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KCL won't dissolve

eminor

Member
Joined
5 Feb 2021
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792
Location
France
Hello, i try to dissolve KCL in water, 26g of KCL in 210 ml of water at room temperature, i don't know why but the powder stay in the bottom, can i try to heat up the solution to fix it ? thx
 
Did you get it from a reputable source?
KCl should dissolve readily, my first thought would be to suspect that it's not KCl.
Yes, from a factory that make it directly, yes if i remember my schools years, KCL is highly soluble
 
KCL is highly soluble
As mentioned 26g should dissolve in 210ml of water. Here's a snap shot of solubility levels in g/per 100ml of water @ 0,20 & 40 ⁰c.
Screenshot_20220821-100223_Chrome.jpg


I would imagine these solubility levels are tested using pure water and not any old tap water but you shouldn't really have any issues with the numbers you're working with.
 
@eminor instead of 26g of KCL in 210 ml of water, does this dissolve fully if you were to add 5 gram ? if it fully dissolve then try adding the following to it after fully dissolving it:

10 gram Calcium Nitrate
or
10 gram Calcium Chloride

if its truly KCL. there wont be any reaction or Precipitation, if Precipitation occurs then you likely have K2SO4, not KCL. its also less likely that you have KHCO3 or K2CO3 because both are also highly soluble, but they too will react in similar way if you were to add Calcium Nitrate or Calcium Chloride to your solution, except they will form CaCO3 instead of the CaSO4. this could be a simple test to see if you truly have KCL or not. it might very well be K2SO4 which wont fully dissolve with the above 26 gram into 210 ml
 
As already mentioned was the water pure water RO or DI water?
Plus had any other salts already been added ? as if you had already added any SO4 or CO3 the undissolved salt may be due to the command ion effect as mentioned by @Happi
 
hey guys thanks for the answers, it was distilled water, the powder was faulty, it was k2so4, i don't want it because it boost diatoms growth already in huge amount in my tap
 
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How? What?
I think he is confusing silicates with sulphate? Anyway, I would highly recommend using k2so4 since kcl is a very alkaline chemical. And some people have reported issues, no such issues with k2so4 however.
The link between silicates and diatoms is pretty fuzzy imo, I wouldn’t recommend fretting about silicate levels.
 
I would highly recommend using k2so4 since kcl is a very alkaline chemical
pH of 1 mM solution: K2SO4 7.01, KCl 7.00. No difference, really. (Taken from CRC Handbook of Chemistry and Physics 90th ed [internet ed] - D. Lide (CRC, 2010) WW, a highly authoritative source.)
 
pH of 1 mM solution: K2SO4 7.01, KCl 7.00. No difference, really. (Taken from CRC Handbook of Chemistry and Physics 90th ed [internet ed] - D. Lide (CRC, 2010) WW, a highly authoritative source.)
Hmmm, I wonder why I thought kcl was much more alkaline. Apologies🙃 and will edit my comment.
 
Hi all,
pH of 1 mM solution: K2SO4 7.01, KCl 7.00. No difference, really. (Taken from CRC Handbook of Chemistry and Physics 90th ed
What @_Maq_ says.
Hmmm, I wonder why I thought kcl was much more alkaline
Potassium (K) is an alkaline metal, but potassium chloride (KCl) is a <"neutral salt">, because it is formed from the reaction of a strong acid and a strong base.
@X3NiTH is right, potassium chloride (KCl) is a <"neutral salt"> because is the product of the reaction between a strong base (KOH) and a strong acid (HCl). Potassium (K) is a <"group one alkali metal">. Group 1 metals are highly reactive and only occur as compounds (salts), <"those salts are all soluble">.
I should have put the reaction in for K2SO4 as well.
......... potassium sulphate(K2SO4) is the salt formed by combining KOH (potassium hydroxide) and H2SO4 (sulphuric acid). Because H2SO4 is a strong acid, and KOH is a strong base, K2SO4 is a neutral salt.......

cheers Darrel
 
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Hello, i have another issue with mixing dry ferts, KNO3 here, 100% certain that it's KNO3 this time

I used bleach to kill any living things in a 240 ml brown glass bottle, i then used really hot water to clean the bottle, i dried it. Then, I added demineralised water to remove any ions, i removed the demineralised water, added 9g of KNO3 powder, added 200ml of demineralised water, and finally i've shaked the bottle to mix everything.

Problem is that there is still some powder in the bottom of the bottle if i let it rest, if i shake it well before dosing, does the calculation is still correct without 100% mix ?

i know that KNO3 is not perfectly soluble in room temperature, but if i mix it in hot water there will be evaporation which will make the calculation wrong ? thx
 
Hi all,
i know that KNO3 is not perfectly soluble in room temperature
It is <"pretty soluble">, via <"Wikipedia">: "316 g/1000 g water (20 °C)". In fact ~all potassium and nitrate containing compounds are soluble. So it must be a contaminant.
Problem is that there is still some powder in the bottom of the bottle if i let it rest, if i shake it well before dosing, does the calculation is still correct without 100% mix ?
It should be all right, it won't be exactly the dose that you want, but it should be close enough. The reason for "close enough" is that
removed the demineralised water, added 9g of KNO3 powder, added 200ml of demineralised water
Would have meant that your original solution was more less concentrated than you thought. You should have added the DI water to the KNO3 powder until it weighed 200g, yours will have weighed ~209g, if that makes sense?

cheers Darrel
 
Hi all,

It is <"pretty soluble">, via <"Wikipedia">: "316 g/1000 g water (20 °C)". In fact ~all potassium and nitrate containing compounds are soluble. So it must be a contaminant.
Damn, i don't know how it came in
It should be all right, it won't be exactly the dose that you want, but it should be close enough. The reason for "close enough" is that

Would have meant that your original solution was more less concentrated than you thought. You should have added the DI water to the KNO3 powder until it weighed 200g, yours will have weighed ~209g, if that makes sense?
Well i added the 9g kno3, pressed tare then added 200ml of di water, so yeah 209g, should've added 191g of water instead ?

Pump is 1.5 ml, 200 ml, 9g kno3, 45 liters, which mean that i put 0.92 ppm for each press, instead of 0.96 ppm NO3 with 191g of water, if i'm using the calculator well, it might be ok ?

I wanted 1 ppm, but i have no kno3 left for the moment
 
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Hi all,
Well i added the 9g kno3, pressed tare then added 200ml of di water, so yeah 209g, should've added 191g of water instead ?
Yes.
Pump is 1.5 ml, 200 ml, 9g kno3, 45 liters, which mean that i put 0.92 ppm for each press, instead of 0.96 ppm NO3 with 191g of water, if i'm using the calculator well, it might be ok ?
It will be fine. I'm <"not too worried"> about the <"minutiae of dosing">.

cheers Darrel
 
I don't know exactly why, but everytime i dosed k2so4 i had diatoms in my tap water aquariums, if i dose KCL, i don't have diatoms
Hi @eminor

Diatoms require silica, sulphur and carbonate. So, when you were dosing potassium sulphate (K2SO4), you would have been adding sulphur to your tank. When dosing potassium chloride (KCl), sulphur would not be present. You may find the following scientific paper to be of interest. But, I don't recommend it for bedtime reading as it is quite detailed. Here it is:


JPC
 
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