Oxalic Acid Strength

[Worker Dave]

Oxalic Acid Strength

I see that the current advice is to use 3.2% OA. I purchased 4.5% and duly watered it down. Today I have been to a demo at Wally Shaw’s and he informed me that I shouldn’t have done so. I am posting to let people know that if they have the 4.5% solution to not water it down. The following I do not profess to understand but is the explanation I was given.

The confusion about the strength of OA arises from there being two different methods to express it. From a chemical point of view it is normal to express it as the strength of the acid. But because OA can only be purchased as a raw material to then make up solutions in its dihydrate form, it is the strength of the solution of OA as the dihydrate (OAD) that is more normally used in beekeeping.
The chemical formula for OA is C2O4H2 giving a molecular weight of 90 (2 x 12 plus 4 x 16 plus 2 x 1= 90) The dihydrate part is a water of crystallisation involving 2 molecules of water (2 x H2O) per molecule of OA and this increases the molecular weight of the dehydrate to 126 (2 x 16 plus 4 x 1 =36). So to convert from the concentration of OA to that of OAD you multiply by 1.4
As I say I don’t profess to understand the chemistry but the bottom line is your 4.5% solution shouldn’t be watered down
Cheers Dave

 

[Repwoc]

I agree it is confusing; however I think the prescribed recipe for beekeeping is 3.2% w/w (weight/weight) of OA dihydrate in 1:1 sugar syrup - this is what has been reported in the literature (many links can be found in other postings on this forum).

From my chemistry days solutions are generally specified in molarity or w/v (weight/volume). Sugar syrup is more dense than water. A 1:1 syrup made from 1 litre water and 1 kg sugar will weigh 2kg but the volume will be ~1.6 litres. So 4.5% w/v is equivalent to ~3.6% w/w.

So it is important to know the nature of the OA (dihydrate or anhydrous) but also if you obtain it in solution to be sure of the basis of the strength calculation ie w/w or w/v.

 

[jezd]

Yes, 71.4% of oxalic acid di-hydrate is oxalic acid, so using 4.5% of that has an end result of being 3.2% OA.

JD

 

[Finman]

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Oxalic Acid Strength
As I say I don’t profess to understand the chemistry but the bottom line is your 4.5% solution shouldn’t be watered down
Cheers Dave

The basic formula is for 3-5 hives 100 g wayter + 100g sugar +7,5 g OA.
You need not think it over. Just trust that it is correct.

Switherland uses 2,5% and Italya sometimes 4%. So there is some tolerance how exact it need to be.

And it is always weight %.

It is good to measure the water too with balance.

Sugar content is important too and so, don't add water, but 1:1 syrup.

Sugar glue the acid on bees' skin and the content has a great value in trefficacy.

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