of water. Various quanities of these three can give the same spec. gravity. If you need to know the exact concentration of NaOH solution, you titrate with hydrochloric acid either using pH meter or two indicators. It allows you to calculate hydroxides and carbotes very accurately. #> #> #It may be of additional interest to know that it is not difficult to #determine the strength of a sodium or potassium hydroxide solution, #either in weight percent or weight per unit volume. Weigh a volume of #the solution measured at 20 C (68 F). Divide the weight by the volume #to get the specific gravity. Find in the CRC Handbook of Chemistry and #Physics the section that has tables called "CONCENTRATIVE PROPERTIES OF #AQUEOUS SOLUTIONS". #Suppose you weigh 100 ml of a sodium hydroxide solution and find it #weighs 128.7 grams at 20 C. The weight percent of that solution is 26% #or 26 grams of sodium hydroxide per 100 grams of solution. 1 liter #contains 334 grams at 20 C. These numbers are in the table. #In cases where high precicion is necessary, it will be better to weigh #out the amount you need, as the weight percentage does not vary with #temperature..The weight percentage as well as the weight per unit #volume can change due to aeration which precipitates some carbonate, but #this method uses only what remains dissolved, so it shold be a good way #to keep track of the strength. >------------------------------------------It does NOT work. NaOH >always is contaminated by carbonates. The tables were drived from work [quoted text clipped - 8 lines] > > OK. Tell me what titration separates hydroxide from carbonate. Do you know for a fact that carbonate is soluble in concentrated sodium hydroxide? Most laboratory stocks of NaOH are concentrated. The prevoius post shows that CO2 forms a precipitate in a concentrated solution of NaOH. The concentration of NaOH in the solution then determines the specific gravity. >#> >#> [quoted text clipped - 23 lines] >#to keep track of the strength. > ------------------------- #> #> #OK. Tell me what titration separates hydroxide from carbonate. Do you #know for a fact that carbonate is soluble in concentrated sodium #hydroxide? Most laboratory stocks of NaOH are concentrated. The prevoius #post shows that CO2 forms a precipitate in a concentrated solution of #NaOH. The concentration of NaOH in the solution then determines the #specific gravity. # sodium hydroxide and carbonate by Warder method tested solution containing 0.2-0.25 g of sodium hydroxide and 0.05-0.1 g of sodium carbonate dilute with water to 100 mL and cool down with water+crushed ice. Add 2 drops of 1% phenolphthalein indicator and titrate with 0.2 N HCl until solutionbecomes colorless (sharp end point from pink to colorless). Then add 2 drops of 0.1% methyl orange indicator and titrate with 0.2 N HCl to the first change of color from yellow to orange. In the first step you titrate all hydroxide and half of carbonate. In the second step you titrate the remaining half of carbonate. The first change of color is at pH 8.3, the second around 3.9. Carbonates=b mL (second step) x 2 x 0.053 x titer of HCl hydroxide = (a-b)mL x 0.0401 x N Warder's method is good for solutions high on hydroxides and low on carbonates. It is recommended method to test alkaline battery electrolyte (200 g/L KOH) contaminated with various quantities of potassium carbonate. Another method - titrate one lot with hydrochloric acid against mathyl orange, the second lot treat with barium chloride to precipitate carbonates and titrate again against phenolphthalein. Modification of the first method allows to determine carbonates and bicarbonates in one solution. For the fact I can tell you that 20% KOH will slowly absorb carbon dioxide. KOH will decrease and carbonates increase. I haven't seen anything above 150 g/L of potassium carbonate with remaining hydroxide without ptecipitation. But it happens in batteries left open for years. If you need solubility of carbonates in 50% hydroxide, search in library or Internet, I do not have it handy. In motion picture industry Kodak published figures to allow calculation of specific gravity a photographic solution . You multiply a factor by mass of a component as many times as the number of components. >------------------------- >#> [quoted text clipped - 53 lines] >number of components. > If I had a chemistry lab, I suppose I would have all the necessary indicators and standard solutions. The only way I can think of to test the use of specific gravity is to add to my concentrate an amount of anhydrous sodium carbonate to see how it affects the physical characteristics of the solution. That kind of test is not definitive except to show that the carbonate just lies at the bottom of the solution and the S.G. does not change within my ability to detect it. In less concentrated solutions, it is certainly possible to have a mixture of the hydroxide and the carbonate in solution. When CO2 is taken into a saturated solution, water is increased and NaOH makes the carbonate. The water is not enough to dissolve the carbonate, being only as much as you find in the monohydrated carbonate. If the carbonate precipitates, I would expect it to be in the monohydrated form. I think that a saturated solution with excess NaOH present will not form the carbonate in solution until all the excess NaOH has been dissolved. If I add solid NaOH from time to time, the solution should stay saturated with NaOH. |
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