NaOH question

Nicholas O. Lindan wrote:

"PATRICK GAINER" wrote



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.



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.

"PATRICK GAINER" wrote
Nicholas O. Lindan wrote:
"PATRICK GAINER" 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.

--
Nicholas 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

Nicholas O. Lindan wrote:

"PATRICK GAINER" wrote


Nicholas O. Lindan wrote:


"PATRICK GAINER" 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.



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?

"PATRICK GAINER" wrote
Nicholas O. Lindan wrote:
"PATRICK GAINER" wrote
Nicholas O. Lindan wrote:
"PATRICK GAINER" 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.

--
Nicholas 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

Nicholas O. Lindan wrote:

"PATRICK GAINER" wrote


Nicholas O. Lindan wrote:


"PATRICK GAINER" wrote


Nicholas O. Lindan wrote:


"PATRICK GAINER" 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.



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.

nailer wrote:

On Sat, 21 Jan 2006 17:35:18 -0500, PATRICK GAINER
wrote:

------------------------------------------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.



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.

#
#
#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.

nailer wrote:

On Tue, 24 Jan 2006 16:39:04 -0500, PATRICK GAINER
wrote:

-------------------------
#
#
#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.


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.