According to BBC Bitesize:

Carbonate ions, $\ce{CO_3^{2-}}$, are detected using a dilute acid. Bubbles are given off when an acid, usually dilute hydrochloric acid, is added to the test compound.

Is there a requirement that we use dilute acids for this purpose? Can't this test be done using relatively concentrated acids with the likely advantage that the reaction happens more vigorously?

  • 3
    $\begingroup$ Dilute HCl or HNO3 are quite acidic enough for the purpose. Safety first, which means you only take the potent reagents when they're really needed! And conc. acids might oxidise some other carbon-containing compound, which you then mistake for a carbonate. $\endgroup$
    – Karl
    Commented Jan 8, 2023 at 12:55
  • $\begingroup$ Nitric acid (dil) or (conc.) is never used for carbonate testing and the same applies to sulfuric acid. $\endgroup$
    – ACR
    Commented Jan 8, 2023 at 14:15
  • 1
    $\begingroup$ If you would post your comments as answers, I would gladly slap the checkmark on them. ;) $\endgroup$
    – Shane
    Commented Jan 8, 2023 at 15:28

1 Answer 1


BBC's story is quite an incomplete one. Many anions can form gaseous products when acidified. The reason for using a dilute acid for carbonate test is simply that it works and therefore one does not need a stronger concentration! Even lemon juice will work for carbonates. Since carbonate is a common anion, for elementary purposes, dilute HCl is the acid of choice because it does not form insoluble salts with commonly encountered carbonates such as alkali (Li, Na, K) and alkaline earth metals (Mg, Ca, Ba) etc. Sulfuric acid forms insoluble salt layer with Ca/Ba which can prevent further raction. Nitric acid (dilute or concentrated) is to avoided because it can also generate nitrogen oxide(s) bubbles in contact with certain substances depending on whatever is present along with carbonates.


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