[benjamingrantdu]

Hi All,
I'm a little confused by a paper I'm trying to replicate. They say they use "enough sodium percarbonate to produce .025% H202 in water".  I assume they mean weight/volume.  The confusing part to me is when buying sodium percarbonate, it's specified as "avail. H2O2 20-30 %".  I'm not sure how that comes into play or where that number comes from.

This is how I proceeded, if I'm off in my methods, could you please let me know?

I am making 100 mL and want .025% H202.

The mass I need is thus .00025 g/mL * 100 mL = .025 g H202.

Converting that to moles, .025g/34.0147 g/mol = 1.041 x10^-3 mol H202

The reaction for producing H202 from sodium percarbonate is:
2Na₂CO₃·3H₂O₂  2Na₂CO₃ + 3H₂O₂

Therefore I need 2/3 *1.041 * x 10 ^-3 mol sodium percarbonate or 6.94 x 10 ^-4 mol sodium percarbonate

That's .095 g of sodium percarbonate, or 95 mg.

I was going to say since worst case scenario is that only 20% of the sodium percarbonate is available for production of H202, that I then just divide by 0.2, yielding 475 mg.  Does this seem right or am I completely missing something?

Thanks

[discodermolide]

I think that figure refers to the amount of H₂O₂ that can be generated from the stuff in the bottle.
20-30% is quite a wide range, in my opinion.
So I would titrate the stuff to get a more accurate value, especially if you are using sensitive starting materials, or want to use the least amount possible for your reaction.

[benjamingrantdu]

I think that figure refers to the amount of H₂O₂ that can be generated from the stuff in the bottle.
20-30% is quite a wide range, in my opinion.
So I would titrate the stuff to get a more accurate value, especially if you are using sensitive starting materials, or want to use the least amount possible for your reaction.

I agree it's a pretty wide range, I'm using it for a chromogenic reaction with DAB where H202 should be the excess reagent so it's not a huge problem for me to err on the side of too much

[discodermolide]

Why not use hydrogen peroxide itself?

[benjamingrantdu]

Why not use hydrogen peroxide itself?

it's for a lateral flow assay in which all the reagents are pre-dried on the lateral flow strip so that the end user just adds water and the patient sample to run the test. The 100 mL I provided in the question was just an example to see if I was calculating the percent h202 correctly -- but the idea is to have a dry, stable source of H202.