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I know sodium metal, when reacted with water, produces flammable hydrogen gas but I was wondering if that would also be the case if I had aqueous 1M sodium hydroxide?

Would this reaction be safe or will it also produce a harmful compound like hydrogen gas?

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    $\begingroup$ Yes, the sodium metal will react with the water to produce more sodium hydroxide and hydrogen (gas)... until there is no water left to react with. $\endgroup$
    – Ben Welborn
    Aug 12, 2016 at 18:42
  • $\begingroup$ ok, so will the sodium metal be consumed? And how fast would that be? $\endgroup$
    – user510
    Aug 13, 2016 at 3:45
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    $\begingroup$ 1M aqueous sodium hydroxide is no different from water in this regard. $\endgroup$
    – Ivan Neretin
    Aug 13, 2016 at 8:49
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    $\begingroup$ Follow up question that (to me at least) is slightly less easy to answer: what if you react molten sodium metal with molten "anhydrous" sodium hydroxide? Do you get sodium oxide and hydrogen? $\endgroup$
    – Curt F.
    Jan 6, 2017 at 20:32

2 Answers 2

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Consider first the solvation of sodium metal in water to give a sodium ion and a hydrated electron.

$$\ce{Na(s) \xrightarrow{\ce{H_2O}} Na^+(aq) + e^-(aq) }$$

The hydrated electron will then act as the reactive species to reduce water to hydrogen atoms and hydroxide anions.

$$\ce{e^-(aq) + H_2O(l) \rightarrow H(aq) + OH^-(aq)}$$

Note that two of these hydrogens come together to form the diatomic hydrogen gas.

$$\ce{2H(aq) \rightarrow H_2(g)}$$

When we multiply the coefficients in the first two equations by two, we are able to consider the net ionic equation through the elimination of the reactive intermediates.

$$\ce{2Na(s) + 2H_2O(l) \rightarrow 2Na^+(aq) + 2OH^-(aq) + H_2(g)}$$

We see that the dissolution of sodium metal in aqueous sodium hydroxide would be affected by Le Chatelier's principle due to the presence of the sodium hydroxide. We would expect there to be a reduction of solubility and rate of dissolution. The greater the initial concentration of sodium hydroxide, the more appreciable the effect.
Given that a solution of sodium hydroxide at $\ce{25 ^{\circ}C}$ is saturated at $\ce{25 M}$, a $\ce{1 M}$ solution would not be expected to have an appreciable effect. Hydrogen gas would remain a product, evidenced by the net equation.

As far as the reaction of molten sodium and molten sodium hydroxide, I expect that is what they were referring to on the Wiki page for sodium oxide when they gave this equation.

$$\ce{2NaOH + 2Na \rightarrow 2Na_2O + H_2}$$

The source given is Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
The solubility of sodium hydroxide was resourced from the Wiki page for sodium hydroxide. The source given appears to be Haynes, CRC Handbook of Chemistry and Physics.
The first set of equations were sourced from Walker, David C. Production of Hydrated Electrons. Canadian Journal of Chemistry. Volume 44. 1966.

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  • $\begingroup$ The reaction starts Na(s) ->Na+(aq) + e-(aq). Hydrated electrons are much more reactive than in liquid ammonia, but still catchable by their colour by 10000 fps fast cameras. It was also backup up by quantum chemistry simulation of behaviour of cluster of sodium atoms. Hydrated electrons than reduce water to H2 and OH-. $\endgroup$
    – Poutnik
    Oct 10, 2020 at 8:18
  • $\begingroup$ Thank you, @Poutnik. I believe I have correctly updated the equations to reflect this. $\endgroup$
    – neurosciencecalc
    Oct 13, 2020 at 5:38
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Sodium metal reacting with aqueous sodium hydroxide will continue to react, producing hydrogen ($\ce{H2}$) and sodium hydroxide ($\ce{NaOH}$). Eventually, however, the solution will become saturated with sodium hydroxide and the $\ce{NaOH}$ produced will form a coating on the outside of the sodium, preventing further reaction from occurring.

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    $\begingroup$ > Eventually, however, the solution will become saturated with sodium hydroxide and the NaOHNaOH produced will form a coating on the outside of the sodium, preventing further reaction from occurring. || sodium gladly reacts with sodium hydroxide at elevated temperature. Furthermore, 'saturated' aqueous solution for sodium hydroxide is 1:1 molar mixture. $\endgroup$
    – permeakra
    Aug 13, 2016 at 12:04
  • $\begingroup$ @permeakra I didn't know this before. What product will the reaction make, as a matter of interest? $\endgroup$
    – sadljkfhalskdjfh
    Aug 13, 2016 at 12:11
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    $\begingroup$ Sodium hydride and sodium oxide. $\endgroup$
    – permeakra
    Aug 13, 2016 at 12:27
  • $\begingroup$ what about room temperature, then it will follow what you said of coating or will there be a totally different reaction? $\endgroup$
    – user510
    Aug 13, 2016 at 15:22

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