Sciencemadness Discussion Board

Identifying your calcium ammonium nitrate

KoiosPhoebus - 24-1-2023 at 06:30

Hi everyone! This is my first post here, apologies if this is in the wrong forum or if I'm not doing something right. Please do tell me if that's the case!

I have a little background in working with chemicals used in agriculture/horticulture so that's probably what I'll be mostly posting about.

Annoyingly, "calcium ammonium nitrate" is used to refer to two very different types of chemicals; in some parts of the world they even refer to both as "calcium nitrate", adding another two chemicals' worth of confusion. The possible makeup of "calcium ammonium nitrate" is usually either:
  • NH4NO3 + CaCO3, in varying ratios (sometimes CaSO4)
  • 5 Ca(NO3)2.NH4NO3.10 H2O

Depending on where you are, "calcium nitrate" may refer to:
  • 5 Ca(NO3)2.NH4NO3.10 H2O
  • Ca(NO3)2.4 H2O
  • Ca(NO3)2 (anhydrous, may contain trace NH4NO3)

So how do you tell which "calcium nitrate" you're working with?

Hints on the packaging
All fertilizers typically declare how much nitrogen is in there by weight (the 'N' in 'NPK'). If the fertilizer says 15-0-0, or 15.5-0-0, you're probably working with the double salt 5 Ca(NO3)2.NH4NO3.10 H2O. If it says something like 11-0-0 or 11.9-0-0, you're working with the tetrahydrate (Ca(NO3)2.4 H2O) while 17-0-0 is usually the anhydrous salt. To confirm which chemical you're working with, we can use two tests:

First test: Water solubility
Apart from the first formulation (NH4NO3 + CaCO3), all of the other calcium nitrates should be very water-soluble. If you dissolve your calcium ammonium nitrate in water and get a milky solution, you probably have a mix of ammonium nitrate and a calcium salt.

Recovering the calcium salt from this formulation is reasonably easy due to it typically being rather insoluble in water. If the calcium salt is CaCO3 (it'll bubble if you add an acid to it), adding a small amount of aqueous ammonia can help to get all of it out of solution by raising the pH - the ammonia will evaporate from the remaining solution upon drying. Whether the calcium salt is CaCO3 or CaSO4, recrystallisation in hot ethanol should precipitate out anything which dissolved in water.

Second test: Acetone solubility
What if the calcium nitrate you're working with is water-soluble? Then, you might be working with either the double salt (which contains ammonium nitrate) or straight calcium nitrate.

To determine the difference, you should try dissolving the fertilizer in acetone (if they come in prills/granules, grind it down to a powder first). Ammonium nitrate is practically insoluble in acetone (0.5 g/100 g acetone) while calcium nitrate is very soluble in acetone (33 g/100 g acetone) - see this paper for more detail on the solubility of various nitrates in acetone: Spectra of Inorganic Nitrates in Acetone and the Use of Such Spectra in Analytical Chemistry.

Add about 1-2 grams to 10 g acetone (or 13 mL acetone), stir for a bit, and let it sit. If a precipitate falls out of solution, you're probably working with the ammonium-containing version. This method can also be used to separate the calcium nitrate from the ammonium nitrate when working with the double salt (5 Ca(NO3)2.NH4NO3.10 H2O), and I've also seen it used in preparing the anhydrous version (which is why some anhydrous calcium nitrate fertilizers declare 0.2% ammonium nitrogen on their packaging - ammonium nitrate has low solubility in acetone but is still slightly soluble).

Hope some of you found this helpful! I'm not sure if something similar was posted elsewhere, I did a search of the forums for calcium ammonium nitrate and didn't find anything.

charley1957 - 24-1-2023 at 12:02

(Quote)Hi everyone! This is my first post here, apologies if this is in the wrong forum or if I'm not doing something right. Please do tell me if that's the case!

I used to inhabit another chemistry forum where the powers that be there would regularly beat up on newbies for this very thing, constantly admonishing them to reread the forum rules, or for not using proper subscript notation when they don’t enforce that with more established members, etc. It got to where I finally went to war with them about it. Of course then I was the one who was wrong and was also admonished to go reread the forum rules, blah blah blah. I no longer frequent that forum except to occasionally see if they’re still treating newbies that way. Last time I checked about two months ago, they still do it. I suspect that’s why we see these apologies here from newbies so often. I like to think we treat our newbies with a lot more respect. Welcome, KoiosPhoebus!

KoiosPhoebus - 25-1-2023 at 18:21

Quote:

Welcome, KoiosPhoebus!

Thanks for the welcome, charley!

