Sciencemadness Discussion Board

OTC Calcium Hydroxide

JJay - 27-10-2015 at 13:08

Where is a good place to obtain small quantities of calcium hydroxide OTC? I've heard and read that it is sometimes available in food grade as "pickling lime" for preparing crisp pickles, but I checked several health food, craft, brewing, department, grocery, and home improvement stores and didn't find any pickling lime. Technical grade Ca(OH)2 It is available very inexpensively from home improvement and gardening stores as "hydrated lime," but they generally sell it in large quantities, and I don't want to store more than a couple of kilograms.

Any ideas?

Bert - 27-10-2015 at 13:25

Um, make it yourself?

http://www.lowtechmagazine.com/2013/09/lime-kilns.html

byko3y - 27-10-2015 at 13:26

In fact they sell something which is not a hydrated lime, but a mixture of CaCO3+Ca(OH)2. So I've got no source of OTC Ca(OH)2 too, I'm forced to make it from CaCl2 and NaOH.

JJay - 27-10-2015 at 13:37

Ca(OH)2 is much more soluble in water than CaCO3, right?

violet sin - 27-10-2015 at 13:47

Gardening shop. 10# bag of hydrated(slacked) lime for $ 1.95 isn't bad.

RareEarth - 27-10-2015 at 13:48

Calcium Salts usually have very poor solubility in water, in my experience. According to wikipedia this seems to be the case for both Calcium Hydroxide and Carbonate

JJay - 27-10-2015 at 14:21

Calcium hydroxide is 100x as soluble in water as calcium carbonate... but the hydroxide's solubility is low too... less than 2 grams will dissolve in a liter of water....

Mixing NaOH and CaCl2 looks like it will work well for creating pretty darn pure Ca(OH)2.

[Edited on 27-10-2015 by JJay]

Magpie - 27-10-2015 at 14:21

Safeway grocery stores and Ace hardware sell pickling lime in my city. I can also buy hydrated lime by the pound at my local garden stores - bring your own container.

[Edited on 27-10-2015 by Magpie]

RareEarth - 27-10-2015 at 14:30

Quote: Originally posted by JJay  
Calcium hydroxide is 100x as soluble in water as calcium carbonate... but the hydroxide's solubility is low too... less than 2 grams will dissolve in a liter of water....

Mixing NaOH and CaCl2 looks like it will work well for creating pretty darn pure Ca(OH)2.

[Edited on 27-10-2015 by JJay]


Given the solubilities, I would agree. But, where do you plan to get CaCl2, that you can't also get Ca(OH)2?

careysub - 27-10-2015 at 14:34

Latin markets sell calcium hydroxide as "cal" or "cal mexicana". It is used to treat corn (nixtamalization) to make masa (corn dough).

Not all regions have equal access to Latin markets of course.

[Edited on 27-10-2015 by careysub]

[Edited on 27-10-2015 by careysub]

j_sum1 - 27-10-2015 at 14:37

Quote: Originally posted by RareEarth  
Quote: Originally posted by JJay  
Calcium hydroxide is 100x as soluble in water as calcium carbonate... but the hydroxide's solubility is low too... less than 2 grams will dissolve in a liter of water....

Mixing NaOH and CaCl2 looks like it will work well for creating pretty darn pure Ca(OH)2.

[Edited on 27-10-2015 by JJay]


Given the solubilities, I would agree. But, where do you plan to get CaCl2, that you can't also get Ca(OH)2?

My supermarket, which is within walking distance of my home, sells NaOH and CaCl2. I don't think they sell Ca(OH)2.
But, point taken. Ca(OH)2 should not be too difficult to find.

violet sin - 27-10-2015 at 15:01

Damp-rid is CaCl2 prills for moisture control sold at rite-ade in the camping department for under 2$.

JJay - 27-10-2015 at 15:01

Something like this....


Preparation of Calcium Hydroxide (experimental)

Every time reagents are mixed in this procedure, the resulting solution will get hot, so add reagents slowly.

Place 100 mL distilled H2O in a 250 mL beaker. Carefully add 40.00 g NaOH with stirring until it dissolves. In a 500 mL beaker, place 100 mL H2O and add 55.49 g anhydrous CaCl2 with stirring until all CaCl2 dissolves. Add NaOH solution to CaCl2 solution with vigorous stirring. Ca(OH)2 crystals will precipitate. Rinse 250 mL beaker with 10 mL H2O to ensure that all NaOH is added to the reaction mixture; when both solutions are completely mixed, pH of the result should be slightly basic. Filter the reaction mixture while still hot and wash with hot H2O. Dry the crystals and calculate the yield.

