Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Calcium Sulphate Destroys Glassware
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 27-9-2021 at 17:04
Calcium Sulphate Destroys Glassware


Recently i've been doing a dry distillation of Calcium Nitrate with Sodium Bisulfate. It is a really convenient procedure to produce Ntric Acid (without any foaming) and also the resulting Calcium Sulfate does dissolve and come out of the flask at the end.

The problem I have is that the Calcium Sulphate seems to be adhering to my flasks and literally pulling borosilicate glass off the surface, then the next time I use that flask it ends up broken or cracked.

I am using Indian Supertek 500ml round bottom flasks in a heating mantle, am I suffering from poor glassware or just punishing it too much?

[Edited on 28-9-2021 by Chemgineer]
View user's profile View All Posts By User
MidLifeChemist
Hazard to Others
***




Posts: 183
Registered: 4-7-2019
Location: West Coast USA
Member Is Offline

Mood: precipitatory

[*] posted on 27-9-2021 at 18:56


I have heard of others being similarly punished by their calcium sulfate deposits. You are not alone. Still, if nitric acid is expensive and flasks are cheap where you live, then it might be worth it :)
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 28-9-2021 at 04:45


I might just add some water next time and accept a lower concentration.
View user's profile View All Posts By User
macckone
International Hazard
*****




Posts: 2129
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline

Mood: Electrical

[*] posted on 28-9-2021 at 12:53


Anecdotal:
Try adding some 90+% sulfuric acid, it seems to protect the glass.
I originally tried it to help dissolve the mix and reduce the amount of water carried over from non-anhydrous salts.
It seems to reduce the water and improve the reaction but I haven't done a quantitative study.
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 28-9-2021 at 13:26


Something else I considered was adding a percentage of Potassium Nitrate, as that reaction with Sodium Bisulfate causes foaming, the foam might help.
View user's profile View All Posts By User
Tsjerk
International Hazard
*****




Posts: 2744
Registered: 20-4-2005
Location: Netherlands
Member Is Offline

Mood: Mood

[*] posted on 28-9-2021 at 13:36


I think you heated the flask too much. I never distilled nitric acid from this mix, but when I did I never tried to pull the last bit.

Or it might have been the real anhydrous non-liquid combination between calcium sulfate and glass. I went with a percent of water and a second distillation from sulfuric acid anyway to get rid of the NO2. Although I don't know how a bit of water would have helped with CaSO4 as a drying agent in there
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 28-9-2021 at 13:54


I've done this with Potassium Nitrate and Sodium Bisulfate before several times using the same make of flask and no damage, I probably have kept the reaction going for longer with the Calcium Nitrate.. maybe it's because the calcium sulfate ends up drier than the mix of Sodium Sulfate and Potassium Sulfate and there is less heat sink for the glass which gets hotter. But to me it looks like the Calcium Sulfate has adhered to the glass surface and then retracted on cooling putting a layer with it.

[Edited on 28-9-2021 by Chemgineer]
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 28-9-2021 at 14:09


As in the photo there is a general dull area with an excavation of glass top right and then two cracks around the outside of the affected area.

IMG_20210928_230102a.jpg - 278kB
View user's profile View All Posts By User
Chemetix
National Hazard
****




Posts: 368
Registered: 23-9-2016
Location: Oztrayleeyah
Member Is Offline

Mood: Wavering between lucidity and madness

[*] posted on 28-9-2021 at 15:10


What you are experiencing is ion exchange in the glass. Strong concentrated solutions that have different ionic composition to glass will cause some surface ions to migrate.

Osmotic potential is the force behind the exchange. Sodium ions will want to move into the aqueous solution and calcium will try to move into the glass. Calcium makes the glass brittle. It becomes a glass with different coefficient of thermal expansion to the rest of the flask and so heating and cooling will cause stress at the boundaries where ion exchange has most strongly occurred.
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 28-9-2021 at 15:30


Hey thanks, what you say makes allot of sense and I expect you are correct. I suppose the good thing is the heating is applied gradually by the mantle and failure only seems to only occur on cooling when the calcium sulfate is a solid mass and can't spill from the flask.
View user's profile View All Posts By User
Amos
International Hazard
*****




Posts: 1387
Registered: 25-3-2014
Location: Yes
Member Is Offline

Mood: No

[*] posted on 28-9-2021 at 16:10


Does calcium sulfate not readily precipitate when you combine the two reagents? If it does, there's no reason to leave it in the flask while you distill; vacuum filter it first and distill the filtrate. If you lack vacuum filtration capabilities, I would add more water as you mentioned and still manually gravity filter. You won't distill the last bits of nitric acid out of the mixture until the dissolved salt content has nearly reached saturation, and this will be the most concentrated distillate of the entire process.
View user's profile View All Posts By User
Texium
Administrator
********




Posts: 3802
Registered: 11-1-2014
Location: Salt Lake City
Member Is Online

Mood: Triturated

[*] posted on 29-9-2021 at 05:39


He said he’s doing it as a dry distillation, which would seem to be a horribly inefficient and potentially dangerous method, but oh well. So currently he’s not adding any water at all, just heating the solid mixture in a flask.