KoiosPhoebus - 30-1-2023 at 19:44

I should add that another way to check if a water-soluble calcium nitrate contains ammonium nitrate would be to add a moderate-to-strong base and check for ammonia fumes using a wet litmus paper. Typically such bases include NaOH, KOH or Ca(OH)2/CaO. The calcium bases can be used to convert ammoniated calcium nitrate to straight calcium nitrate:

2 (5 Ca(NO3)2.NH4NO3.10 H2O) + Ca(OH)2 > 11 Ca(NO3)2 + 2 NH3 (g) + 22 H2O

While bases like NaOH or KOH can be used to generate the relevant nitrate:

5 Ca(NO3)2.NH4NO3.10 H2O + xOH > 5 Ca(NO3)2 + xNO3 + NH3 (g) + 21 H2O

Sodium nitrate and potassium nitrate both have very low solubility in acetone (0.024 g / 100 g acetone and 0.015 g / 100 g acetone respectively - see the paper referenced in the first post), so they can be extracted by recrystallisation in acetone. This test for ammonium therefore can also be used as a way of generating the relevant nitrate, especially if excess base is used:

5 Ca(NO3)2.NH4NO3.10 H2O + 11 xOH > 5 Ca(OH)2 + 11 xNO3 + NH3 (g) + 21 H2O

(where x = Na, K)

The resulting calcium hydroxide has low solubility in water and should therefore precipitate out. You can get even better results by leaving the solution exposed to air (or, heck, by exhaling on it a few times, before adding the base) - this allows the solution to pick up carbon dioxide and converts the somewhat-insoluble calcium hydroxide to a very-insoluble calcium carbonate which precipitates at even greater rates.

yobbo II - 31-1-2023 at 08:42


'Calcium Ammonium Nitrate' CAN is usually a mixture of Ammonium Nitrate and Calcium Carbonate in Europe.
Containing 27 or 27.5% N.

Pure 100% Ammonium Nitrate is (I think, look it up) 34% N.

There will be no K in the bag or they will bost about it (it is expensive).
The bag will tell you how much Nitric nitrogen (the stuff in the nitrate part of the molecule/mixture) the how much Ammonical nitrogen (the stuff in the ammonium part of the molecule/mixture)

No N in the Ca Carbonate of course

Yob


[Edited on 31-1-2023 by yobbo II]

KoiosPhoebus - 31-1-2023 at 17:08

Quote: Originally posted by yobbo II  

'Calcium Ammonium Nitrate' CAN is usually a mixture of Ammonium Nitrate and Calcium Carbonate in Europe.
Containing 27 or 27.5% N.

Pure 100% Ammonium Nitrate is (I think, look it up) 34% N.

There will be no K in the bag or they will bost about it (it is expensive).
The bag will tell you how much Nitric nitrogen (the stuff in the nitrate part of the molecule/mixture) the how much Ammonical nitrogen (the stuff in the ammonium part of the molecule/mixture)

No N in the Ca Carbonate of course

Yob


[Edited on 31-1-2023 by yobbo II]


Yep, as I point out above, the variants of "calcium ammonium nitrate" with 17-0-0 or less nitrogen are typically calcium nitrate based mixtures, not ammonium nitrate based mixtures. I'm just pointing out the acetone solubility + adding alkali tests as useful ways to determine if the CAN/CN contains ammonium nitrate as part of its mix or is straight calcium nitrate.

Unfortunately outside Europe things get a lot more muddy. I've even seen mixes of calcium carbonate, ammonium nitrate and ammonium sulphate marketed as "calcium ammonium nitrate". This is annoying but isn't too bad I suppose - you can test/separate this by recrystallising from water (producing ammonium sulphate/ammonium nitrate), then trying to dissolve it in absolute ethanol (AN dissolves at about 3g/100g ethanol at room temp, AS has minimal solubility).

Chemgineer - 1-2-2023 at 12:07

Also worth searching for an MSDS material safety datasheet for your particular brand of fertilizer, that should give you details of the active ingredients.

yobbo II - 2-2-2023 at 08:05


There is also a double salt Calcium Nitrate + Ammonium Nitrate that one poster here somehwhere turned up in a bag of fertilizer.

https://www.fertiberia.com/en/agriculture/products/categorie... a bit vague as usual??
and
https://en.crystalls.info/Calcium-ammonium_nitrate

Chemical equation:
NH4NO3 + 5Ca(NO3)2 = 5Ca(NO3)2 · NH4NO3


For preparation of 100.00g of calcium-ammonium nitrate decahydrate а 109.26g of calcium nitrate tetrahydrate and 7.41g of ammonium nitrate is required.

