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I have a small problem while reading Inorganic Chemistry Reference book.

The book stated that "In laboratory, Mn(II) hydroxide was prepared by the reaction of Mn(II) salt with alkaline in hydrogen atmosphere"

I guess the hydrogen atmosphere was to avoid Mn(II) being oxidised to Mn(III). Could it be nitrogen gas or other inert gases?

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  • $\begingroup$ Possibly yes: chemistry.stackexchange.com/a/165867/17368, chemistry.stackexchange.com/questions/165889/… $\endgroup$
    – Nilay Ghosh
    Commented Dec 16, 2023 at 4:53
  • $\begingroup$ I was also thinking that hydrogen gas could act as reducing agent in this case. Nitrogen, on the other hand, is way more inert to act as reducing agent. I wonder whether this explanation contributing to the usage of H2 atmosphere. $\endgroup$
    – Shira
    Commented Dec 16, 2023 at 8:07
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    $\begingroup$ Look up the Winkler method to measure dissolved O2 in water. In base MnII is oxidized by O2 to MnIII. The O2 could probably be removed by addition of a pinch of bicarbonate to an acidified solution, purging the CO2 with N2 or argon, and degassing the hydroxide. Alternatively react Mn with HCl maintaining a hydrogen atmosphere and neutralize with degassed hydroxide. $\endgroup$
    – jimchmst
    Commented Dec 16, 2023 at 8:53
  • $\begingroup$ The described method using hydrogen was published in Z. anorg. allg. Chem. 1937, 232(4), 369–381 and modified in J. Am. Chem. Soc. 1950, 72, 2, 856–866. $\endgroup$
    – Loong
    Commented Dec 16, 2023 at 16:34
  • $\begingroup$ @jimchmst I'm pretty sure it's oxidised to MnO2 - Mn(IV) not III. $\endgroup$
    – Mithoron
    Commented Dec 16, 2023 at 22:33

1 Answer 1

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Nitrogen would work if it were pure. In the real case it may contain traces of air/oxygen, or pick up this impurity as it is being delivered, and Mn(II) could be sensitive to that. Also the solution may carry air if it has be exposed to said air.

In steel processing applications a mixture of nitrogen with 5% hydrogen is often used, especially for heat treating, with the added hydrogen serving as a "buffer" against air or moisture impurity.

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