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$\ce{HgCO3.3HgO}$ and $\ce{HgO.Hg(NH2)Cl}$ are called basic mercury carbonate and basic mercury amidochloride, respectively. I found this thread on the former; I've only seen the latter as the product of a qualitative test in one of my textbooks, and Google yields nothing on it.

Is "basic metal salt" a general term for salts of the form $\ce{M_yB_x.M_2O_x}$(M the metal, B some anion with valency y, x the valency of the metal) or is it just for some compounds of mercury? If it's just for mercury, which ones more are there?

Are there any "acidic salt" analogues? If so, what general formula do they have?

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There exist plenty of basic salts. For example,

  1. Copper produces a "simple" copper carbonate $\ce{CuCO3}$ as high $\ce{CO2}$ pressure. At lower pressures, the following basic copper carbonates are produced : $\ce{Cu3(CO3)2(OH)2}$ or $\ce{Cu2CO3(OH)2}$ (malachite), depending on the partial $\ce{CO2}$ pressure. Other copper salts produce basic copper salts like : $\ce{Cu2NO3(OH)3}$ , $\ce{Cu4(OH)6Cl2}$, $\ce{Cu4(OH)6SO4}$ .
  2. Zinc produces the two following basic zinc carbonates, according to the chosen pH : $\ce{Zn5(OH)6(CO3)2}$ or $\ce{Zn2CO3(OH)2}$
  3. Iron(III) produces also basic salts like $\ce{FeSO4(OH)}$ which is produced by air oxidation of iron(II) sulfate. Dilution of a ferric acetate solution produces a precipitate of basic acetate $\ce{Fe(CH3COO)(OH)2}$
  4. Aluminum solutions are often hydrolyzed producing basic salts. In the case of acetate, it gives a precipitate of basic acetate $\ce{Al(CH3COO)(OH)2}$
  5. Cobalt chloride solutions treated by cold NaOH solutions give a precipitate of basic chloride $\ce{CoClOH}$ When treated by carbonate solutions they produce a great variety of basic carbonates. This list is not exhaustive.
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  • $\begingroup$ Could you verify the criteria detailed in the comments above? That solves my problem. This answer is great, btw $\endgroup$
    – harry
    May 14, 2021 at 11:00
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    $\begingroup$ @Harry Holmes. Nilay Ghosh proposes three criteria, which can be discussed. 1) A basic salt must contain a hydroxide compound. No ! It may contain oxide ion $\ce{O^{2-}}$ like the mineral goethite $\ce{FeOOH}$. 2) Its overall pH is basic. It does not make any sense, as a precipitate or any solid does not have a pH value. 3) A basic salt is made using alcali compounds. NO ! It may be made using Barium hydroxide. And the example of impure potassium permanganate is poor. It is basic when insure may mean that it is not basic as a pure compound. $\endgroup$
    – Maurice
    May 14, 2021 at 11:12
  • $\begingroup$ I see. I could make a point for the second criterion, though; the basic pH might refer to the pH of the salt in solution. Either way, could you specify an alternate list of criteria? I know there aren't hard and fast rules for these common names, but a rough sketch would be helpful. $\endgroup$
    – harry
    May 14, 2021 at 11:16
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    $\begingroup$ @Harry Holmes. The pH of a solution made with an insoluble salt is a non-sense. It may happen that there is not even one atom of the insoluble salt per liter water. As to the possible rules about basic salts, I am afraid there are none. $\endgroup$
    – Maurice
    May 14, 2021 at 15:05

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