| Pages:
1
2 |
JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
The product is still not dry, so I am drying it in an oven....
|
|
|
JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
Preparation of Calcium Hydroxide
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
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
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
National Hazard
Posts: 721
Registered: 16-3-2015
Member Is Offline
Mood: dooM
|
|
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
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
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
Hazard to Others
Posts: 392
Registered: 6-10-2013
Member Is Offline
Mood: No Mood
|
|
| 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
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
| 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]
|
|
|
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
