RogueRose
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H2O2 ratio needed to dissolve metals in acid - 2:1 ratio or more?
So I've experienced something odd on a few occasions when dissolving metals (Cu, Ni, SS) in either HCl or H2SO4d at 31.4% & 32% respectively. My
H2O2 is 35%. I assumed that I would need approximately 2x the amount of H2O2 than acid but it seems to be working out to A LOT more, on the order of
8-12x the amount acid used. The dissolution has taken place at room temp and adding small amounts of H2O2 at a time to keep the reaction from running
away and to limit H2O2 decomp.
I calculated by volume which I'm now suspecting may have been a mistake. Is there a calculation I'm missing here? 2(H2O2) = 2(H2O) + O2 is how I
figures I'd need 2x the amount.
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DavidJR
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Volume ratio isn't really what's relevant though, the molar ratio is.
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LearnedAmateur
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Yeah, think about it - if you have 35% or 3% H2O2 you can’t just use the same volume for either since they’re different concentrations; even for
100% pure reagents you still need to figure out how many moles you have present. H2O2 has a molecular mass of 34.01g/mol and the pure density is
1.45g/mL.
If by weight, 35% peroxide has a concentration of 10.3M or 1.03 mol/100mL. If by volume, there are 50.75g/100mL (35mL * 1.45) so the concentration is
14.5M, 1.45 mol/100mL. It should say somewhere which one it is, denoted by w/w and v/v respectively.
In chemistry, sometimes the solution is the problem.
It’s been a while, but I’m not dead! Updated 7/1/2020. Shout out to Aga, we got along well.
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Deathunter88
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H2O2 decomposes upon exposure to transition metal ions, and can also decompose from impurities/heat generated by the reaction. So you need a lot more
H2O2 than theoretical.
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