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Topic: accidentally precipitated CuSO4.5H2O & Na2MoO4.2H2O  (Read 3786 times)

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Offline scfalconry

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accidentally precipitated CuSO4.5H2O & Na2MoO4.2H2O
« on: July 15, 2014, 10:39:41 PM »
New to the forums... I have no formal education in chemistry.

My son and I are mixing our own hydroponic nutrients.  Our recipe required 0.031g of Sodium Molybdate (as a micro nutrient).

 To make dispensing the precise amount easier we mixed 3.1g of Sodium Molybdate into 500mL of water.   Allowing us to draw out 5mL that contained the total of 0.031g ingredient that we needed.

Since we also needed a very small amount (0.11g ) of Copper Sulphate... I suggested we mix 11g of copper sulphate into the same 500mL of water containing the sodium molybdate.

It immediately precipitated into a light green sludge of small crystals that will slowly settle to the bottom.    What is the name of this new crystal?  I wanted to look up the solubility of it... so I would use the minimum amount of water to use next time to prevent accidentally making it again.

Thanks in advance,
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Offline Ben Bob2

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Re: accidentally precipitated CuSO4.5H2O & Na2MoO4.2H2O
« Reply #1 on: July 16, 2014, 04:14:41 AM »
Could the copper cations from the copper sulfate have bonded with the hydroxide anions in the solution?
This would form copper hydroxide, an insoluble, blue precipitate, correct? 

If I'm way off, hopefully someone with a better understanding will correct me.
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Offline Arkcon

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Re: accidentally precipitated CuSO4.5H2O & Na2MoO4.2H2O
« Reply #2 on: July 16, 2014, 05:25:50 AM »
This is a common problem with DIY hydroponics.  You can't mix all the concentrated nutrients together (or even  few sometimes), and then dilute.  They will simply precipitate.  You have to break up your solutions into two or more groups, and inject concentrates into the water at separate times with plain water between.  They may stay soluble in the very dilute solution plants need, or the fine precipitate may cling to plant roots and be absorbed that way.  But that works better in soil.
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Offline scfalconry

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Re: accidentally precipitated CuSO4.5H2O & Na2MoO4.2H2O
« Reply #3 on: July 16, 2014, 07:28:16 AM »
Thanks for the replies.   I guess that is what I needed to know.... the Copper Molybdate Hydroxide that I accidentally made is insoluble.  I was hoping it was recoverable for use as plant nutrient.   The sodium molybdate cost me quite a bit for just a few ounces.... however no more than I use per mix... it will likely last me years!  :)   I was hoping that if I increased the volume of water to 1 liter... maybe it wouldn't precipitate next time... and I could have my three smallest ingredients all in the same solution.

I knew about keeping the calcium nitrate and sulfates separate at my regular concentration.  Was unaware that the Copper Sulfate and Sodium Molybdate would also be a problem . however I was dumping a lot more of each, into a smaller amount of water than I normally mix up.

FWIW... My 100x concentrate, 2 part recipe, hydroponic nutrient recipe for any who are intersted:
It creates 204 liters of working solution for the hydropinc reservoir.

Part A...   I normally mix 2 liters of water with:
Calcium Nitrate MBF (Tetrahydrate)   Ca(NO3)2.4H2O   296g
Potassium Nitrate MBF   KNO3   179g
Iron EDTA   Fe(EDTA)   4g
For Part B..   I  mix 2 liters of water with:
Magnesium Sulfate (Heptahydrate)   MgSO4.7H2O   91g
Phosphoric Acid (85%)   H3PO4   49g
Manganese Sulfate (Monohydrate)   MnSO4.H2O    0.492g
Boric Acid   H3BO3   0.343g
Zinc Sulfate (Dihydrate) 35%   ZnSO4.2H2O   0.057g
Copper Sulfate (pentahydrate)   CuSO4.5H2O   0.055g
Sodium Molybdate (Dihydrate) 39.5%   Na2MoO4.2H2O   0.015g

To make the Zinc Sulfate, Copper Sulfate and Sodium Molybdate easier to measure..  I'm thinking I will make a solution of each individually... so that as I need to add them... I can just draw up a few mL in a syringe.  Thanks for helping point the newbie in the right direction.

Thank you,
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