[Edited on 27-10-2015 by JJay]

[Edited on 27-10-2015 by JJay]

[Edited on 27-10-2015 by JJay]

JJay - 27-10-2015 at 15:19

If someone wants to check my stoichiometry and make sure I didn't accidentally try to dissolve 10x too much of a compound in distilled water before I actually try out this procedure, be my guest.

RareEarth - 27-10-2015 at 15:30

I don't see anything wrong. To ensure maximum conversion of the NaOH, it wouldn't hurt to use excess CaCl2. Any leftover will just stay dissolved in the water with the NaCl anyways. Wouldn't make too much of a difference, but wouldn't hurt either.

gdflp - 27-10-2015 at 15:32

I don't think that will work. The stoichiometry looks right, but calcium hydroxide doesn't cleanly precipitate out of such concentrated solutions. Instead of an easily filterable precipitate, you will get something with around the consistency of toothpaste. I would dilute the solutions at least 5x to get a successful reaction mixture which will filter easily.

violet sin - 27-10-2015 at 15:36

Don't think the CaCl2 is anhydrous in damprid. So unless you have a source specifically stating it's purity and hydration, weights may be a touch off. I seem to remember reading it was often sold as a lower hydrate that still allowed it to absorb moisture. I'll look around later on the laptop, phone use to scrounge up data sux.

DistractionGrating - 27-10-2015 at 15:41

Google "kalkwasser for sale".

JJay - 27-10-2015 at 15:43

Quote: Originally posted by gdflp  
I don't think that will work. The stoichiometry looks right, but calcium hydroxide doesn't cleanly precipitate out of such concentrated solutions. Instead of an easily filterable precipitate, you will get something with around the consistency of toothpaste. I would dilute the solutions at least 5x to get a successful reaction mixture which will filter easily.


This seems like very sound and reasonable advice. Mixing more dilute solutions will be safer too.

[Edited on 27-10-2015 by JJay]

NedsHead - 27-10-2015 at 15:47

The last time I needed a small amount of calcium hydroxide I drove to the nearest housing development area and politely asked a brick layer, he put a shovel full into a bag for me and refused to take a cent for it.

Any housing development happening near you?

JJay - 27-10-2015 at 16:00

Quote: Originally posted by RareEarth  
I don't see anything wrong. To ensure maximum conversion of the NaOH, it wouldn't hurt to use excess CaCl2. Any leftover will just stay dissolved in the water with the NaCl anyways. Wouldn't make too much of a difference, but wouldn't hurt either.


I agree.

JJay - 28-10-2015 at 08:58

I'm going to carry out the following procedure:

Preparation of Calcium Hydroxide (experimental)

Place 100 mL H2O in a 250 mL beaker. Carefully add 8.00 g NaOH with stirring until it dissolves. In a 500 mL beaker, place 100 mL H2O and add 30 g dry tech grade CaCl2 (as ice melt) with stirring until all CaCl2 dissolves. Add NaOH solution to CaCl2 solution with vigorous stirring. Ca(OH)2 will precipitate. Rinse 250 mL beaker with 10 mL H2O to ensure that all NaOH is added to the reaction mixture; when both solutions are completely mixed, pH of the result should be slightly basic. Measure and record the pH and temperature. Filter the reaction mixture while still hot and wash with hot H2O. Dry the crystals in a sealed container over CaCl2 and calculate the yield.

JJay - 28-10-2015 at 09:08

If I wanted an analytically pure product, I think I would purify the NaOH by crystalizing it from methanol (probably not necessary) and purify the Ca(OH)2 by crystalizing it from glycerine.

Deathunter88 - 28-10-2015 at 09:31

Nile Red's video might be helpful.
http://www.youtube.com/watch?v=G26uzosONGk

(Nile Red's video, not mine)

JJay - 28-10-2015 at 15:09

I performed the experiment. It was successful; I am waiting for the product to dry so I can calculate the yield.

JJay - 29-10-2015 at 00:09

The product is still not dry, so I am drying it in an oven....