@Chemgineer: What sort of yields do you get with this dry distillation? If “foaming” is really such an insurmountable issue with the aqueous procedure, I would suggest investing in a larger boiling flask… Also, could you please stop Capitalizing Your Chemical Names? They are not proper nouns, and writing them that way just looks pretentious.




Come check out the Official Sciencemadness Wiki
They're not really active right now, but here's my YouTube channel and my blog.
View user's profile Visit user's homepage View All Posts By User
Metallophile
Hazard to Self
**




Posts: 68
Registered: 23-3-2018
Member Is Offline

Mood: No Mood

[*] posted on 29-9-2021 at 08:02


Quote: Originally posted by Texium  
They are not proper nouns,


I have made this mistake before. I think it's actually kinda strange that elements are not proper nouns, even the ones named after people! But that's the rule, so I try to follow it.
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 29-9-2021 at 08:42


Quote: Originally posted by Texium  
He said he’s doing it as a dry distillation, which would seem to be a horribly inefficient and potentially dangerous method, but oh well. So currently he’s not adding any water at all, just heating the solid mixture in a flask.

@Chemgineer: What sort of yields do you get with this dry distillation? If “foaming” is really such an insurmountable issue with the aqueous procedure, I would suggest investing in a larger boiling flask… Also, could you please stop Capitalizing Your Chemical Names? They are not proper nouns, and writing them that way just looks pretentious.


I use 160g sodium bisulfate and 100g of calcium nitrate and I typically get around 50ml of RFNA.

# Edited to remove my capital letters!

[Edited on 29-9-2021 by Chemgineer]
View user's profile View All Posts By User
Fulmen
International Hazard
*****




Posts: 1576
Registered: 24-9-2005
Member Is Offline

Mood: Bored

[*] posted on 29-9-2021 at 09:15


What's the temperature? With thoroughly dried chems I would guess you would need to melt the bisulphate (315°C). There are nitrate eutectics that melt at much lower temperatures, might be worth a shot.



KNO3 NaNO3 Ca(NO3)2 MP
24.............................76...........142
.................31............69...........142
26.............................74...........145
65............................ 35...........150
46.............24............30...........160
20.............................80...........162
.................19............81...........214
.................14............86...........214
40.............60...........................222




We're not banging rocks together here. We know how to put a man back together.
View user's profile View All Posts By User
Texium
Administrator
********




Posts: 3802
Registered: 11-1-2014
Location: Salt Lake City
Member Is Online

Mood: Triturated

[*] posted on 29-9-2021 at 10:53


Quote: Originally posted by Chemgineer  
I use 160g sodium bisulfate and 100g of calcium nitrate and I typically get around 50ml of RFNA.
That would be about a 98% yield based on calcium nitrate, if we assumed that what you collect is 100% nitric acid, but since RFNA contains additional dissolved NO2, that amount wouldn’t even be possible to obtain from that amount of reagents… Are you sure you’re using anhydrous calcium nitrate? If not, you likely aren’t getting true RFNA.



Come check out the Official Sciencemadness Wiki
They're not really active right now, but here's my YouTube channel and my blog.
View user's profile Visit user's homepage View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 29-9-2021 at 11:56


Quote: Originally posted by Texium  
Quote: Originally posted by Chemgineer  
I use 160g sodium bisulfate and 100g of calcium nitrate and I typically get around 50ml of RFNA.
That would be about a 98% yield based on calcium nitrate, if we assumed that what you collect is 100% nitric acid, but since RFNA contains additional dissolved NO2, that amount wouldn’t even be possible to obtain from that amount of reagents… Are you sure you’re using anhydrous calcium nitrate? If not, you likely aren’t getting true RFNA.


Not fully anhydrous no, this probably helps keep the temperatures lower, the product does fume though when opening a closed bottle.
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 29-9-2021 at 14:04


Ok i've just measured the specific gravity with a measuring cylinder and scales, the HNO3 from calcium nitrate seems to be 1.41 sg @ 18 deg C which would make it 68%..... so azeotropic.

My previous HNO3 from a similar dry process with potassium nitrate and sodium bisulfate comes in at 1.46 sg @18 deg C which would make it 81%.
View user's profile View All Posts By User
rockyit98
National Hazard
****




Posts: 283
Registered: 12-4-2019
Location: The Known Universe
Member Is Offline

Mood: no mood is a good mood

[*] posted on 29-9-2021 at 15:52


you doing it wrong. you need to add H2SO4 to concentrated Solution of Ca(NO3) slowly while mixing. CaSO4 will precipitate out. remove them and distill the dilute solution till azeotropic forms.



