So I was studying Chemistry (Hydrogen - Uses, Properties and Preparation) from 2 different textbooks (based on Grade 9 syllabus, I.C.S.E. Board, India) and I found what seems an astounding anomaly to me.

In the two textbooks, the same reaction for liberating Hydrogen gas from a hot concentrated solution of $\ce{NaOH}$ and $\ce{Al}$ is given as follows:-

Textbook 1: $\ce{2Al + 2NaOH + 2H2O -> \underset{\text{Sodium metaaluminate}}{2NaAlO2} + 3H2 ^}$

Textbook 2: $\ce{2Al + 2NaOH + 2H2O -> \underset{\text{Sodium aluminate}}{2NaAlO2} + 3H2 ^}$

If the two reactions are the same, why and how is the name of the same compound ($\ce{NaAlO2}$, Sodium meta aluminate / Sodium aluminate) different? Secondly, what does 'meta' imply in Sodium metaaluminate?

  • 2
    $\begingroup$ It is rather $\ce{[Al(OH)4]-}$, respectively $\ce{[Al(H2O)2(OH)4]-}$ $\endgroup$
    – Poutnik
    Commented Dec 30, 2022 at 18:42
  • 2
    $\begingroup$ There are multiple cases in chemistry when prefix is used either explicitly either implicitly. $\endgroup$
    – Poutnik
    Commented Dec 30, 2022 at 19:17
  • $\begingroup$ You may want to check: chemistry.stackexchange.com/questions/40506/… // Besides, if you look at the WP article of sodium aluminate, you can see sodium metaaluminate as one of the other names. $\endgroup$ Commented Dec 31, 2022 at 7:22

2 Answers 2


What appears to be an "astounding anomaly" to you is totally normal in chemical nomenclature and biological sciences in general. Remember is chemistry has been studied by millions of people for centuries. One cannot make them follow identical nomenclature rules, although general consesus is developed by IUPAC. Many chemical names have 10 or even more synonyms. If you study botany, a single plant may have plenty of radically different Latin names. Here are some more names (16) identified by SciFinder (Chemical Abstract Service, USA) for the same compound. I list only a few as examples. Now note that that some names may not the be standard ones.

In short, both texts are fine.

Aluminum sodium dioxide

Sodium aluminate ($\ce{Na2Al2O4}$)

Sodium aluminum dioxide

Sodium aluminum oxide ($\ce{NaAlO2}$)

Sodium metaaluminate ($\ce{NaAlO2}$)

  • 1
    $\begingroup$ Certainly yes, I seem to be too used to the standardization offered by Physics and many other sciences. But thank you very much for the answer! $\endgroup$ Commented Dec 31, 2022 at 7:09
  • $\begingroup$ Since physics heavily relies on mathematics, it is more consistent. However sign conventions in physics can also drive some students crazy! $\endgroup$
    – ACR
    Commented Dec 31, 2022 at 7:19

Seems like just a nomenclature thing to me. Prefixes meta, ortho and pyro are being sometimes used when giving names of inorganic acids to indicate a ratio of hydrogen atoms to the central atom(s).

And so:

  • meta means an acid with a minimal number of hydrogen atoms in relation to central atom (given its oxidation state), e.g. $\ce{(HPO3)n}$ is metaphosphoric(V) acid
  • ortho is a prefix given to an acid which has emperical formula having an H2O more than its meta acid counterpart, e.g. $\ce{H3PO4}$ is orthophosphoric(V) acid
  • pyro denotes an acid formed by condensation of an ortho acid, so pyrophosphoric(V) acid is $\ce{H4P2O7}$

In case of a compound from your question $\ce{NaAlO2}$ can be treated formally as a salt of "$\ce{HAlO2}$" acid - which would be of meta type. However, this a nomenclature thing so this prefix may be skipped.


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