I have several ground up soil samples that I need to get fractions from. The fractions are based on the Century Soil Model. Briefly, the fractions relate to the approximate time frame it takes for an organic carbon pool to be metabolized in the soil. Fast pools ≈1 year, slow pools ≈10+ years, etc.

I have looked at several papers to try to get an idea of the chemical methods used for digesting the soil samples to get at the more stable carbon pools. For more easily digested organic carbon pools, hot water seems to work, but for the middling and more recalcitrant pools, other reagents are used.

Some methods mentioned include:

  • dissolve in $\pu{0.1 M}~\ce{NaOH} + \pu{0.1 M} ~\ce{Na4P2O7}$
  • dissolve in $\ce{HCl}$
  • reflux with $\pu{6 M} ~\ce{HCl}$
  • "stepwise chemical digestion with cold and hot $\ce{H2SO4}$ (95 - 98% concentration)"
  • oxidation with $\ce{KMnO4}$ ($33\text{ or }\pu{333 mM}$) (this one I see mentioned most frequently)

I am not a chemist. I took the required chemistry classes for my degree and passed, but that's years ago now. When I did do chemistry labs, my results hardly ever came out as they were supposed to, so my skill in this field is minimal. Besides these methods not working, and thus wasting time and money, my real concern is how potentially dangerous these chemicals are. Would someone be so kind as to give me an indication of how risky these chemicals might be? We have a functioning fume hood, will buy PPE, and be sure there are safety procedures in place, but I'm still wondering how much I should worry if a flask breaks or something spills.


2 Answers 2


$\pu{0.1 M}~\ce{NaOH}$ is potentially corrosive when in contact with metals or human skin (see here), so I advise precautions such as wearing protective standard gloves and keep metals away from feasible damage.

$\ce{HCl}$ and $\ce{H2SO4}$, especially when they're hot and are in higher concentrations, are very corrosive acids that are dangerous in contact with many materials. They can also release noxious gases in the reactions, but their weakness is glass. Due to reasons irrelevant, these acids can't corrode glass. I recommend extreme precaution. You can work under a "glassy" protection and as Yomen mentions, under a fume hood. Gloves are very important here. Here's what Caltech thinks about precautions using $\ce{HCl}$ and here's what Berekley does about sulfuric acid.

$\ce{KMNO4}$ is a very strong oxidizer. It may cause fire in contact with different materials (we had a volcano experiment in elementary school where we mixed it with glycerine and the result was very exothermic), and it has biohazards such as kidney damage. Here it's explained more comprehensively.


You must be careful when working with hot and concentrated acid solutions as they are corrosive. Otherwise, the chemicals you mentioned are common ones.

Because you are not used to manipulate chemicals, I advise you to wear goggles and protective gloves while preparing solutions. Work under fume hood when refluxing $\ce{HCl}$.


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