is this K2SO4? - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 06-06-2015, 06:06 PM Thread Starter
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is this K2SO4?

I have a question, I have two bags of k2so4 that i've had for a year or two. One bought from GLA and one from Bobs tropical plants.

The GLA bag has a crystal salt consistency like my kh2po4/kno3.

The bobs tropical plants bag has a powder consistency, like flour.

Could they both be k2so4? or is one something else?

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post #2 of 12 (permalink) Old 06-06-2015, 10:43 PM
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I've bought K2SO4 from a couple of places here - it has a dry, dull, powdery consistency, and has what seems to be tiny black flecks of some sort of insoluble contaminant.....
My KNO3 and KH2PO4 are more crystalline, and the KNO3 clumps together readily.
Saying that, I bought 3kg of AR grade KNO3 for a good price recently, and it seems to have been granulated into little spheres, maybe 1-2mm diameter, I suspect to stop it clumping......
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post #3 of 12 (permalink) Old 06-06-2015, 11:13 PM
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Quote:
Originally Posted by HolyAngel View Post
I have a question, I have two bags of k2so4 that i've had for a year or two. One bought from GLA and one from Bobs tropical plants.



The GLA bag has a crystal salt consistency like my kh2po4/kno3.



The bobs tropical plants bag has a powder consistency, like flour.



Could they both be k2so4? or is one something else?

If you compare to kh2po4 and kno3, k2so4 is the most powder like, if in lab grade powder form.

Easy way to tell: put 1/20 tsp in a test vial and test separately for nitrate and phosphate content.
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post #4 of 12 (permalink) Old 06-06-2015, 11:14 PM
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Quote:
Originally Posted by lee739 View Post
I've bought K2SO4 from a couple of places here - it has a dry, dull, powdery consistency, and has what seems to be tiny black flecks of some sort of insoluble contaminant.....
My KNO3 and KH2PO4 are more crystalline, and the KNO3 clumps together readily.
Saying that, I bought 3kg of AR grade KNO3 for a good price recently, and it seems to have been granulated into little spheres, maybe 1-2mm diameter, I suspect to stop it clumping......

Be careful, sounds like you have aggro grade granular, not lab grade powder form(hence less expensive). Some of these cause heat when dissolving, and some are NOT easily water soluble.
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post #5 of 12 (permalink) Old 06-06-2015, 11:23 PM
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The KNO3 came in sealed 1kg reagent canisters, from a chemical supplier, so I doubt it isn't AR grade. I haven't tried to dissolve it as yet though, but I make solutions, so decreased solubility wouldn't bother me too much....
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post #6 of 12 (permalink) Old 06-07-2015, 12:23 AM Thread Starter
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Quote:
Originally Posted by Xirxes View Post
If you compare to kh2po4 and kno3, k2so4 is the most powder like, if in lab grade powder form.

Easy way to tell: put 1/20 tsp in a test vial and test separately for nitrate and phosphate content.
Suppose I can test for nitrate but don't have a phosphate test kit and can't get one locally. May just have to order one anyways.

--

To all: Thanks for the info and clarification

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post #7 of 12 (permalink) Old 06-07-2015, 01:07 AM
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I'd say if your not sure buy some more its about 3 bucks a pound.


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post #8 of 12 (permalink) Old 06-07-2015, 03:14 AM
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If you do not want to buy a phosphorus test, then find a store locally that will test it for you. A little bit goes a LONG way, so a tiny pinch in a vial of water will show positive, if it is a phosphorus fertilizer.
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post #9 of 12 (permalink) Old 06-07-2015, 03:46 AM
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A solution of KH2PO4 is acidic, pH around 4. The others should be neutral. This may help distinguish them too.
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post #10 of 12 (permalink) Old 06-07-2015, 04:17 AM Thread Starter
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Oh nice! didn't know that. And I only have pet smart/Petco here, no proper LFS, so I'll have to either go with the pH method or buy a phos test kit.

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post #11 of 12 (permalink) Old 06-07-2015, 12:31 PM
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I had this experience with GLA too. I have found a few other forum members that have found the same problems. First off I'd contact GLA customer service, I was assured I was the only one with this issue but clearly im not. The way I was able to prove it was in fact KN03 was by making a solution with it to generate 40ppm of nitrate, then once mixed confirmed with a test kit.

GLA says K2So4 has a slight odor to it where as KNo3 does not. Please contact their customer service, I really do think they are mixing up their bags and do not know.
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post #12 of 12 (permalink) Old 06-07-2015, 01:32 PM
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The consistency of a purchased chemical rarely has anything to do with its purity or identity. If you've synthesized it, then it will form characteristic crystals, but we're buying processed products, and they are milled to whatever consistency the manufacturer chooses.

If you suspect that one of them isn't potassium sulfate, then there's no good reason to suppose that it's anything else in particular. There are a few relatively simple things you can try to identify it, but by and large you've just got mystery powder.

Things to try:
1. Flame test: You probably did this one in chemistry class. Dissolve a small amount of the salt in an alcohol/water mixture, then use a small loop of wire with a long handle (like a bubble wand, but with a tiny bubble blowing end) to scoop a bit out. Darken the room and hold it over a hot flame (blow torch or kitchen stove preferably, a lighter, candle, or match if you're really desperate) and look for colors in the flame. This is a less than ideal setup, and potassium flame tests are fairly weak, but if it contains potassium you should be able to see lavender in the flames. You may also get a whiff of sulfur at this point and solve the mystery entirely.

2. Selective precipitation:
Do you have any soluble calcium and/or magnesium salts (CaCl2, for hardness adjustments or as ice melt salt, for instance? Epsom salt?) If so, mix a solution of calcium salt with a solution of the K2SO4. If nothing happens, it's not sulfate or phosphate. Try a solution of magnesium salt. If nothing happens it's not phosphate. There are a billion other things it could be, but if we're limiting ourselves to sulfate/phosphate/nitrate, then that tells you which is which.

3. Reactivity:
Potassium nitrate is a strong oxidizer. If you have common sense and a safe place to do this, mix equal amounts of sugar and mystery salt, place it outside on a non-flammable surface, and light it on fire with a blowtorch. (You can use matches or a lighter, but it's more difficult to get started and you risk burnt fingers.) If it's KNO3, it will burn completely and brightly, producing lots of white smoke. If it's sulfate or phosphate, you'll look ridiculous in your driveway.
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