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Dissolving salicylic acid

I'm not a chemist but am trying to make a product to be used as a foliar spray on turfgrass for my own use. The product I'm trying to make is:

12% Humic Acid (pH 3.5-4.0)

2% Fulvic Acid (pH 9.6)

6% Kelp Extract

0.5%Salicylic Acid

79.5% Water (local sourced water pH is 6.8-7.5)

I'd like to make this in 19L (5 gal.) batches.

The humic, fulvic and kelp are all soluble or in solution already, so that's the easy part. What I'm looking for advice for is how to dissolve the salicylic acid so that it can be combined with the other ingredients.

The advice I've been given for dissolving the salicylic acid is to first dissolve in ethanol. Add KOH to water until I get a pH of 12, then add the dissolved salicylic acid to the water.

What I'd like to know is:

1. Is this the right process?

2. What quantities of salicylic acid/ethanol/KOH/water should I be using?

3. Will adding this mixture to my mixture of humic/fulvic/kelp have any negative effect on any of the ingredients?

4. Any safety concerns beyond the KOH exothermic reaction?


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3 Replies
New Contributor

Re: Dissolving salicylic acid

That will work but it is needlessly complicated. Since salicylic acid is not soluble enough in water at room temperature to achieve your desired composition, it must be converted to salicylate. This can be done by reaction of sodium bicarbonate (baking soda) with salicylic acid in water - the salicylic acid will dissolve as it reacts. Add sodium bicarbonate slowly to a stirred suspension of salicylic acid so that the bubbling of carbon dioxide is not too vigorous. Sodium salicylate is very soluble in water so you can use a sufficiently small amount of water to not complicate the preparation of your final mixture.

Re: Dissolving salicylic acid

Greg, the real question is what the final pH of your solution will be.  If combining all the other ingredients results in a pH around 7, then the salicylic acid will dissolve as it is converted to the salicylate salt.  If the pH is 4 or lower, the salicylic acid will not dissolve completely (its pKa is 2.97 according to Wikipedia— that’s the pH where half of the salicylic acid is ionized to salicylate).  Water has little or no effect on the final pH, it depends on the other ingredients and their acidic or basic components. If you need to raise the pH, KOH sounds like a good choice since potassium is good for plants. 

New Contributor

Re: Dissolving salicylic acid

Thank you Allen. The studies used to show the effects of salicylic acid on turfgrass used pure salicylic acid dissolved in water. In your opinion, do you believe that salicylate would have the same effect?

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