Dissolve compounds in hot water apart and then mix solutions into one container with intense stirring. Cooling or evaporation of a solution will cause double salt crystallyzation.

Yob

KoiosPhoebus - 2-2-2023 at 21:01

Quote: Originally posted by Chemgineer  
Also worth searching for an MSDS material safety datasheet for your particular brand of fertilizer, that should give you details of the active ingredients.


Agreed, that can often be quite helpful but is sometimes misleading, intentionally or otherwise. For example, a bottle of iron sulfate fertilizer I bought recently which was supposed to be iron (II) sulfate monohydrate (>90% purity). However, the nutrient analysis was really weird - the % iron was more similar to that of iron (III) sulfate monohydrate while the % sulfur was more similar to that of iron (II) sulfate monohydrate. When I finally got around to using it, it formed a yellow solution and was only somewhat soluble - ferrous sulfate is supposed to produce green solutions and is highly soluble. My guess is that maybe the iron (II) sulfate monohydrate oxidised to various ferric salts, or the company actually blended ferric salts into the fertiliser to get a higher iron content.

Additionally, I recently picked up a fertilizer which claimed to be 17-0-0 calcium nitrate and whose SDS claimed it was calcium nitrate, not the double salt calcium ammonium nitrate. However, when I tested it for ammonia using an aquarium NH3 test and compared it to an equal mass of 15.5-0-0 CAN, it had the same amount of ammonia as the double salt. So SDSes can definitely be useful, but a lot of the time, fertilizers are repacked and resold by distributors who may not know a lot about the chemistry of what they're selling.

yobbo II - 3-2-2023 at 13:55


Ferrrous sulphate is inclined to oxidize a bit when you dissolve in water and you can get yellow colour.
If you acidify the water this will not happen.

SnailsAttack - 3-2-2023 at 22:31

Nice writeup, these are all good tests. It's interesting that calcium nitrate is so soluble in acetone while ammonium isn't.

KoiosPhoebus - 5-2-2023 at 00:13

Quote: Originally posted by yobbo II  

Ferrrous sulphate is inclined to oxidize a bit when you dissolve in water and you can get yellow colour.
If you acidify the water this will not happen.


There's a lot of precipitate when I dissolve it in water, which is another reason I doubt that the material is actually ferrous sulphate. Below, I dissolve less than 1 g in 100 mL of boiled demineralised water:

20230204_105956.jpg - 2.1MB

20230204_110346.jpg - 2.3MB

I'm not sure what the exact solubility of FeSO4.H2O is at room temperature, but Wikipedia cites 29.5 g/100 mL for the heptahydrate and 44.7 g/100 mL at 70 deg C. Either way, it's nowhere near the level which should result in a milky solution when dissolved at <1g/100mL. I've experimented a bit and produced very similar results when adding citric or ascorbic acid.

To expand on what I meant by the fertilizer analysis looked weird: the fertilizer claimed to be 28% Fe, 11.5% S by weight. However, ferrous sulphate monohydrate is 32.9% Fe, 18.9% S by weight. The two ratios don't match up (28/32.9 = 0.851, 11.5/18.9 = 0.608), and they're both off the 90%-100% purity claimed by the manufacturer. Curiously though the 28% Fe would match if the chemical was ferric sulphate ((55.85 * 2)/399.88 = 27.9%) while the 11.5% S would match if the chemical was ferrous sulphate heptahydrate; in any case I have no idea how they came up with the claimed w/w estimates.

Anyways, that's a really long-winded way of noting that the SDS/nutrient analysis provided by companies shouldn't always be trusted. The products are often packed and stored in conditions which are fine for whatever their end-use is, but which can render them impure.

maldi-tof - 11-2-2023 at 00:34

Quote: Originally posted by KoiosPhoebus  
Quote: Originally posted by Chemgineer  
Also worth searching for an MSDS material safety datasheet for your particular brand of fertilizer, that should give you details of the active ingredients.


Agreed, that can often be quite helpful but is sometimes misleading, intentionally or otherwise. For example, a bottle of iron sulfate fertilizer I bought recently which was supposed to be iron (II) sulfate monohydrate (>90% purity). However, the nutrient analysis was really weird - the % iron was more similar to that of iron (III) sulfate monohydrate while the % sulfur was more similar to that of iron (II) sulfate monohydrate. When I finally got around to using it, it formed a yellow solution and was only somewhat soluble - ferrous sulfate is supposed to produce green solutions and is highly soluble. My guess is that maybe the iron (II) sulfate monohydrate oxidised to various ferric salts, or the company actually blended ferric salts into the fertiliser to get a higher iron content.