Preparation of Calcium Hydroxide

JJay - 29-10-2015 at 01:04

100 mL of distilled water was placed a 250 mL beaker. 8.00 grams of NaOH was added. The mixture was placed under stirring until the NaOH dissolved completely. Then an additional 100 mL of distilled water was placed in a 500 mL beaker. 30.09 grams of CaCl2 was added to the second beaker, and the resulting mixture was placed under stirring until the CaCl2 dissolved completely. Then the NaOH solution from the first beaker was added. It is difficult to add the NaOH solution slowly by decantation; use of a pipette may simplify addition. The warm reaction mixture took on a milky white appearance. The 250 mL beaker was rinsed with approximately 10 mL of distilled H2O, and the rinse water was added to the reaction mixture. It was stirred for a few minutes and then filtered. A low-quality hand-powered vacuum pump was found to be largely ineffective for removing the filtrate from the product, so an electric vacuum pump was used instead. The filtrate was translucent with a small amount of product that was deemed unrecoverable, so it was discarded. The filter cake was washed with 100 mL of boiling distilled water in small portions and then removed from the filter paper and dried to constant weight in an oven at 300 C. Yield: 6.84 grams (92.3%).

[Edited on 29-10-2015 by JJay]

JJay - 29-10-2015 at 01:31

A couple of notes...

There were some mechanical losses; it is possible to obtain a slightly higher yield.

The filtrate contains rather common and innocuous substances... water, salt, calcium chloride, and calcium hydroxide. It can be safely disposed of by pouring it down the drain.

The product will be hard to gravity filter. It's easy to filter with a good vacuum source and a Buchner funnel; with the proper equipment, a significantly higher concentration of NaOH could be used, which would improve yields, though it could negatively affect purity. Red Nile allowed mixtures of the product to settle and used decantation to remove liquid. Depending on what equipment is available, that may be a more practical approach to working up the product than filtration.

byko3y - 29-10-2015 at 18:55

Ca(OH)2 powder absorbs CO2 from the air as crazy That's another reason not to use filtration, but decantation. Vacuum or dessicator with NaON should be used to prepare a pure dry Ca(OH)2. Otherwise you can just use a wet one, because its powdered form is much more reactive towards air.

JJay - 29-10-2015 at 20:36

Quote: Originally posted by byko3y  
Ca(OH)2 powder absorbs CO2 from the air as crazy That's another reason not to use filtration, but decantation. Vacuum or dessicator with NaON should be used to prepare a pure dry Ca(OH)2. Otherwise you can just use a wet one, because its powdered form is much more reactive towards air.


The carbon dioxide concentration in air is pretty low. I used a desiccator filled with CaCl2 for several hours, but it didn't dry the product as quickly as I wanted, so I used heat.

Upsilon - 30-10-2015 at 05:07

Quote: Originally posted by JJay  

The carbon dioxide concentration in air is pretty low. I used a desiccator filled with CaCl2 for several hours, but it didn't dry the product as quickly as I wanted, so I used heat.


Don't underestimate carbon dioxide in the air. While concentration is low, hydroxides tend to have an insatiable affinity for it. As long as you don't leave it out for long, it should be fine. But I left a KOH solution out in air for multiple days, and when I went to neutralize it with acid, it fizzed like crazy due to the K2CO3 that formed.

Luckily, in your case if CaCO3 forms then it can easily be filtered out since it is much less soluble than Can(OH)2

JJay - 30-10-2015 at 21:41

Quote: Originally posted by Upsilon  
Quote: Originally posted by JJay  

The carbon dioxide concentration in air is pretty low. I used a desiccator filled with CaCl2 for several hours, but it didn't dry the product as quickly as I wanted, so I used heat.


Don't underestimate carbon dioxide in the air. While concentration is low, hydroxides tend to have an insatiable affinity for it. As long as you don't leave it out for long, it should be fine. But I left a KOH solution out in air for multiple days, and when I went to neutralize it with acid, it fizzed like crazy due to the K2CO3 that formed.

Luckily, in your case if CaCO3 forms then it can easily be filtered out since it is much less soluble than Can(OH)2


Unless the product is left out for days or the sodium hydroxide is impure, CaCO<sub>3</sub> is unlikely to be contaminate the product in large quantities.

It is possible to use differences in solubilities to remove the CaCO<sub>3</sub>, but if you use water, it will require large volumes. It is easier to keep contaminants out of Ca(OH)<sub>2</sub> than it is to remove them.

[Edited on 31-10-2015 by JJay]