"A mind is a terrible thing to lose"-Meisner
View user's profile View All Posts By User
Amos
International Hazard
*****




Posts: 1387
Registered: 25-3-2014
Location: Yes
Member Is Offline

Mood: No

[*] posted on 30-9-2021 at 14:45


Quote: Originally posted by rockyit98  
you doing it wrong. you need to add H2SO4 to concentrated Solution of Ca(NO3) slowly while mixing. CaSO4 will precipitate out. remove them and distill the dilute solution till azeotropic forms.


It should be very obvious that sulfuric acid isn't easy to come by for the OP, or they wouldn't be attempting to make nitric acid this way.
View user's profile View All Posts By User
clearly_not_atara
International Hazard
*****




Posts: 2305
Registered: 3-11-2013
Member Is Offline

Mood: Big

[*] posted on 30-9-2021 at 16:13


If you want to do a dry distillation, you can probably protect your glassware by using a eutectic mixture of sodium and potassium bisulfate instead of just one or the other.

Eutectic (44% KHSO4 by moles; 50% by mass): 133 C [1]
NaHSO4: 315 C [2]
KHSO4: 197 C [2]

1:
https://www.researchgate.net/publication/230557353_Conductiv...
2: Wikipedia




[Edited on 04-20-1969 by clearly_not_atara]
View user's profile View All Posts By User
Amos
International Hazard
*****




Posts: 1387
Registered: 25-3-2014
Location: Yes
Member Is Offline

Mood: No

[*] posted on 2-10-2021 at 10:09


Quote: Originally posted by clearly_not_atara  
If you want to do a dry distillation, you can probably protect your glassware by using a eutectic mixture of sodium and potassium bisulfate instead of just one or the other.

Eutectic (44% KHSO4 by moles; 50% by mass): 133 C [1]
NaHSO4: 315 C [2]
KHSO4: 197 C [2]


If the reaction is successful though, bisulfates will still end up as solid sulfates
View user's profile View All Posts By User
Antiswat
International Hazard
*****




Posts: 1585
Registered: 12-12-2012
Location: Dysrope (aka europe)
Member Is Offline

Mood: dangerously practical

[*] posted on 22-10-2021 at 04:19


i had some distillation mixture of H2SO4 and CaSO4 standing around
i dumped it into a plastic bottle to be situated next to my toilet, to help remove calcium deposits every now and then
about a year later i found the bottle again
and there was about a fist-sized chunk of crystals in there
i eventually found out it was CaSO4 crystals
https://gyazo.com/74e95b60263131dfad29986ace145977

now what i understand is that i hit a particular H2SO4 concentration in which CaSO4 is soluble in
and upon diluting this further, it precipitated out the CaSO4, very slowly
so there must be maybe 10-20% "sweetspot" with H2SO4/H2O concentration in which CaSO4 is soluble.

so that might work for ya.

i would say maybe 20% or even less is where the CaSO4 dissolve- its only a vague guess




~25 drops = 1mL @dH2O viscocity - STP
Truth is ever growing - but without context theres barely any such.

https://en.wikipedia.org/wiki/Solubility_table
http://www.trimen.pl/witek/calculators/stezenia.html
View user's profile View All Posts By User
Chemgineer
Hazard to Self
**




Posts: 76
Registered: 25-5-2021
Member Is Offline


[*] posted on 12-11-2021 at 07:58


Quote: Originally posted by Chemetix  
What you are experiencing is ion exchange in the glass. Strong concentrated solutions that have different ionic composition to glass will cause some surface ions to migrate.

Osmotic potential is the force behind the exchange. Sodium ions will want to move into the aqueous solution and calcium will try to move into the glass. Calcium makes the glass brittle. It becomes a glass with different coefficient of thermal expansion to the rest of the flask and so heating and cooling will cause stress at the boundaries where ion exchange has most strongly occurred.


I am wondering if the quality of the glass might have a bearing on this issue, the flasks which I have seen fail are all from the same manufacturer (supertek) and were quite cheap. I've noticed in other reactions that better quality flasks such as Quickfit or Glassco brand seem to be more none stick on the inside surface so possibly a smoother surface finish.

I'm just not quite ready to risk a better flask to failure on this reaction yet!
View user's profile View All Posts By User
bluamine
Hazard to Others
***




Posts: 154
Registered: 17-8-2015
Member Is Offline

Mood: No Mood

[*] posted on 15-1-2022 at 18:27


In such a temperature degree you'll end up with some 'burnt' plaster which even doesn't get hydrated!!!
@clearly_not_atara: does this method make the glassware "passive"?
Wikipedia mentions that calcium sulfate is slightly soluble in warm hydrochloric acid if my memory is still good, it may help you @chemingeneer
View user's profile View All Posts By User

  Go To Top