Additionally, I recently picked up a fertilizer which claimed to be 17-0-0 calcium nitrate and whose SDS claimed it was calcium nitrate, not the double salt calcium ammonium nitrate. However, when I tested it for ammonia using an aquarium NH3 test and compared it to an equal mass of 15.5-0-0 CAN, it had the same amount of ammonia as the double salt. So SDSes can definitely be useful, but a lot of the time, fertilizers are repacked and resold by distributors who may not know a lot about the chemistry of what they're selling.


Iron (ii) sulphate 7-hydrate is quite soluble, you can have a solution of 30% p/p easily. It will be very dark green if the iron (iii) content is low.

However, iron (ii) sulphate monohydrate is almost insoluble in water. The monohydrate can be obtained by acidifying with some sulphuric acid a solution of iron (ii) sulphate 7-hydrate, and bring that solution to boil. After a while, you will get a precipiate which is the monohydrate. Getting rid of this monohydrate requieres a loooot of water and heat as well.

The colour/shape of the crystals of the 7-hydrate and monohydrate are very different. The 7-hydrate usually is pale green, and the crystals usually are well formed. However, for the monohydrate, as normally it precipitates, is more common to obtain a powder rather than crystals.

In order to conclude, you can always test the content of iron (ii) in iron (iii) salts and viceversa using; a salt of thiocyanide and check for red colour (test of iron (iii)) and ferricianide for checking iron (ii) in iron (iii) salts.

KoiosPhoebus - 17-2-2023 at 20:29

Quote: Originally posted by maldi-tof  
Quote: Originally posted by KoiosPhoebus  
Quote: Originally posted by Chemgineer  
Also worth searching for an MSDS material safety datasheet for your particular brand of fertilizer, that should give you details of the active ingredients.


Agreed, that can often be quite helpful but is sometimes misleading, intentionally or otherwise. For example, a bottle of iron sulfate fertilizer I bought recently which was supposed to be iron (II) sulfate monohydrate (>90% purity). However, the nutrient analysis was really weird - the % iron was more similar to that of iron (III) sulfate monohydrate while the % sulfur was more similar to that of iron (II) sulfate monohydrate. When I finally got around to using it, it formed a yellow solution and was only somewhat soluble - ferrous sulfate is supposed to produce green solutions and is highly soluble. My guess is that maybe the iron (II) sulfate monohydrate oxidised to various ferric salts, or the company actually blended ferric salts into the fertiliser to get a higher iron content.

Additionally, I recently picked up a fertilizer which claimed to be 17-0-0 calcium nitrate and whose SDS claimed it was calcium nitrate, not the double salt calcium ammonium nitrate. However, when I tested it for ammonia using an aquarium NH3 test and compared it to an equal mass of 15.5-0-0 CAN, it had the same amount of ammonia as the double salt. So SDSes can definitely be useful, but a lot of the time, fertilizers are repacked and resold by distributors who may not know a lot about the chemistry of what they're selling.


Iron (ii) sulphate 7-hydrate is quite soluble, you can have a solution of 30% p/p easily. It will be very dark green if the iron (iii) content is low.

However, iron (ii) sulphate monohydrate is almost insoluble in water. The monohydrate can be obtained by acidifying with some sulphuric acid a solution of iron (ii) sulphate 7-hydrate, and bring that solution to boil. After a while, you will get a precipiate which is the monohydrate. Getting rid of this monohydrate requieres a loooot of water and heat as well.

The colour/shape of the crystals of the 7-hydrate and monohydrate are very different. The 7-hydrate usually is pale green, and the crystals usually are well formed. However, for the monohydrate, as normally it precipitates, is more common to obtain a powder rather than crystals.

In order to conclude, you can always test the content of iron (ii) in iron (iii) salts and viceversa using; a salt of thiocyanide and check for red colour (test of iron (iii)) and ferricianide for checking iron (ii) in iron (iii) salts.


Thanks for that info. I'm surprised that ferrous sulphate monohydrate is so minimally soluble - do you have a source or some other info on this?

Additionally, is the solution of the monohydrate supposed to be yellow? Because that's the colour I get when I add the "iron sulphate" into water.

The other reason I'm suspicious of the "ferrous sulphate monohydrate" I was sold is because of the declared nutrient analysis. The reply above yours has more detail, but TLDR the declared % iron and % sulphur both don't make sense if the product was really ferrous sulphate monohydrate; even if we're talking about an impure product, the iron:sulphur ratio is much higher than it should be for any iron (II) sulphate.