Potassium nitrate NOT dissolving

8851 Views 12 Replies 9 Participants Last post by Diana, Nov 5, 2010

grshs_vny

Discussion Starter · Nov 1, 2010

Hi,I am trying to make stock solution for the first time and the potassium nitrate is not completely dissolving in water.I took 250 ml of water and added 212grams of lab grade potassium nitrate to it.At first 50% of solute dissolved and 50% remained at the bottom.I stirred it very well but certain amount is still there.I then warmed the solution using water bath and 70% of the solutes are dissolved but as the solution cooled to room temperature solutes are again crystalised. my room temperature is 23 deg. celcius.Today i even increased the solvent by 200 ml but no improvement

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Hoppy

· #2 · Nov 1, 2010

This is an easy problem to solve - just use less KNO3 and/or more water. :hihi:

Seriously, water won't dissolve an unlimited amount of anything, so you have to work within the solubility limits for what you are dissolving.

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OverStocked

· #3 · Nov 1, 2010

potassium nitrate has a solubility of about 22g in 100ml of water at room temp. 55g in 250ml(and this is really pushing it). You are trying to put 4 times this much.

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Darkblade48

· #4 · Nov 1, 2010

grshs_vny said:
I took 250 ml of water and added 212grams of lab grade potassium nitrate to it.

over_stocked said:
potassium nitrate has a solubility of about 22g in 100ml of water at room temp. 55g in 250ml(and this is really pushing it). You are trying to put 4 times this much.

As over_stocked mentioned, while solubility of KNO3 is high, it is not as high as you think it to be (212 grams of solute into 250 mL of water?!).

Depending on the temperature, the solubility of KNO3 is about 36 grams per 100 mL of water (this is at 25C).

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OverStocked

· #5 · Nov 1, 2010

While it is supposed to be able to dissolve 36g/100ml, it is actually rather difficult. Even in distilled water. IT is definitely not stable in solution at this level.

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Hoppy

· #6 · Nov 1, 2010

That instability is why it is bad idea to try to saturate the water with any of the fertilizers. If the temperature drops it comes out of solution. Any drips of it come out of solution very quickly. If any water evaporates, it comes out of solution. There is really no reason to try for such concentrated solutions.

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Sharkfood

· #7 · Nov 2, 2010

I just dump it straight into my tank. Much easier IMO.

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barbarossa4122

· #8 · Nov 2, 2010

I tried 125 gr in 500ml water and it did not work too well. Now, I am doing 80 gr in 500ml.

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grshs_vny

Discussion Starter · #9 · Nov 3, 2010

Sorry guys it all happened coz of CHUKK'S calculator.It says you can dissolve around 85grams per 100ml of water.:icon_conf

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Darkblade48

· #10 · Nov 3, 2010

grshs_vny said:
Sorry guys it all happened coz of CHUKK'S calculator.It says you can dissolve around 85grams per 100ml of water.:icon_conf

The program is a little outdated.

Always best to double check your sources/references

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mistergreen

· #11 · Nov 3, 2010

chuck's calculator is good but it doesn't account for solubility.

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wet

· #12 · Nov 4, 2010

Just for you, grshs_vny. (And a standing request from tug

)

It'll send that alert in red when you're 80% of the solubility (or higher) for KNO3, KH2PO4, KCl, K2SO4, CaCl2.2H2O, CaSO4.1/2H2O, CaSO4.2H2O, MgSO4.7H2O, or MnSO4.H2O, measured at "room temperature." (20 - 25 C, depending on what I could find.) A compromise to the points above and standardization for the purposes of building this calculator.

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Diana

· #13 · Nov 5, 2010

What are you aiming for with so strong a solution?

Better, as already noted, to add less fertilizer or more water. Make a weaker solution, then dose more to get the same amount of active ingredient.
Especially if you are mixing several of the macros in one blend. Keep all of them well under the saturation point.

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